[flags] warn about contradictory flags

Design Doc: https://docs.google.com/document/d/1lkvu8crkK7Ei39qjkPCFijpNyxWXsOktG9GB-7K34jM/

Bug: v8:10577
Change-Id: Ib9cfdffa401c48c895bf31caed5ee03545beddab
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2154792Reviewed-by: Clemens Backes <clemensb@chromium.org>
Reviewed-by: Michael Achenbach <machenbach@chromium.org>
Reviewed-by: Georg Neis <neis@chromium.org>
Reviewed-by: Tamer Tas <tmrts@chromium.org>
Commit-Queue: Tobias Tebbi <tebbi@chromium.org>
Cr-Commit-Position: refs/heads/master@{#68168}

src/d8/d8.cc

@@ -3172,6 +3172,7 @@ bool Shell::SetOptions(int argc, char* argv[]) {
     }
   }
 
+  i::FLAG_abort_on_contradictory_flags = true;
   v8::V8::SetFlagsFromCommandLine(&argc, argv, true);
   options.mock_arraybuffer_allocator = i::FLAG_mock_arraybuffer_allocator;
   options.mock_arraybuffer_allocator_limit =
@@ -3618,12 +3619,11 @@ class D8Testing {
         "--max-inlined-bytecode-size=999999 "
         "--max-inlined-bytecode-size-cumulative=999999 "
         "--noalways-opt";
-    static const char* kForcedOptimizations = "--always-opt";
 
-    if (run == GetStressRuns() - 1) {
-      V8::SetFlagsFromString(kForcedOptimizations);
-    } else {
+    if (run < GetStressRuns() - 1) {
       V8::SetFlagsFromString(kLazyOptimizations);
+    } else {
+      i::FLAG_always_opt = true;
     }
   }
 

src/flags/flag-definitions.h

@@ -15,6 +15,11 @@
 #define DEFINE_IMPLICATION(whenflag, thenflag) \
   DEFINE_VALUE_IMPLICATION(whenflag, thenflag, true)
 
+// A weak implication will be overwritten by a normal implication or by an
+// explicit flag.
+#define DEFINE_WEAK_IMPLICATION(whenflag, thenflag) \
+  DEFINE_WEAK_VALUE_IMPLICATION(whenflag, thenflag, true)
+
 #define DEFINE_NEG_IMPLICATION(whenflag, thenflag) \
   DEFINE_VALUE_IMPLICATION(whenflag, thenflag, false)
 
@@ -59,14 +64,22 @@
 
 // We produce the code to set flags when it is implied by another flag.
 #elif defined(FLAG_MODE_DEFINE_IMPLICATIONS)
-#define DEFINE_VALUE_IMPLICATION(whenflag, thenflag, value) \
-  if (FLAG_##whenflag) FLAG_##thenflag = value;
+#define DEFINE_VALUE_IMPLICATION(whenflag, thenflag, value)                   \
+  changed |= TriggerImplication(FLAG_##whenflag, #whenflag, &FLAG_##thenflag, \
+                                value, false);
+
+// A weak implication will be overwritten by a normal implication or by an
+// explicit flag.
+#define DEFINE_WEAK_VALUE_IMPLICATION(whenflag, thenflag, value)              \
+  changed |= TriggerImplication(FLAG_##whenflag, #whenflag, &FLAG_##thenflag, \
+                                value, true);
 
 #define DEFINE_GENERIC_IMPLICATION(whenflag, statement) \
   if (FLAG_##whenflag) statement;
 
-#define DEFINE_NEG_VALUE_IMPLICATION(whenflag, thenflag, value) \
-  if (!FLAG_##whenflag) FLAG_##thenflag = value;
+#define DEFINE_NEG_VALUE_IMPLICATION(whenflag, thenflag, value)                \
+  changed |= TriggerImplication(!FLAG_##whenflag, #whenflag, &FLAG_##thenflag, \
+                                value, false);
 
 // We apply a generic macro to the flags.
 #elif defined(FLAG_MODE_APPLY)
@@ -94,6 +107,10 @@
 #define DEFINE_VALUE_IMPLICATION(whenflag, thenflag, value)
 #endif
 
+#ifndef DEFINE_WEAK_VALUE_IMPLICATION
+#define DEFINE_WEAK_VALUE_IMPLICATION(whenflag, thenflag, value)
+#endif
+
 #ifndef DEFINE_GENERIC_IMPLICATION
 #define DEFINE_GENERIC_IMPLICATION(whenflag, statement)
 #endif
@@ -203,6 +220,14 @@ struct MaybeBoolFlag {
 //
 #define FLAG FLAG_FULL
 
+// ATTENTION: This is set to true by default in d8. But For API compatibility,
+// it generally defaults to false.
+DEFINE_BOOL(abort_on_contradictory_flags, false,
+            "Disallow flags or implications overriding each other.")
+// This implication is also hard-coded into the flags processing to make sure it
+// becomes active before we even process subsequent flags.
+DEFINE_NEG_IMPLICATION(fuzzing, abort_on_contradictory_flags)
+
 // Flags for language modes and experimental language features.
 DEFINE_BOOL(use_strict, false, "enforce strict mode")
 
@@ -373,8 +398,23 @@ DEFINE_BOOL(future, FUTURE_BOOL,
             "Implies all staged features that we want to ship in the "
             "not-too-far future")
 
-DEFINE_IMPLICATION(future, write_protect_code_memory)
-DEFINE_IMPLICATION(future, finalize_streaming_on_background)
+DEFINE_WEAK_IMPLICATION(future, write_protect_code_memory)
+DEFINE_WEAK_IMPLICATION(future, finalize_streaming_on_background)
+
+// Flags for jitless
+DEFINE_BOOL(jitless, V8_LITE_BOOL,
+            "Disable runtime allocation of executable memory.")
+
+// Jitless V8 has a few implications:
+DEFINE_NEG_IMPLICATION(jitless, opt)
+// Field representation tracking is only used by TurboFan.
+DEFINE_NEG_IMPLICATION(jitless, track_field_types)
+DEFINE_NEG_IMPLICATION(jitless, track_heap_object_fields)
+// Regexps are interpreted.
+DEFINE_IMPLICATION(jitless, regexp_interpret_all)
+// asm.js validation is disabled since it triggers wasm code generation.
+DEFINE_NEG_IMPLICATION(jitless, validate_asm)
+// --jitless also implies --no-expose-wasm, see InitializeOncePerProcessImpl.
 
 DEFINE_BOOL(assert_types, false,
             "generate runtime type assertions to test the typer")
@@ -427,21 +467,6 @@ DEFINE_BOOL_READONLY(string_slices, true, "use string slices")
 DEFINE_INT(interrupt_budget, 144 * KB,
            "interrupt budget which should be used for the profiler counter")
 
-// Flags for jitless
-DEFINE_BOOL(jitless, V8_LITE_BOOL,
-            "Disable runtime allocation of executable memory.")
-
-// Jitless V8 has a few implications:
-DEFINE_NEG_IMPLICATION(jitless, opt)
-// Field representation tracking is only used by TurboFan.
-DEFINE_NEG_IMPLICATION(jitless, track_field_types)
-DEFINE_NEG_IMPLICATION(jitless, track_heap_object_fields)
-// Regexps are interpreted.
-DEFINE_IMPLICATION(jitless, regexp_interpret_all)
-// asm.js validation is disabled since it triggers wasm code generation.
-DEFINE_NEG_IMPLICATION(jitless, validate_asm)
-// --jitless also implies --no-expose-wasm, see InitializeOncePerProcessImpl.
-
 // Flags for inline caching and feedback vectors.
 DEFINE_BOOL(use_ic, true, "use inline caching")
 DEFINE_INT(budget_for_feedback_vector_allocation, 1 * KB,
@@ -514,7 +539,7 @@ DEFINE_BOOL(concurrent_inlining, false,
             "run optimizing compiler's inlining phase on a separate thread")
 DEFINE_INT(max_serializer_nesting, 25,
            "maximum levels for nesting child serializers")
-DEFINE_IMPLICATION(future, concurrent_inlining)
+DEFINE_WEAK_IMPLICATION(future, concurrent_inlining)
 DEFINE_BOOL(trace_heap_broker_verbose, false,
             "trace the heap broker verbosely (all reports)")
 DEFINE_BOOL(trace_heap_broker_memory, false,
@@ -726,7 +751,7 @@ DEFINE_BOOL(liftoff, true,
 #else
 DEFINE_BOOL(liftoff, false,
             "enable Liftoff, the baseline compiler for WebAssembly")
-DEFINE_IMPLICATION(future, liftoff)
+DEFINE_WEAK_IMPLICATION(future, liftoff)
 #endif
 // We can't tier up (from Liftoff to TurboFan) in single-threaded mode, hence
 // disable Liftoff in that configuration for now. The alternative is disabling
@@ -1813,9 +1838,11 @@ DEFINE_IMPLICATION(unbox_double_fields, track_double_fields)
 #undef DEFINE_STRING
 #undef DEFINE_FLOAT
 #undef DEFINE_IMPLICATION
+#undef DEFINE_WEAK_IMPLICATION
 #undef DEFINE_NEG_IMPLICATION
 #undef DEFINE_NEG_VALUE_IMPLICATION
 #undef DEFINE_VALUE_IMPLICATION
+#undef DEFINE_WEAK_VALUE_IMPLICATION
 #undef DEFINE_GENERIC_IMPLICATION
 #undef DEFINE_ALIAS_BOOL
 #undef DEFINE_ALIAS_INT

src/flags/flags.cc

@@ -8,9 +8,11 @@
 #include <cerrno>
 #include <cinttypes>
 #include <cstdlib>
+#include <cstring>
 #include <sstream>
 
 #include "src/base/functional.h"
+#include "src/base/logging.h"
 #include "src/base/platform/platform.h"
 #include "src/codegen/cpu-features.h"
 #include "src/logging/counters.h"
@@ -33,6 +35,10 @@ namespace internal {
 
 namespace {
 
+struct Flag;
+Flag* FindFlagByPointer(const void* ptr);
+Flag* FindFlagByName(const char* name);
+
 // This structure represents a single entry in the flag system, with a pointer
 // to the actual flag, default value, comment, etc.  This is designed to be POD
 // initialized as to avoid requiring static constructors.
@@ -48,12 +54,16 @@ struct Flag {
     TYPE_STRING,
   };
 
+  enum class SetBy { kDefault, kWeakImplication, kImplication, kCommandLine };
+
   FlagType type_;       // What type of flag, bool, int, or string.
   const char* name_;    // Name of the flag, ex "my_flag".
   void* valptr_;        // Pointer to the global flag variable.
   const void* defptr_;  // Pointer to the default value.
   const char* cmt_;     // A comment about the flags purpose.
   bool owns_ptr_;       // Does the flag own its string value?
+  SetBy set_by_ = SetBy::kDefault;
+  const char* implied_by_ = nullptr;
 
   FlagType type() const { return type_; }
 
@@ -61,39 +71,90 @@ struct Flag {
 
   const char* comment() const { return cmt_; }
 
-  bool* bool_variable() const {
+  bool PointsTo(const void* ptr) const { return valptr_ == ptr; }
+
+  bool bool_variable() const {
+    DCHECK(type_ == TYPE_BOOL);
+    return *reinterpret_cast<bool*>(valptr_);
+  }
+
+  void set_bool_variable(bool value, SetBy set_by) {
     DCHECK(type_ == TYPE_BOOL);
-    return reinterpret_cast<bool*>(valptr_);
+    bool change_flag = *reinterpret_cast<bool*>(valptr_) != value;
+    change_flag = CheckFlagChange(set_by, change_flag);
+    if (change_flag) *reinterpret_cast<bool*>(valptr_) = value;
   }
 
-  MaybeBoolFlag* maybe_bool_variable() const {
+  MaybeBoolFlag maybe_bool_variable() const {
     DCHECK(type_ == TYPE_MAYBE_BOOL);
-    return reinterpret_cast<MaybeBoolFlag*>(valptr_);
+    return *reinterpret_cast<MaybeBoolFlag*>(valptr_);
+  }
+
+  void set_maybe_bool_variable(MaybeBoolFlag value, SetBy set_by) {
+    DCHECK(type_ == TYPE_MAYBE_BOOL);
+    bool change_flag = *reinterpret_cast<MaybeBoolFlag*>(valptr_) != value;
+    change_flag = CheckFlagChange(set_by, change_flag);
+    if (change_flag) *reinterpret_cast<MaybeBoolFlag*>(valptr_) = value;
+  }
+
+  int int_variable() const {
+    DCHECK(type_ == TYPE_INT);
+    return *reinterpret_cast<int*>(valptr_);
   }
 
-  int* int_variable() const {
+  void set_int_variable(int value, SetBy set_by) {
     DCHECK(type_ == TYPE_INT);
-    return reinterpret_cast<int*>(valptr_);
+    bool change_flag = *reinterpret_cast<int*>(valptr_) != value;
+    change_flag = CheckFlagChange(set_by, change_flag);
+    if (change_flag) *reinterpret_cast<int*>(valptr_) = value;
   }
 
-  unsigned int* uint_variable() const {
+  unsigned int uint_variable() const {
     DCHECK(type_ == TYPE_UINT);
-    return reinterpret_cast<unsigned int*>(valptr_);
+    return *reinterpret_cast<unsigned int*>(valptr_);
   }
 
-  uint64_t* uint64_variable() const {
+  void set_uint_variable(unsigned int value, SetBy set_by) {
+    DCHECK(type_ == TYPE_UINT);
+    bool change_flag = *reinterpret_cast<unsigned int*>(valptr_) != value;
+    change_flag = CheckFlagChange(set_by, change_flag);
+    if (change_flag) *reinterpret_cast<unsigned int*>(valptr_) = value;
+  }
+
+  uint64_t uint64_variable() const {
+    DCHECK(type_ == TYPE_UINT64);
+    return *reinterpret_cast<uint64_t*>(valptr_);
+  }
+
+  void set_uint64_variable(uint64_t value, SetBy set_by) {
     DCHECK(type_ == TYPE_UINT64);
-    return reinterpret_cast<uint64_t*>(valptr_);
+    bool change_flag = *reinterpret_cast<uint64_t*>(valptr_) != value;
+    change_flag = CheckFlagChange(set_by, change_flag);
+    if (change_flag) *reinterpret_cast<uint64_t*>(valptr_) = value;
   }
 
-  double* float_variable() const {
+  double float_variable() const {
     DCHECK(type_ == TYPE_FLOAT);
-    return reinterpret_cast<double*>(valptr_);
+    return *reinterpret_cast<double*>(valptr_);
+  }
+
+  void set_float_variable(double value, SetBy set_by) {
+    DCHECK(type_ == TYPE_FLOAT);
+    bool change_flag = *reinterpret_cast<double*>(valptr_) != value;
+    change_flag = CheckFlagChange(set_by, change_flag);
+    if (change_flag) *reinterpret_cast<double*>(valptr_) = value;
+  }
+
+  size_t size_t_variable() const {
+    DCHECK(type_ == TYPE_SIZE_T);
+    return *reinterpret_cast<size_t*>(valptr_);
   }
 
-  size_t* size_t_variable() const {
+  void set_size_t_variable(size_t value, SetBy set_by) {
     DCHECK(type_ == TYPE_SIZE_T);
-    return reinterpret_cast<size_t*>(valptr_);
+    bool change_flag = *reinterpret_cast<size_t*>(valptr_) != value;
+    change_flag = CheckFlagChange(set_by, change_flag);
+    if (change_flag) *reinterpret_cast<size_t*>(valptr_) = value;
   }
 
   const char* string_value() const {
@@ -101,12 +162,19 @@ struct Flag {
     return *reinterpret_cast<const char**>(valptr_);
   }
 
-  void set_string_value(const char* value, bool owns_ptr) {
+  void set_string_value(const char* value, bool owns_ptr, SetBy set_by) {
     DCHECK(type_ == TYPE_STRING);
     const char** ptr = reinterpret_cast<const char**>(valptr_);
-    if (owns_ptr_ && *ptr != nullptr) DeleteArray(*ptr);
-    *ptr = value;
-    owns_ptr_ = owns_ptr;
+    bool change_flag = (*ptr == nullptr) != (value == nullptr) ||
+                       (*ptr && value && std::strcmp(*ptr, value) != 0);
+    change_flag = CheckFlagChange(set_by, change_flag);
+    if (change_flag) {
+      if (owns_ptr_ && *ptr != nullptr) DeleteArray(*ptr);
+      *ptr = value;
+      owns_ptr_ = owns_ptr;
+    } else {
+      if (owns_ptr && value != nullptr) DeleteArray(value);
+    }
   }
 
   bool bool_default() const {
@@ -144,23 +212,83 @@ struct Flag {
     return *reinterpret_cast<const char* const*>(defptr_);
   }
 
+  static bool ShouldCheckFlagContradictions() {
+    return FLAG_abort_on_contradictory_flags && !FLAG_fuzzing;
+  }
+
+  // {change_flag} indicates if we're going to change the flag value.
+  // Returns an updated value for {change_flag}, which is changed to false if a
+  // weak implication is being ignored beause a flag is already set by a normal
+  // implication or from the command line.
+  bool CheckFlagChange(SetBy new_set_by, bool change_flag,
+                       const char* implied_by = nullptr) {
+    if (new_set_by == SetBy::kWeakImplication &&
+        (set_by_ == SetBy::kImplication || set_by_ == SetBy::kCommandLine)) {
+      return false;
+    }
+    if (ShouldCheckFlagContradictions() && change_flag) {
+      const char* hint =
+          "INCOMPATIBLE_FLAGS_PER_VARIANT in "
+          "tools/testrunner/local/variants.py might be missing a flag for the "
+          "current variant.";
+      switch (set_by_) {
+        case SetBy::kDefault:
+          break;
+        case SetBy::kWeakImplication:
+          if (new_set_by == SetBy::kWeakImplication) {
+            FATAL(
+                "Contradictory weak flag implications from --%s and --%s for "
+                "flag %s\n%s",
+                implied_by_, implied_by, name(), hint);
+          }
+          break;
+        case SetBy::kImplication:
+          if (new_set_by == SetBy::kImplication) {
+            FATAL(
+                "Contradictory flag implications from --%s and --%s for flag "
+                "%s\n%s",
+                implied_by_, implied_by, name(), hint);
+          }
+          break;
+        case SetBy::kCommandLine:
+          if (new_set_by == SetBy::kImplication) {
+            FATAL(
+                "Flag implication from --%s contradicts explicitly provided "
+                "argument for flag --%s\n%s",
+                implied_by, name(), hint);
+          } else if (new_set_by == SetBy::kCommandLine) {
+            FATAL("Contradictory user-provided values for flag --%s\n%s",
+                  name(), hint);
+          }
+          break;
+      }
+    }
+    set_by_ = new_set_by;
+    if (new_set_by == SetBy::kImplication ||
+        new_set_by == SetBy::kWeakImplication) {
+      DCHECK_NOT_NULL(implied_by);
+      implied_by_ = implied_by;
+    }
+    return change_flag;
+  }
+
   // Compare this flag's current value against the default.
   bool IsDefault() const {
     switch (type_) {
       case TYPE_BOOL:
-        return *bool_variable() == bool_default();
+        return bool_variable() == bool_default();
       case TYPE_MAYBE_BOOL:
-        return maybe_bool_variable()->has_value == false;
+        return maybe_bool_variable().has_value == false;
       case TYPE_INT:
-        return *int_variable() == int_default();
+        return int_variable() == int_default();
       case TYPE_UINT:
-        return *uint_variable() == uint_default();
+        return uint_variable() == uint_default();
       case TYPE_UINT64:
-        return *uint64_variable() == uint64_default();
+        return uint64_variable() == uint64_default();
       case TYPE_FLOAT:
-        return *float_variable() == float_default();
+        return float_variable() == float_default();
       case TYPE_SIZE_T:
-        return *size_t_variable() == size_t_default();
+        return size_t_variable() == size_t_default();
       case TYPE_STRING: {
         const char* str1 = string_value();
         const char* str2 = string_default();
@@ -176,31 +304,34 @@ struct Flag {
   void Reset() {
     switch (type_) {
       case TYPE_BOOL:
-        *bool_variable() = bool_default();
+        set_bool_variable(bool_default(), SetBy::kDefault);
         break;
       case TYPE_MAYBE_BOOL:
-        *maybe_bool_variable() = MaybeBoolFlag::Create(false, false);
+        set_maybe_bool_variable(MaybeBoolFlag::Create(false, false),
+                                SetBy::kDefault);
         break;
       case TYPE_INT:
-        *int_variable() = int_default();
+        set_int_variable(int_default(), SetBy::kDefault);
         break;
       case TYPE_UINT:
-        *uint_variable() = uint_default();
+        set_uint_variable(uint_default(), SetBy::kDefault);
         break;
       case TYPE_UINT64:
-        *uint64_variable() = uint64_default();
+        set_uint64_variable(uint64_default(), SetBy::kDefault);
         break;
       case TYPE_FLOAT:
-        *float_variable() = float_default();
+        set_float_variable(float_default(), SetBy::kDefault);
         break;
       case TYPE_SIZE_T:
-        *size_t_variable() = size_t_default();
+        set_size_t_variable(size_t_default(), SetBy::kDefault);
         break;
       case TYPE_STRING:
-        set_string_value(string_default(), false);
+        set_string_value(string_default(), false, SetBy::kDefault);
         break;
     }
   }
+
+  void AllowOverwriting() { set_by_ = SetBy::kDefault; }
 };
 
 Flag flags[] = {
@@ -210,6 +341,31 @@ Flag flags[] = {
 
 const size_t num_flags = sizeof(flags) / sizeof(*flags);
 
+inline char NormalizeChar(char ch) { return ch == '_' ? '-' : ch; }
+
+bool EqualNames(const char* a, const char* b) {
+  for (int i = 0; NormalizeChar(a[i]) == NormalizeChar(b[i]); i++) {
+    if (a[i] == '\0') {
+      return true;
+    }
+  }
+  return false;
+}
+
+Flag* FindFlagByName(const char* name) {
+  for (size_t i = 0; i < num_flags; ++i) {
+    if (EqualNames(name, flags[i].name())) return &flags[i];
+  }
+  return nullptr;
+}
+
+Flag* FindFlagByPointer(const void* ptr) {
+  for (size_t i = 0; i < num_flags; ++i) {
+    if (flags[i].PointsTo(ptr)) return &flags[i];
+  }
+  return nullptr;
+}
+
 }  // namespace
 
 static const char* Type2String(Flag::FlagType type) {
@@ -237,27 +393,27 @@ static const char* Type2String(Flag::FlagType type) {
 std::ostream& operator<<(std::ostream& os, const Flag& flag) {  // NOLINT
   switch (flag.type()) {
     case Flag::TYPE_BOOL:
-      os << (*flag.bool_variable() ? "true" : "false");
+      os << (flag.bool_variable() ? "true" : "false");
       break;
     case Flag::TYPE_MAYBE_BOOL:
-      os << (flag.maybe_bool_variable()->has_value
-                 ? (flag.maybe_bool_variable()->value ? "true" : "false")
+      os << (flag.maybe_bool_variable().has_value
+                 ? (flag.maybe_bool_variable().value ? "true" : "false")
                  : "unset");
       break;
     case Flag::TYPE_INT:
-      os << *flag.int_variable();
+      os << flag.int_variable();
       break;
     case Flag::TYPE_UINT:
-      os << *flag.uint_variable();
+      os << flag.uint_variable();
       break;
     case Flag::TYPE_UINT64:
-      os << *flag.uint64_variable();
+      os << flag.uint64_variable();
       break;
     case Flag::TYPE_FLOAT:
-      os << *flag.float_variable();
+      os << flag.float_variable();
       break;
     case Flag::TYPE_SIZE_T:
-      os << *flag.size_t_variable();
+      os << flag.size_t_variable();
       break;
     case Flag::TYPE_STRING: {
       const char* str = flag.string_value();
@@ -275,7 +431,7 @@ std::vector<const char*>* FlagList::argv() {
     Flag* f = &flags[i];
     if (!f->IsDefault()) {
       {
-        bool disabled = f->type() == Flag::TYPE_BOOL && !*f->bool_variable();
+        bool disabled = f->type() == Flag::TYPE_BOOL && !f->bool_variable();
         std::ostringstream os;
         os << (disabled ? "--no" : "--") << f->name();
         args->push_back(StrDup(os.str().c_str()));
@@ -290,8 +446,6 @@ std::vector<const char*>* FlagList::argv() {
   return args;
 }
 
-inline char NormalizeChar(char ch) { return ch == '_' ? '-' : ch; }
-
 // Helper function to parse flags: Takes an argument arg and splits it into
 // a flag name and flag value (or nullptr if they are missing). negated is set
 // if the arg started with "-no" or "--no". The buffer may be used to NUL-
@@ -334,22 +488,6 @@ static void SplitArgument(const char* arg, char* buffer, int buffer_size,
   }
 }
 
-static bool EqualNames(const char* a, const char* b) {
-  for (int i = 0; NormalizeChar(a[i]) == NormalizeChar(b[i]); i++) {
-    if (a[i] == '\0') {
-      return true;
-    }
-  }
-  return false;
-}
-
-static Flag* FindFlag(const char* name) {
-  for (size_t i = 0; i < num_flags; ++i) {
-    if (EqualNames(name, flags[i].name())) return &flags[i];
-  }
-  return nullptr;
-}
-
 template <typename T>
 bool TryParseUnsigned(Flag* flag, const char* arg, const char* value,
                       char** endp, T* out_val) {
@@ -388,7 +526,7 @@ int FlagList::SetFlagsFromCommandLine(int* argc, char** argv,
 
     if (name != nullptr) {
       // lookup the flag
-      Flag* flag = FindFlag(name);
+      Flag* flag = FindFlagByName(name);
       if (flag == nullptr) {
         if (remove_flags) {
           // We don't recognize this flag but since we're removing
@@ -421,37 +559,50 @@ int FlagList::SetFlagsFromCommandLine(int* argc, char** argv,
       char* endp = const_cast<char*>("");  // *endp is only read
       switch (flag->type()) {
         case Flag::TYPE_BOOL:
-          *flag->bool_variable() = !negated;
+          flag->set_bool_variable(!negated, Flag::SetBy::kCommandLine);
           break;
         case Flag::TYPE_MAYBE_BOOL:
-          *flag->maybe_bool_variable() = MaybeBoolFlag::Create(true, !negated);
+          flag->set_maybe_bool_variable(MaybeBoolFlag::Create(true, !negated),
+                                        Flag::SetBy::kCommandLine);
           break;
         case Flag::TYPE_INT:
-          *flag->int_variable() = static_cast<int>(strtol(value, &endp, 10));
+          flag->set_int_variable(static_cast<int>(strtol(value, &endp, 10)),
+                                 Flag::SetBy::kCommandLine);
           break;
-        case Flag::TYPE_UINT:
-          if (!TryParseUnsigned(flag, arg, value, &endp,
-                                flag->uint_variable())) {
+        case Flag::TYPE_UINT: {
+          unsigned int parsed_value;
+          if (TryParseUnsigned(flag, arg, value, &endp, &parsed_value)) {
+            flag->set_uint_variable(parsed_value, Flag::SetBy::kCommandLine);
+          } else {
             return_code = j;
           }
           break;
-        case Flag::TYPE_UINT64:
-          if (!TryParseUnsigned(flag, arg, value, &endp,
-                                flag->uint64_variable())) {
+        }
+        case Flag::TYPE_UINT64: {
+          uint64_t parsed_value;
+          if (TryParseUnsigned(flag, arg, value, &endp, &parsed_value)) {
+            flag->set_uint64_variable(parsed_value, Flag::SetBy::kCommandLine);
+          } else {
             return_code = j;
           }
           break;
+        }
         case Flag::TYPE_FLOAT:
-          *flag->float_variable() = strtod(value, &endp);
+          flag->set_float_variable(strtod(value, &endp),
+                                   Flag::SetBy::kCommandLine);
           break;
-        case Flag::TYPE_SIZE_T:
-          if (!TryParseUnsigned(flag, arg, value, &endp,
-                                flag->size_t_variable())) {
+        case Flag::TYPE_SIZE_T: {
+          size_t parsed_value;
+          if (TryParseUnsigned(flag, arg, value, &endp, &parsed_value)) {
+            flag->set_size_t_variable(parsed_value, Flag::SetBy::kCommandLine);
+          } else {
             return_code = j;
           }
           break;
+        }
         case Flag::TYPE_STRING:
-          flag->set_string_value(value ? StrDup(value) : nullptr, true);
+          flag->set_string_value(value ? StrDup(value) : nullptr, true,
+                                 Flag::SetBy::kCommandLine);
           break;
       }
 
@@ -590,6 +741,8 @@ void FlagList::PrintHelp() {
   }
 }
 
+namespace {
+
 static uint32_t flag_hash = 0;
 
 void ComputeFlagListHash() {
@@ -602,8 +755,7 @@ void ComputeFlagListHash() {
   }
   for (size_t i = 0; i < num_flags; ++i) {
     Flag* current = &flags[i];
-    if (current->type() == Flag::TYPE_BOOL &&
-        current->bool_variable() == &FLAG_profile_deserialization) {
+    if (current->PointsTo(&FLAG_profile_deserialization)) {
       // We want to be able to flip --profile-deserialization without
       // causing the code cache to get invalidated by this hash.
       continue;
@@ -618,11 +770,39 @@ void ComputeFlagListHash() {
       base::hash_range(args.c_str(), args.c_str() + args.length()));
 }
 
+template <class T>
+struct Identity {
+  using type = T;
+};
+
+template <class A>
+bool TriggerImplication(bool premise, const char* premise_name,
+                        A* conclusion_pointer, typename Identity<A>::type value,
+                        bool weak_implication) {
+  if (premise) {
+    bool change_flag = *conclusion_pointer != value;
+    Flag* conclusion_flag = FindFlagByPointer(conclusion_pointer);
+    change_flag = conclusion_flag->CheckFlagChange(
+        weak_implication ? Flag::SetBy::kWeakImplication
+                         : Flag::SetBy::kImplication,
+        change_flag, premise_name);
+    if (change_flag) *conclusion_pointer = value;
+    return change_flag;
+  }
+  return false;
+}
+
+}  // namespace
+
 // static
 void FlagList::EnforceFlagImplications() {
+  bool changed;
+  do {
+    changed = false;
 #define FLAG_MODE_DEFINE_IMPLICATIONS
 #include "src/flags/flag-definitions.h"  // NOLINT(build/include)
 #undef FLAG_MODE_DEFINE_IMPLICATIONS
+  } while (changed);
   ComputeFlagListHash();
 }
 

test/inspector/inspector-test.cc

@@ -1056,6 +1056,7 @@ int main(int argc, char* argv[]) {
   v8::V8::InitializeICUDefaultLocation(argv[0]);
   std::unique_ptr<v8::Platform> platform(v8::platform::NewDefaultPlatform());
   v8::V8::InitializePlatform(platform.get());
+  v8::internal::FLAG_abort_on_contradictory_flags = true;
   v8::V8::SetFlagsFromCommandLine(&argc, argv, true);
   v8::V8::InitializeExternalStartupData(argv[0]);
   v8::V8::Initialize();

test/message/wasm-trace-memory-liftoff.js

@@ -2,7 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-// Flags: --no-stress-opt --trace-wasm-memory --liftoff --no-future
+// Flags: --no-stress-opt --trace-wasm-memory --liftoff
 // Flags: --no-wasm-tier-up --experimental-wasm-simd
 // Flags: --enable-sse3 --enable-sse4-1
 

test/message/wasm-trace-memory.js

@@ -2,7 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-// Flags: --no-stress-opt --trace-wasm-memory --no-liftoff --no-future
+// Flags: --no-stress-opt --trace-wasm-memory --no-liftoff
 // Flags: --experimental-wasm-simd
 
 load("test/mjsunit/wasm/wasm-module-builder.js");

test/mjsunit/ensure-growing-store-learns.js

@@ -2,8 +2,15 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-// Flags: --allow-natives-syntax --noverify-heap --noenable-slow-asserts
-// Flags: --opt --no-always-opt
+// The flags are processed left to right. --no-abort-on-contradictory-flags
+// disables the checking for conflicts, then we process --noverify-heap and
+// --noenable-slow-asserts, which the test runner already set to true before.
+// This causes the flags to be overwritten while silencing the error. Then we
+// re-enable --abort-on-contradictory-flags to make sure that the processing of
+// other flags and flag implications, which happens later, still produces
+// errors.
+// Flags: --no-abort-on-contradictory-flags --noverify-heap --noenable-slow-asserts --abort-on-contradictory-flags
+// Flags: --allow-natives-syntax --opt --no-always-opt
 
 // --noverify-heap and --noenable-slow-asserts are set because the test is too
 // slow with it on.

test/mjsunit/mjsunit.status

@@ -367,17 +367,6 @@
   'regexp-tier-up-multiple': [SKIP],
   'regress/regress-996234': [SKIP],
 
-  # Tests that depend on optimization (beyond doing assertOptimized).
-  'compiler/is-being-interpreted-*': [SKIP],
-  'compiler/serializer-accessors': [SKIP],
-  'compiler/serializer-apply': [SKIP],
-  'compiler/serializer-call': [SKIP],
-  'compiler/serializer-dead-after-jump': [SKIP],
-  'compiler/serializer-dead-after-return': [SKIP],
-  'compiler/serializer-transition-propagation': [SKIP],
-  'regress/regress-1049982-1': [SKIP],
-  'regress/regress-1049982-2': [SKIP],
-
   # These tests check that we can trace the compiler.
   'tools/compiler-trace-flags': [SKIP],
   'tools/compiler-trace-flags-wasm': [SKIP],
@@ -1153,10 +1142,6 @@
   'regress/regress-1049982-2': [SKIP],
   'es6/iterator-eager-deopt': [SKIP],
 
-  # interrupt_budget overrides don't work with TurboProp.
-  'interrupt-budget-override': [SKIP],
-  'never-optimize': [SKIP],
-
   # In turboprop we reuse the optimized code on soft deopt. The following tests
   # test for a soft deopt and they won't work in TurboProp.
   'deopt-recursive-soft-once': [SKIP],

test/mjsunit/random-bit-correlations.js

@@ -2,7 +2,15 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-// Flags: --random-seed=20 --nostress-opt --noalways-opt --predictable
+// Overwrite the random seed provided by the test runner to make this test less
+// flaky.
+// The flags are processed left to right. --no-abort-on-contradictory-flags
+// disables the checking for conflicts, then we process --random-seed=20 to
+// overwrite the value the test runner already set before. Then we re-enable
+// --abort-on-contradictory-flags to make sure that the processing of other
+// flags and flag implications, which happens later, still produces errors.
+// Flags: --no-abort-on-contradictory-flags --random-seed=20 --abort-on-contradictory-flags
+// Flags: --nostress-opt --noalways-opt --predictable
 
 (function() {
   var kHistory = 2;

test/mjsunit/regress/regress-356053.js

@@ -2,7 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-// Flags: --noconcurrent-recompilation --expose-gc --allow-natives-syntax
+// Flags: --expose-gc --allow-natives-syntax
 // Flags: --concurrent-recompilation --block-concurrent-recompilation
 
 gc();

test/mjsunit/regress/regress-411210.js

@@ -2,7 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-// Flags: --allow-natives-syntax --gc-interval=439 --random-seed=-423594851
+// Flags: --allow-natives-syntax --gc-interval=439
 
 var __v_3;
 function __f_2() {

test/mjsunit/regress/regress-487981.js

@@ -4,7 +4,7 @@
 
 // Flags:  --allow-natives-syntax --stress-compaction
 
-// To reliably reproduce the crash use --verify-heap --random-seed=-133185440
+// To reliably reproduce the crash use --verify-heap
 
 function __f_2(o) {
   return o.field.b.x;

test/mjsunit/regress/regress-8265.js

@@ -2,8 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-// Flags: --random-seed=1
-
 for (let i = 0; i < 54; ++i) Math.random();
 let sum = 0;
 for (let i = 0; i < 10; ++i)

test/mjsunit/regress/regress-863810.js

@@ -2,7 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-// Flags: --no-liftoff --no-future --debug-code
+// Flags: --no-liftoff --debug-code
 
 load('test/mjsunit/wasm/wasm-module-builder.js');
 

test/mjsunit/regress/regress-883059.js

@@ -2,6 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-// Flags: --random-seed=-1595876594 --disable-in-process-stack-traces  --no-lazy
+// Flags: --disable-in-process-stack-traces  --no-lazy
 
 var __v_47 = ({[__v_46]: __f_52}) => { var __v_46 = 'b'; return __f_52; };

test/mjsunit/regress/regress-crbug-664506.js

@@ -2,7 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-// Flags: --expose-gc --predictable --random-seed=-1109634722
+// Flags: --expose-gc --predictable
 
 gc();
 gc();

test/mjsunit/regress/wasm/regress-02256.js

@@ -2,7 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 //
-// Flags: --random-seed=891196975 --expose-gc --allow-natives-syntax
+// Flags: --expose-gc --allow-natives-syntax
 // Flags: --gc-interval=207 --stress-compaction --validate-asm
 // Flags: --opt --no-always-opt
 //

test/mjsunit/regress/wasm/regress-02256b.js

@@ -2,9 +2,8 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 //
-// Flags: --random-seed=891196975 --expose-gc --allow-natives-syntax
-// Flags: --gc-interval=207 --stress-compaction --validate-asm
-// Flags: --opt --no-always-opt
+// Flags: --expose-gc --allow-natives-syntax --gc-interval=207
+// Flags: --stress-compaction --validate-asm --opt --no-always-opt
 //
 // /v8/test/mjsunit/wasm/grow-memory.js
 // /v8/test/mjsunit/regress/regress-540.js

test/mjsunit/regress/wasm/regress-02862.js

@@ -2,7 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-// Flags: --random-seed=1557792826 --expose-gc --invoke-weak-callbacks --omit-quit --gc-interval=469 --validate-asm
+// Flags:  --expose-gc --invoke-weak-callbacks --omit-quit --gc-interval=469 --validate-asm
 
 function nop() {}
 var __v_42 = {};

test/mjsunit/regress/wasm/regress-666741.js

@@ -2,7 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 //
-// Flags: --random-seed=-1101427159 --enable-slow-asserts --expose-wasm
+// Flags: --enable-slow-asserts --expose-wasm
 
 (function __f_7() {
   assertThrows(() => new WebAssembly.Memory({initial: 59199}), RangeError);

test/mjsunit/string-case.js

@@ -25,8 +25,7 @@
 // (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 // OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 
-// Flags: --random-seed=17 --allow-natives-syntax
-// Flags: --expose-externalize-string
+// Flags: --allow-natives-syntax --expose-externalize-string
 
 assertEquals("ΚΟΣΜΟΣ ΚΟΣΜΟΣ".toLowerCase(), "κοσμος κοσμος");
 

test/mjsunit/wasm/tier-up-testing-flag.js

@@ -2,7 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-// Flags: --allow-natives-syntax --liftoff --no-future --no-wasm-tier-up
+// Flags: --allow-natives-syntax --liftoff --no-wasm-tier-up
 // Compile functions 0 and 2 with Turbofan, the rest with Liftoff:
 // Flags: --wasm-tier-mask-for-testing=5
 

tools/testrunner/local/variants.py

@@ -24,8 +24,7 @@ ALL_VARIANT_FLAGS = {
   # independent of JS optimizations, so we can combine those configs.
   "nooptimization": [["--no-opt", "--liftoff", "--no-wasm-tier-up"]],
   "slow_path": [["--force-slow-path"]],
-  "stress": [["--stress-opt", "--always-opt", "--no-liftoff",
-              "--stress-lazy-source-positions"]],
+  "stress": [["--stress-opt", "--no-liftoff", "--stress-lazy-source-positions"]],
   "stress_js_bg_compile_wasm_code_gc": [["--stress-background-compile",
                                          "--stress-wasm-code-gc"]],
   "stress_incremental_marking": [["--stress-incremental-marking"]],
@@ -40,6 +39,21 @@ ALL_VARIANT_FLAGS = {
   "top_level_await": [["--harmony-top-level-await"]],
 }
 
+# Flags that lead to a contradiction with the flags provided by the respective
+# variant. This depends on the flags specified in ALL_VARIANT_FLAGS and on the
+# implications defined in flag-definitions.h
+INCOMPATIBLE_FLAGS_PER_VARIANT = {
+  "assert_types": ["--no-assert-types"],
+  "jitless": ["--opt", "--liftoff", "--track-field-types", "--validate-asm"],
+  "no_wasm_traps": ["--wasm-trap-handler"],
+  "nooptimization": ["--opt", "--no-liftoff", "--predictable", "--wasm-tier-up"],
+  "slow_path": ["--no-force-slow-path"],
+  "stress_incremental_marking": ["--no-stress-incremental-marking"],
+  "stress_js_bg_compile_wasm_code_gc": ["--no-stress-background-compile"],
+  "stress": ["--always-opt", "--liftoff"],
+  "turboprop": ["--turbo-inlining", "--interrupt-budget=*", "--no-turboprop"],
+}
+
 SLOW_VARIANTS = set([
   'stress',
   'stress_snapshot',

tools/testrunner/objects/testcase.py

@@ -34,6 +34,7 @@ from ..outproc import base as outproc
 from ..local import command
 from ..local import statusfile
 from ..local import utils
+from ..local.variants import INCOMPATIBLE_FLAGS_PER_VARIANT
 
 FLAGS_PATTERN = re.compile(r"//\s+Flags:(.*)")
 
@@ -84,7 +85,8 @@ class TestCase(object):
 
     # Outcomes
     self._statusfile_outcomes = None
-    self.expected_outcomes = None
+    self._expected_outcomes = None
+    self._checked_flag_contradictions = False
     self._statusfile_flags = None
 
     self._prepare_outcomes()
@@ -116,7 +118,7 @@ class TestCase(object):
       outcomes = self.suite.statusfile.get_outcomes(self.name, self.variant)
       self._statusfile_outcomes = filter(not_flag, outcomes)
       self._statusfile_flags = filter(is_flag, outcomes)
-    self.expected_outcomes = (
+    self._expected_outcomes = (
       self._parse_status_file_outcomes(self._statusfile_outcomes))
 
   def _parse_status_file_outcomes(self, outcomes):
@@ -141,6 +143,30 @@ class TestCase(object):
       return outproc.OUTCOMES_FAIL
     return expected_outcomes or outproc.OUTCOMES_PASS
 
+  @property
+  def expected_outcomes(self):
+    if not self._checked_flag_contradictions:
+      self._checked_flag_contradictions = True
+
+      def normalize_flag(flag):
+        return flag.replace("_", "-").replace("--no-", "--no")
+
+      all_flags = [normalize_flag(flag) for flag in self._get_cmd_params()]
+
+      def has_flag(conflicting_flag):
+          conflicting_flag = normalize_flag(conflicting_flag)
+          if conflicting_flag in all_flags:
+            return True
+          if conflicting_flag.endswith("*"):
+            return any(flag.startswith(conflicting_flag[:-1]) for flag in all_flags)
+          return False
+
+      if self.variant in INCOMPATIBLE_FLAGS_PER_VARIANT:
+        for conflicting_flag in INCOMPATIBLE_FLAGS_PER_VARIANT[self.variant]:
+          if has_flag(conflicting_flag):
+            self._expected_outcomes = outproc.OUTCOMES_FAIL
+    return self._expected_outcomes
+
   @property
   def do_skip(self):
     return (statusfile.SKIP in self._statusfile_outcomes and