Revert "[ia32,root] Add indirect calls and jumps through virtual register"

This reverts commit 65070355.

Reason for revert: https://ci.chromium.org/p/v8/builders/luci.v8.ci/V8%20Linux%20-%20noi18n%20-%20debug/23308

Original change's description:
> [ia32,root] Add indirect calls and jumps through virtual register
> 
> This adds a temporary mechanism for isolate-independent calls and
> jumps.  The problem was that - as ia32 doesn't have a scratch register
> - Call and Jump cannot call through a register. This CL adds a
> so-called virtual register (= a pointer-sized field) on IsolateData.
> 
> The virtual register can be removed once pc-relative calls are
> implemented and all builtins have been embedded.
> 
> Bug: v8:6666
> Change-Id: I1f9d8a25643fad0b3919dd813dbe219d20fcc6bc
> Reviewed-on: https://chromium-review.googlesource.com/c/1282991
> Commit-Queue: Jakob Gruber <jgruber@chromium.org>
> Reviewed-by: Sigurd Schneider <sigurds@chromium.org>
> Reviewed-by: Igor Sheludko <ishell@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#56693}

TBR=sigurds@chromium.org,jgruber@chromium.org,ishell@chromium.org

Change-Id: I782651140eee3e75d57ad57d614a981e420fdfeb
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: v8:6666
Reviewed-on: https://chromium-review.googlesource.com/c/1283051Reviewed-by: Jakob Gruber <jgruber@chromium.org>
Commit-Queue: Jakob Gruber <jgruber@chromium.org>
Cr-Commit-Position: refs/heads/master@{#56694}

src/ia32/macro-assembler-ia32.cc

@@ -1891,20 +1891,15 @@ void TurboAssembler::CallCFunction(Register function, int num_arguments) {
 void TurboAssembler::Call(Handle<Code> code_object, RelocInfo::Mode rmode) {
   if (FLAG_embedded_builtins) {
     // TODO(jgruber): Pc-relative builtin-to-builtin calls.
-    if (root_array_available_ && ShouldGenerateIsolateIndependentCode() &&
-        Builtins::IsBuiltin(*code_object)) {
-      // Since we don't have a scratch register available we call through a
-      // so-called virtual register.
-      // TODO(v8:6666): Remove once pc-relative jumps are supported on ia32.
-      Assembler::AllowExplicitEbxAccessScope read_only_access(this);
-      Operand virtual_call_target_register(
-          kRootRegister,
-          IsolateData::kVirtualCallTargetRegisterOffset - kRootRegisterBias);
-      Move(virtual_call_target_register, Immediate(code_object));
-      add(virtual_call_target_register,
-          Immediate(Code::kHeaderSize - kHeapObjectTag));
-      call(virtual_call_target_register);
-      return;
+    if (root_array_available_ && options().isolate_independent_code) {
+      // TODO(jgruber): There's no scratch register on ia32. Any call that
+      // requires loading a code object from the builtins constant table must:
+      // 1) spill two scratch registers, 2) load the target into scratch1, 3)
+      // store the target into a virtual register on the isolate using scratch2,
+      // 4) restore both scratch registers, and finally 5) call through the
+      // virtual register. All affected call sites should vanish once all
+      // builtins are embedded on ia32.
+      UNREACHABLE();
     } else if (options().inline_offheap_trampolines) {
       int builtin_index = Builtins::kNoBuiltinId;
       if (isolate()->builtins()->IsBuiltinHandle(code_object, &builtin_index) &&
@@ -1926,20 +1921,15 @@ void TurboAssembler::Call(Handle<Code> code_object, RelocInfo::Mode rmode) {
 void TurboAssembler::Jump(Handle<Code> code_object, RelocInfo::Mode rmode) {
   if (FLAG_embedded_builtins) {
     // TODO(jgruber): Pc-relative builtin-to-builtin calls.
-    if (root_array_available_ && ShouldGenerateIsolateIndependentCode() &&
-        Builtins::IsBuiltin(*code_object)) {
-      // Since we don't have a scratch register available we call through a
-      // so-called virtual register.
-      // TODO(v8:6666): Remove once pc-relative jumps are supported on ia32.
-      Assembler::AllowExplicitEbxAccessScope read_only_access(this);
-      Operand virtual_call_target_register(
-          kRootRegister,
-          IsolateData::kVirtualCallTargetRegisterOffset - kRootRegisterBias);
-      Move(virtual_call_target_register, Immediate(code_object));
-      add(virtual_call_target_register,
-          Immediate(Code::kHeaderSize - kHeapObjectTag));
-      jmp(virtual_call_target_register);
-      return;
+    if (root_array_available_ && options().isolate_independent_code) {
+      // TODO(jgruber): There's no scratch register on ia32. Any call that
+      // requires loading a code object from the builtins constant table must:
+      // 1) spill two scratch registers, 2) load the target into scratch1, 3)
+      // store the target into a virtual register on the isolate using scratch2,
+      // 4) restore both scratch registers, and finally 5) call through the
+      // virtual register. All affected call sites should vanish once all
+      // builtins are embedded on ia32.
+      UNREACHABLE();
     } else if (options().inline_offheap_trampolines) {
       int builtin_index = Builtins::kNoBuiltinId;
       if (isolate()->builtins()->IsBuiltinHandle(code_object, &builtin_index) &&

src/isolate-data.h

@@ -39,8 +39,7 @@ class IsolateData final {
   V(kBuiltinsTableEndOffset, 0)                                           \
   /* magic_number_ */                                                     \
   V(kMagicNumberOffset, kIntptrSize)                                      \
-  /* virtual_call_target_register_ */                                     \
-  V(kVirtualCallTargetRegisterOffset, kPointerSize)                       \
+  V(kMagicNumberEndOffset, 0)                                             \
   /* Total size. */                                                       \
   V(kSize, 0)
 
@@ -80,10 +79,6 @@ class IsolateData final {
   // TODO(v8:6666): Remove once the root register is fully supported on ia32.
   const intptr_t magic_number_ = kRootRegisterSentinel;
 
-  // For isolate-independent calls on ia32.
-  // TODO(v8:6666): Remove once pc-relative jumps are supported on ia32.
-  void* virtual_call_target_register_ = nullptr;
-
   V8_INLINE static void AssertPredictableLayout();
 
   friend class Isolate;