[wasm] Remove Result::MoveErrorFrom

This is the last method which modified the Result after construction.
Turn this into a named constructor instead.

Drive-by: Replace a Result<bool> by VoidResult, since the bool is not
used anywhere.

R=mstarzinger@chromium.org

Bug: v8:8238
Change-Id: I352e0687e99a90e6ad00587d6fdf388f68c9b60a
Reviewed-on: https://chromium-review.googlesource.com/c/1296271
Commit-Queue: Clemens Hammacher <clemensh@chromium.org>
Reviewed-by: Michael Starzinger <mstarzinger@chromium.org>
Cr-Commit-Position: refs/heads/master@{#56897}

src/compiler/wasm-compiler.cc

@@ -5165,7 +5165,8 @@ SourcePositionTable* TurbofanWasmCompilationUnit::BuildGraphForWasmFunction(
       StdoutStream{} << "Compilation failed: "
                      << graph_construction_result.error_msg() << std::endl;
     }
-    wasm_unit_->result_.MoveErrorFrom(graph_construction_result);
+    wasm_unit_->result_ = wasm::Result<wasm::WasmCode*>::ErrorFrom(
+        std::move(graph_construction_result));
     return nullptr;
   }
 

src/wasm/module-compiler.cc

@@ -2641,14 +2641,14 @@ AsyncStreamingProcessor::AsyncStreamingProcessor(AsyncCompileJob* job)
       compilation_unit_builder_(nullptr) {}
 
 void AsyncStreamingProcessor::FinishAsyncCompileJobWithError(ResultBase error) {
+  DCHECK(error.failed());
   // Make sure all background tasks stopped executing before we change the state
   // of the AsyncCompileJob to DecodeFail.
   job_->background_task_manager_.CancelAndWait();
 
   // Create a ModuleResult from the result we got as parameter. Since there was
-  // no error, we don't have to provide a real wasm module to the ModuleResult.
-  ModuleResult result(nullptr);
-  result.MoveErrorFrom(error);
+  // an error, we don't have to provide a real wasm module to the ModuleResult.
+  ModuleResult result = ModuleResult::ErrorFrom(std::move(error));
 
   // Check if there is already a CompiledModule, in which case we have to clean
   // up the CompilationState as well.

src/wasm/module-decoder.cc

@@ -906,9 +906,9 @@ class ModuleDecoderImpl : public Decoder {
       CalculateGlobalOffsets(module_.get());
     }
     ModuleResult result = toResult(std::move(module_));
-    if (verify_functions && result.ok()) {
+    if (verify_functions && result.ok() && intermediate_result_.failed()) {
       // Copy error code and location.
-      result.MoveErrorFrom(intermediate_result_);
+      result = ModuleResult::ErrorFrom(std::move(intermediate_result_));
     }
     return result;
   }
@@ -963,10 +963,11 @@ class ModuleDecoderImpl : public Decoder {
       VerifyFunctionBody(zone->allocator(), 0, wire_bytes, module,
                          function.get());
 
-    FunctionResult result(std::move(function));
-    // Copy error code and location.
-    result.MoveErrorFrom(intermediate_result_);
-    return result;
+    if (intermediate_result_.failed()) {
+      return FunctionResult::ErrorFrom(std::move(intermediate_result_));
+    }
+
+    return FunctionResult(std::move(function));
   }
 
   // Decodes a single function signature at {start}.
@@ -1010,7 +1011,7 @@ class ModuleDecoderImpl : public Decoder {
                         sizeof(ModuleDecoderImpl::seen_unordered_sections_) >
                     kLastKnownModuleSection,
                 "not enough bits");
-  Result<bool> intermediate_result_;
+  VoidResult intermediate_result_;
   ModuleOrigin origin_;
 
   uint32_t off(const byte* ptr) {
@@ -1128,16 +1129,14 @@ class ModuleDecoderImpl : public Decoder {
                               &unused_detected_features, body);
     }
 
-    if (result.failed()) {
+    // If the decode failed and this is the first error, set error code and
+    // location.
+    if (result.failed() && intermediate_result_.ok()) {
       // Wrap the error message from the function decoder.
-      std::ostringstream wrapped;
-      wrapped << "in function " << func_name << ": " << result.error_msg();
-      result = DecodeResult::Error(result.error_offset(), wrapped.str());
-
-      // Set error code and location, if this is the first error.
-      if (intermediate_result_.ok()) {
-        intermediate_result_.MoveErrorFrom(result);
-      }
+      std::ostringstream error_msg;
+      error_msg << "in function " << func_name << ": " << result.error_msg();
+      intermediate_result_ =
+          VoidResult::Error(result.error_offset(), error_msg.str());
     }
   }
 

src/wasm/wasm-result.h

@@ -33,19 +33,12 @@ class V8_EXPORT_PRIVATE ResultBase {
       : error_offset_(other.error_offset_),
         error_msg_(std::move(other.error_msg_)) {}
 
-  void MoveErrorFrom(ResultBase& that) {
-    error_offset_ = that.error_offset_;
-    // Use {swap()} + {clear()} instead of move assign, as {that} might still
-    // be used afterwards.
-    error_msg_.swap(that.error_msg_);
-    that.error_msg_.clear();
-  }
-
   bool ok() const { return error_msg_.empty(); }
   bool failed() const { return !ok(); }
 
   uint32_t error_offset() const { return error_offset_; }
-  const std::string& error_msg() const { return error_msg_; }
+  const std::string& error_msg() const & { return error_msg_; }
+  std::string&& error_msg() && { return std::move(error_msg_); }
 
  protected:
   ResultBase(uint32_t error_offset, std::string error_msg)
@@ -90,6 +83,11 @@ class Result : public ResultBase {
     return Result<T>{error_offset, std::move(error_msg)};
   }
 
+  static Result<T> ErrorFrom(ResultBase&& error_result) {
+    return Error(error_result.error_offset(),
+                 std::move(error_result).error_msg());
+  }
+
   // Accessor for the value. Returns const reference if {this} is l-value or
   // const, and returns r-value reference if {this} is r-value. This allows to
   // extract non-copyable values like {std::unique_ptr} by using