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deps: V8: partially cherry-pick 8953e49478 #55274

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deps: V8: partially cherry-pick 8953e49478 #55274

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deps: V8: partially cherry-pick 8953e49478 
Very partial cherry-pick of upstream commit v8/v8@8953e49478 that fixes
a hang that shows up in debug builds because of a buggy sanity check
when computing relationships between command line flags.

Example of the hang:

    #include "v8.h"
    #include "libplatform/libplatform.h"
    int main(void) {
      // works: v8::V8::SetFlagsFromString("--gc-global --noincremental-marking");
      v8::V8::SetFlagsFromString("--gc-global");
      v8::V8::SetFlagsFromString("--noincremental-marking");
      v8::V8::InitializePlatform(v8::platform::NewDefaultPlatform().release());
      v8::V8::Initialize(); // hangs in ComputeFlagListHash when defined(DEBUG)
    }
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@bnoordhuis
bnoordhuis committed Oct 5, 2024
commit 9c9b416093b9543e7c3d33005759d75519f84c60
5 changes: 5 additions & 0 deletions deps/v8/src/flags/flags-impl.h
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Original file line number Diff line number Diff line change
Expand Up @@ -5,6 +5,8 @@
#ifndef V8_FLAGS_FLAGS_IMPL_H_
#define V8_FLAGS_FLAGS_IMPL_H_

#include <unordered_set>

#include "src/base/macros.h"
#include "src/base/optional.h"
#include "src/base/vector.h"
Expand Down Expand Up @@ -91,9 +93,12 @@ struct Flag {
#ifdef DEBUG
bool ImpliedBy(const void* ptr) const {
const Flag* current = this->implied_by_ptr_;
std::unordered_set<const Flag*> visited_flags;
while (current != nullptr) {
visited_flags.insert(current);
if (current->PointsTo(ptr)) return true;
current = current->implied_by_ptr_;
if (visited_flags.contains(current)) break;
}
return false;
}
Expand Down