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[Liftoff] Only allocate Labels on the heap on arm64

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Arm64 is the only platform where Labels cannot be moved, because the
assembler keeps track of pointers to Labels. On all other platforms,
there is no need to heap-allocate the Labels.

R=titzer@chromium.org

Bug: v8:6600
Change-Id: I4e98203890a8c426afa8a1db21e31f30bab892fa
Reviewed-on: https://chromium-review.googlesource.com/783210
Reviewed-by: Ben Titzer <titzer@chromium.org>
Commit-Queue: Clemens Hammacher <clemensh@chromium.org>
Cr-Commit-Position: refs/heads/master@{#49572}
This commit is contained in:
Clemens Hammacher 2017-11-22 12:13:51 +01:00 committed by Commit Bot
parent 4d70aa02fd
commit 09bf6c1c2f
1 changed files with 24 additions and 4 deletions
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28
src/wasm/baseline/liftoff-compiler.cc
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@ -30,6 +30,28 @@ namespace {
if (FLAG_trace_liftoff) PrintF("[liftoff] " __VA_ARGS__); \
} while (false)
#if V8_TARGET_ARCH_ARM64
// On ARM64, the Assembler keeps track of pointers to Labels to resolve
// branches to distant targets. Moving labels would confuse the Assembler,
// thus store the label on the heap and keep a unique_ptr.
class MovableLabel {
public:
Label* get() { return label_.get(); }
private:
std::unique_ptr<Label> label_ = base::make_unique<Label>();
};
#else
// On all other platforms, just store the Label directly.
class MovableLabel {
public:
Label* get() { return &label_; }
private:
Label label_;
};
#endif
class LiftoffCompiler {
public:
MOVE_ONLY_NO_DEFAULT_CONSTRUCTOR(LiftoffCompiler);
@ -44,9 +66,7 @@ class LiftoffCompiler {
MOVE_ONLY_WITH_DEFAULT_CONSTRUCTORS(Control);
LiftoffAssembler::CacheState label_state;
// TODO(clemensh): Labels cannot be moved on arm64, but everywhere else.
// Find a better solution.
std::unique_ptr<Label> label = base::make_unique<Label>();
MovableLabel label;
};
using Decoder = WasmFullDecoder<validate, LiftoffCompiler>;
@ -206,7 +226,7 @@ class LiftoffCompiler {
if (!c->is_loop() && c->end_merge.reached) {
__ cache_state()->Steal(c->label_state);
}
if (!c->label->is_bound()) {
if (!c->label.get()->is_bound()) {
__ bind(c->label.get());
}
}