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[Liftoff] Optimize code for returns

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Since all other values are not used any more if we return, we don't
need to spill anything (as might happen during {PopToRegister}).
Instead, just load the top stack value into the return register(s).

R=titzer@chromium.org

Bug: v8:6600, v8:8423
Change-Id: Ibfd02d20191459c7b136ab9a48f0cf1a53b3385d
Reviewed-on: https://chromium-review.googlesource.com/c/1358391
Commit-Queue: Clemens Hammacher <clemensh@chromium.org>
Reviewed-by: Ben Titzer <titzer@chromium.org>
Cr-Commit-Position: refs/heads/master@{#57995}
This commit is contained in:
Clemens Hammacher 2018-12-03 15:05:59 +01:00 committed by Commit Bot
parent 0ed8017e8a
commit 558c950454
3 changed files with 24 additions and 13 deletions
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17
src/wasm/baseline/liftoff-assembler.cc
View File

@ -11,6 +11,7 @@
#include "src/compiler/wasm-compiler.h"
#include "src/macro-assembler-inl.h"
#include "src/wasm/function-body-decoder-impl.h"
#include "src/wasm/wasm-linkage.h"
#include "src/wasm/wasm-opcodes.h"
namespace v8 {
@ -620,6 +621,22 @@ void LiftoffAssembler::ParallelRegisterMove(
}
}
void LiftoffAssembler::MoveToReturnRegisters(FunctionSig* sig) {
// We do not support multi-value yet.
DCHECK_EQ(1, sig->return_count());
ValueType return_type = sig->GetReturn(0);
StackTransferRecipe stack_transfers(this);
LiftoffRegister return_reg =
needs_reg_pair(return_type)
? LiftoffRegister::ForPair(kGpReturnRegisters[0],
kGpReturnRegisters[1])
: reg_class_for(return_type) == kGpReg
? LiftoffRegister(kGpReturnRegisters[0])
: LiftoffRegister(kFpReturnRegisters[0]);
stack_transfers.LoadIntoRegister(return_reg, cache_state_.stack_state.back(),
cache_state_.stack_height() - 1);
}
#ifdef ENABLE_SLOW_DCHECKS
bool LiftoffAssembler::ValidateCacheState() const {
uint32_t register_use_count[kAfterMaxLiftoffRegCode] = {0};

2
src/wasm/baseline/liftoff-assembler.h
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@ -338,6 +338,8 @@ class LiftoffAssembler : public TurboAssembler {
};
void ParallelRegisterMove(Vector<ParallelRegisterMoveTuple>);
void MoveToReturnRegisters(FunctionSig*);
#ifdef ENABLE_SLOW_DCHECKS
// Validate that the register use counts reflect the state of the cache.
bool ValidateCacheState() const;

18
src/wasm/baseline/liftoff-compiler.cc
View File

@ -1075,25 +1075,17 @@ class LiftoffCompiler {
__ cache_state()->stack_state.pop_back();
}
void DoReturn(FullDecoder* decoder, Vector<Value> values, bool implicit) {
void DoReturn(FullDecoder* decoder, Vector<Value> /*values*/, bool implicit) {
if (implicit) {
DCHECK_EQ(1, decoder->control_depth());
Control* func_block = decoder->control_at(0);
__ bind(func_block->label.get());
__ cache_state()->Steal(func_block->label_state);
TraceCacheState(decoder);
}
if (!values.is_empty()) {
if (values.size() > 1) return unsupported(decoder, "multi-return");
LiftoffRegister reg = __ PopToRegister();
LiftoffRegister return_reg =
kNeedI64RegPair && values[0].type == kWasmI64
? LiftoffRegister::ForPair(kGpReturnRegisters[0],
kGpReturnRegisters[1])
: reg_class_for(values[0].type) == kGpReg
? LiftoffRegister(kGpReturnRegisters[0])
: LiftoffRegister(kFpReturnRegisters[0]);
if (reg != return_reg) __ Move(return_reg, reg, values[0].type);
}
size_t num_returns = decoder->sig_->return_count();
if (num_returns > 1) return unsupported(decoder, "multi-return");
if (num_returns > 0) __ MoveToReturnRegisters(decoder->sig_);
__ LeaveFrame(StackFrame::WASM_COMPILED);
__ DropStackSlotsAndRet(
static_cast<uint32_t>(descriptor_->StackParameterCount()));