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Arm64: Remove forced csp alignment to 16 byte values for Nvidia chips.

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Remove the forced alignment of csp to 16 byte values on Nvidia chips.
Benchmarks on current devices show that this is no longer required.

R=rodolph.perfetta@arm.com, ulan@chromium.org

Review URL: https://codereview.chromium.org/710613002

Cr-Commit-Position: refs/heads/master@{#25225}
git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@25225 ce2b1a6d-e550-0410-aec6-3dcde31c8c00
This commit is contained in:
rmcilroy@chromium.org 2014-11-07 23:34:13 +00:00
parent c24ebcd387
commit 49d1f64ebf
6 changed files with 15 additions and 50 deletions
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13
src/arm64/assembler-arm64.cc
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@ -44,17 +44,8 @@ namespace internal {
// CpuFeatures implementation.
void CpuFeatures::ProbeImpl(bool cross_compile) {
if (cross_compile) {
// Always align csp in cross compiled code - this is safe and ensures that
// csp will always be aligned if it is enabled by probing at runtime.
if (FLAG_enable_always_align_csp) supported_ |= 1u << ALWAYS_ALIGN_CSP;
} else {
base::CPU cpu;
if (FLAG_enable_always_align_csp &&
(cpu.implementer() == base::CPU::NVIDIA || FLAG_debug_code)) {
supported_ |= 1u << ALWAYS_ALIGN_CSP;
}
}
// AArch64 has no configuration options, no further probing is required.
supported_ = 0;
}

18
src/arm64/code-stubs-arm64.cc
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@ -4334,18 +4334,10 @@ void KeyedLoadICTrampolineStub::Generate(MacroAssembler* masm) {
}
static unsigned int GetProfileEntryHookCallSize(MacroAssembler* masm) {
// The entry hook is a "BumpSystemStackPointer" instruction (sub),
// followed by a "Push lr" instruction, followed by a call.
unsigned int size =
// The entry hook is a "BumpSystemStackPointer" instruction (sub), followed by
// a "Push lr" instruction, followed by a call.
static const unsigned int kProfileEntryHookCallSize =
Assembler::kCallSizeWithRelocation + (2 * kInstructionSize);
if (CpuFeatures::IsSupported(ALWAYS_ALIGN_CSP)) {
// If ALWAYS_ALIGN_CSP then there will be an extra bic instruction in
// "BumpSystemStackPointer".
size += kInstructionSize;
}
return size;
}
void ProfileEntryHookStub::MaybeCallEntryHook(MacroAssembler* masm) {
@ -4358,7 +4350,7 @@ void ProfileEntryHookStub::MaybeCallEntryHook(MacroAssembler* masm) {
__ Push(lr);
__ CallStub(&stub);
DCHECK(masm->SizeOfCodeGeneratedSince(&entry_hook_call_start) ==
GetProfileEntryHookCallSize(masm));
kProfileEntryHookCallSize);
__ Pop(lr);
}
@ -4376,7 +4368,7 @@ void ProfileEntryHookStub::Generate(MacroAssembler* masm) {
const int kNumSavedRegs = kCallerSaved.Count();
// Compute the function's address as the first argument.
__ Sub(x0, lr, GetProfileEntryHookCallSize(masm));
__ Sub(x0, lr, kProfileEntryHookCallSize);
#if V8_HOST_ARCH_ARM64
uintptr_t entry_hook =

11
src/arm64/macro-assembler-arm64-inl.h
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@ -1244,14 +1244,7 @@ void MacroAssembler::Uxtw(const Register& rd, const Register& rn) {
void MacroAssembler::BumpSystemStackPointer(const Operand& space) {
DCHECK(!csp.Is(sp_));
if (!TmpList()->IsEmpty()) {
if (CpuFeatures::IsSupported(ALWAYS_ALIGN_CSP)) {
UseScratchRegisterScope temps(this);
Register temp = temps.AcquireX();
Sub(temp, StackPointer(), space);
Bic(csp, temp, 0xf);
} else {
Sub(csp, StackPointer(), space);
}
} else {
// TODO(jbramley): Several callers rely on this not using scratch
// registers, so we use the assembler directly here. However, this means
@ -1288,12 +1281,8 @@ void MacroAssembler::SyncSystemStackPointer() {
DCHECK(emit_debug_code());
DCHECK(!csp.Is(sp_));
{ InstructionAccurateScope scope(this);
if (CpuFeatures::IsSupported(ALWAYS_ALIGN_CSP)) {
bic(csp, StackPointer(), 0xf);
} else {
mov(csp, StackPointer());
}
}
AssertStackConsistency();
}

2
src/arm64/macro-assembler-arm64.cc
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@ -1308,7 +1308,7 @@ void MacroAssembler::AssertStackConsistency() {
// Avoid emitting code when !use_real_abort() since non-real aborts cause too
// much code to be generated.
if (emit_debug_code() && use_real_aborts()) {
if (csp.Is(StackPointer()) || CpuFeatures::IsSupported(ALWAYS_ALIGN_CSP)) {
if (csp.Is(StackPointer())) {
// Always check the alignment of csp if ALWAYS_ALIGN_CSP is true. We
// can't check the alignment of csp without using a scratch register (or
// clobbering the flags), but the processor (or simulator) will abort if

10
src/arm64/macro-assembler-arm64.h
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@ -761,9 +761,9 @@ class MacroAssembler : public Assembler {
// it can be evidence of a potential bug because the ABI forbids accesses
// below csp.
//
// If StackPointer() is the system stack pointer (csp) or ALWAYS_ALIGN_CSP is
// enabled, then csp will be dereferenced to cause the processor
// (or simulator) to abort if it is not properly aligned.
// If StackPointer() is the system stack pointer (csp), then csp will be
// dereferenced to cause the processor (or simulator) to abort if it is not
// properly aligned.
//
// If emit_debug_code() is false, this emits no code.
void AssertStackConsistency();
@ -831,9 +831,7 @@ class MacroAssembler : public Assembler {
inline void BumpSystemStackPointer(const Operand& space);
// Re-synchronizes the system stack pointer (csp) with the current stack
// pointer (according to StackPointer()). This function will ensure the
// new value of the system stack pointer is remains aligned to 16 bytes, and
// is lower than or equal to the value of the current stack pointer.
// pointer (according to StackPointer()).
//
// This method asserts that StackPointer() is not csp, since the call does
// not make sense in that context.

5
src/flag-definitions.h
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@ -438,11 +438,6 @@ DEFINE_BOOL(enable_vldr_imm, false,
DEFINE_BOOL(force_long_branches, false,
"force all emitted branches to be in long mode (MIPS only)")
// cpu-arm64.cc
DEFINE_BOOL(enable_always_align_csp, true,
"enable alignment of csp to 16 bytes on platforms which prefer "
"the register to always be aligned (ARM64 only)")
// bootstrapper.cc
DEFINE_STRING(expose_natives_as, NULL, "expose natives in global object")
DEFINE_STRING(expose_debug_as, NULL, "expose debug in global object")