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[wasm] Fix I32ReinterpretF32 and I64ReinterpretF64 on ia32.

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On ia32 return statements in C++ automatically convert signalling NaNs
to quiet NaNs, even when bit_cast is used. This CL removes all uses of
bit_cast<float> and bit_cast<double> in the wasm compiler and wasm
interpreter.

R=titzer@chromium.org, clemensh@chromium.org

Review-Url: https://codereview.chromium.org/2639353002
Cr-Commit-Position: refs/heads/master@{#42512}
This commit is contained in:
ahaas 2017-01-19 08:21:02 -08:00 committed by Commit bot
parent ca0f957329
commit 7739affa5b
7 changed files with 72 additions and 16 deletions
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4
src/compiler/ia32/code-generator-ia32.cc
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@ -2106,7 +2106,7 @@ void CodeGenerator::AssembleMove(InstructionOperand* source,
__ Move(dst, g.ToImmediate(source));
} else if (src_constant.type() == Constant::kFloat32) {
// TODO(turbofan): Can we do better here?
uint32_t src = bit_cast<uint32_t>(src_constant.ToFloat32());
uint32_t src = src_constant.ToFloat32AsInt();
if (destination->IsFPRegister()) {
XMMRegister dst = g.ToDoubleRegister(destination);
__ Move(dst, src);
@ -2117,7 +2117,7 @@ void CodeGenerator::AssembleMove(InstructionOperand* source,
}
} else {
DCHECK_EQ(Constant::kFloat64, src_constant.type());
uint64_t src = bit_cast<uint64_t>(src_constant.ToFloat64());
uint64_t src = src_constant.ToFloat64AsInt();
uint32_t lower = static_cast<uint32_t>(src);
uint32_t upper = static_cast<uint32_t>(src >> 32);
if (destination->IsFPRegister()) {

17
src/compiler/instruction.h
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@ -1065,16 +1065,33 @@ class V8_EXPORT_PRIVATE Constant final {
}
float ToFloat32() const {
// TODO(ahaas): We should remove this function. If value_ has the bit
// representation of a signalling NaN, then returning it as float can cause
// the signalling bit to flip, and value_ is returned as a quiet NaN.
DCHECK_EQ(kFloat32, type());
return bit_cast<float>(static_cast<int32_t>(value_));
}
uint32_t ToFloat32AsInt() const {
DCHECK_EQ(kFloat32, type());
return bit_cast<uint32_t>(static_cast<int32_t>(value_));
}
double ToFloat64() const {
// TODO(ahaas): We should remove this function. If value_ has the bit
// representation of a signalling NaN, then returning it as float can cause
// the signalling bit to flip, and value_ is returned as a quiet NaN.
if (type() == kInt32) return ToInt32();
DCHECK_EQ(kFloat64, type());
return bit_cast<double>(value_);
}
uint64_t ToFloat64AsInt() const {
if (type() == kInt32) return ToInt32();
DCHECK_EQ(kFloat64, type());
return bit_cast<uint64_t>(value_);
}
ExternalReference ToExternalReference() const {
DCHECK_EQ(kExternalReference, type());
return bit_cast<ExternalReference>(static_cast<intptr_t>(value_));

8
src/wasm/function-body-decoder.h
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@ -70,7 +70,9 @@ struct ImmF32Operand {
float value;
unsigned length;
inline ImmF32Operand(Decoder* decoder, const byte* pc) {
value = bit_cast<float>(decoder->checked_read_u32(pc, 1, "immf32"));
// Avoid bit_cast because it might not preserve the signalling bit of a NaN.
uint32_t tmp = decoder->checked_read_u32(pc, 1, "immf32");
value = *reinterpret_cast<float*>(&tmp);
length = 4;
}
};
@ -79,7 +81,9 @@ struct ImmF64Operand {
double value;
unsigned length;
inline ImmF64Operand(Decoder* decoder, const byte* pc) {
value = bit_cast<double>(decoder->checked_read_u64(pc, 1, "immf64"));
// Avoid bit_cast because it might not preserve the signalling bit of a NaN.
uint64_t tmp = decoder->checked_read_u64(pc, 1, "immf64");
value = *reinterpret_cast<double*>(&tmp);
length = 8;
}
};

23
src/wasm/wasm-interpreter.cc
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@ -159,8 +159,6 @@ namespace wasm {
V(F64UConvertI64, uint64_t) \
V(F64ConvertF32, float) \
V(F64ReinterpretI64, int64_t) \
V(I32ReinterpretF32, float) \
V(I64ReinterpretF64, double) \
V(I32AsmjsSConvertF32, float) \
V(I32AsmjsUConvertF32, float) \
V(I32AsmjsSConvertF64, double) \
@ -606,12 +604,12 @@ static inline double ExecuteF64ReinterpretI64(int64_t a, TrapReason* trap) {
return bit_cast<double>(a);
}
static inline int32_t ExecuteI32ReinterpretF32(float a, TrapReason* trap) {
return bit_cast<int32_t>(a);
static inline int32_t ExecuteI32ReinterpretF32(WasmVal a) {
return a.to_unchecked<int32_t>();
}
static inline int64_t ExecuteI64ReinterpretF64(double a, TrapReason* trap) {
return bit_cast<int64_t>(a);
static inline int64_t ExecuteI64ReinterpretF64(WasmVal a) {
return a.to_unchecked<int64_t>();
}
static inline int32_t ExecuteGrowMemory(uint32_t delta_pages,
@ -1548,6 +1546,19 @@ class ThreadImpl {
len = 1 + operand.length;
break;
}
// We need to treat kExprI32ReinterpretF32 and kExprI64ReinterpretF64
// specially to guarantee that the quiet bit of a NaN is preserved on
// ia32 by the reinterpret casts.
case kExprI32ReinterpretF32: {
WasmVal result(ExecuteI32ReinterpretF32(Pop()));
Push(pc, result);
break;
}
case kExprI64ReinterpretF64: {
WasmVal result(ExecuteI64ReinterpretF64(Pop()));
Push(pc, result);
break;
}
#define EXECUTE_SIMPLE_BINOP(name, ctype, op) \
case kExpr##name: { \
WasmVal rval = Pop(); \

16
src/wasm/wasm-interpreter.h
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@ -56,12 +56,21 @@ struct WasmVal {
#undef DECLARE_CONSTRUCTOR
template <typename T>
T to() {
inline T to() {
UNREACHABLE();
}
template <typename T>
inline T to_unchecked() {
UNREACHABLE();
}
};
#define DECLARE_CAST(field, localtype, ctype) \
template <> \
inline ctype WasmVal::to_unchecked() { \
return val.field; \
} \
template <> \
inline ctype WasmVal::to() { \
CHECK_EQ(localtype, type); \
@ -70,11 +79,6 @@ struct WasmVal {
FOREACH_UNION_MEMBER(DECLARE_CAST)
#undef DECLARE_CAST
template <>
inline void WasmVal::to() {
CHECK_EQ(kWasmStmt, type);
}
// Representation of frames within the interpreter.
class WasmFrame {
public:

10
test/cctest/wasm/test-run-wasm-64.cc
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@ -1319,6 +1319,16 @@ WASM_EXEC_TEST(I64ReinterpretF64) {
}
}
WASM_EXEC_TEST(SignallingNanSurvivesI64ReinterpretF64) {
REQUIRE(I64ReinterpretF64);
WasmRunner<int64_t> r(execution_mode);
BUILD(r, WASM_I64_REINTERPRET_F64(WASM_SEQ(kExprF64Const, 0x00, 0x00, 0x00,
0x00, 0x00, 0x00, 0xf4, 0x7f)));
// This is a signalling nan.
CHECK_EQ(0x7ff4000000000000, r.Call());
}
WASM_EXEC_TEST(F64ReinterpretI64) {
REQUIRE(F64ReinterpretI64);
WasmRunner<int64_t, int64_t> r(execution_mode);

10
test/cctest/wasm/test-run-wasm.cc
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@ -1048,6 +1048,16 @@ WASM_EXEC_TEST(I32ReinterpretF32) {
}
}
WASM_EXEC_TEST(SignallingNanSurvivesI32ReinterpretF32) {
WasmRunner<int32_t> r(execution_mode);
BUILD(r, WASM_I32_REINTERPRET_F32(
WASM_SEQ(kExprF32Const, 0x00, 0x00, 0xa0, 0x7f)));
// This is a signalling nan.
CHECK_EQ(0x7fa00000, r.Call());
}
WASM_EXEC_TEST_WITH_TRAP(LoadMaxUint32Offset) {
WasmRunner<int32_t> r(execution_mode);
r.module().AddMemoryElems<int32_t>(8);