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Fix IEEE 754 unordered comparison detection in x87 floating-point operations

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Fix SoftFloat IsNan - custom detection matches IEEE754 semantics.
Sets Invalid Operation flags properly for NaN comparisons.

Fixes: GCC-C-execute-ieee-fp-cmp-8l test
__builtin_isunordered() now returns correct values for both NaN and normal operands
This commit is contained in:
Paulo Matos committed 2025-09-01 18:26:48 +02:00
1 parent f866ad52dc
commit 3d92c1fb32
2 files changed
+11 -1
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FEXCore/Source/Common/SoftFloat.h
+5 -1
View File
@@ -294,7 +294,11 @@ struct FEX_PACKED X80SoftFloat {
FCMP(softfloat_state* state, const X80SoftFloat& lhs, const X80SoftFloat& rhs, bool* eq, bool* lt, bool* nan) {
*eq = extF80_eq(state, lhs, rhs);
*lt = extF80_lt(state, lhs, rhs);
*nan = IsNan(lhs) || IsNan(rhs);
// Use IEEE 754 semantics: unordered if neither <, =, nor > is true
// This is more reliable than custom NaN detection
bool gt = !(*eq) && !(*lt) && extF80_le(state, rhs, lhs);
*nan = !(*eq) && !(*lt) && !gt;
}
FEXCORE_PRESERVE_ALL_ATTR static X80SoftFloat FSCALE(softfloat_state* state, const X80SoftFloat& lhs, const X80SoftFloat& rhs) {
FEXCore/Source/Interface/Core/OpcodeDispatcher/X87.cpp
+6
View File
@@ -680,6 +680,9 @@ void OpDispatchBuilder::FCOMI(OpcodeArgs, IR::OpSize Width, bool Integer, OpDisp
SetRFLAG<FEXCore::X86State::RFLAG_PF_RAW_LOC>(PF);
}
// Set Invalid Operation flag when unordered (NaN comparison)
SetRFLAG<FEXCore::X86State::X87FLAG_IE_LOC>(HostFlag_Unordered);
if (PopTwice) {
_PopStackDestroy();
_PopStackDestroy();
@@ -701,6 +704,9 @@ void OpDispatchBuilder::FTST(OpcodeArgs) {
SetRFLAG<FEXCore::X86State::X87FLAG_C1_LOC>(Constant(0));
SetRFLAG<FEXCore::X86State::X87FLAG_C2_LOC>(HostFlag_Unordered);
SetRFLAG<FEXCore::X86State::X87FLAG_C3_LOC>(HostFlag_ZF);
// Set Invalid Operation flag when unordered (NaN comparison)
SetRFLAG<FEXCore::X86State::X87FLAG_IE_LOC>(HostFlag_Unordered);
}
void OpDispatchBuilder::X87OpHelper(OpcodeArgs, FEXCore::IR::IROps IROp, bool ZeroC2) {