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[X86] Don't rely on global contraction flag #167252

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Merged
merged 8 commits into from
Nov 13, 2025
Merged

[X86] Don't rely on global contraction flag #167252

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b8dcc44
Make X86 backend not rely on global contract flag
mikolaj-pirog Nov 9, 2025
591d77e
Formatting
mikolaj-pirog Nov 9, 2025
2279803
remove unused
mikolaj-pirog Nov 9, 2025
22ff3fd
Reviewer suggestions
mikolaj-pirog Nov 10, 2025
c8ce070
Formatting
mikolaj-pirog Nov 10, 2025
cef9fa0
Add warning on using fp-contract on x86
mikolaj-pirog Nov 12, 2025
52fd57b
Add test, fix last test using fp-contract=fast
mikolaj-pirog Nov 12, 2025
59e4ae7
Add missing contract
mikolaj-pirog Nov 13, 2025
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14 changes: 3 additions & 11 deletions llvm/lib/Target/X86/X86ISelLowering.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -8432,9 +8432,7 @@ static bool isFMAddSubOrFMSubAdd(const X86Subtarget &Subtarget,
// DAGCombiner::visitFADDForFMACombine. It would be good to have one
// function that would answer if it is Ok to fuse MUL + ADD to FMADD
// or MUL + ADDSUB to FMADDSUB.
const TargetOptions &Options = DAG.getTarget().Options;
bool AllowFusion =
Options.AllowFPOpFusion == FPOpFusion::Fast ||
(AllowSubAddOrAddSubContract && Opnd0->getFlags().hasAllowContract());
if (!AllowFusion)
return false;
Expand Down Expand Up @@ -54160,11 +54158,6 @@ static SDValue combineFMulcFCMulc(SDNode *N, SelectionDAG &DAG,
// FADD(A, FMA(B, C, 0)) and FADD(A, FMUL(B, C)) to FMA(B, C, A)
static SDValue combineFaddCFmul(SDNode *N, SelectionDAG &DAG,
const X86Subtarget &Subtarget) {
auto AllowContract = [&DAG](const SDNodeFlags &Flags) {
return DAG.getTarget().Options.AllowFPOpFusion == FPOpFusion::Fast ||
Flags.hasAllowContract();
};

auto HasNoSignedZero = [&DAG](const SDNodeFlags &Flags) {
return DAG.getTarget().Options.NoSignedZerosFPMath ||
Flags.hasNoSignedZeros();
Expand All @@ -54177,7 +54170,7 @@ static SDValue combineFaddCFmul(SDNode *N, SelectionDAG &DAG,
};

if (N->getOpcode() != ISD::FADD || !Subtarget.hasFP16() ||
!AllowContract(N->getFlags()))
!N->getFlags().hasAllowContract())
return SDValue();

EVT VT = N->getValueType(0);
Expand All @@ -54188,14 +54181,13 @@ static SDValue combineFaddCFmul(SDNode *N, SelectionDAG &DAG,
SDValue RHS = N->getOperand(1);
bool IsConj;
SDValue FAddOp1, MulOp0, MulOp1;
auto GetCFmulFrom = [&MulOp0, &MulOp1, &IsConj, &AllowContract,
&IsVectorAllNegativeZero,
auto GetCFmulFrom = [&MulOp0, &MulOp1, &IsConj, &IsVectorAllNegativeZero,
&HasNoSignedZero](SDValue N) -> bool {
if (!N.hasOneUse() || N.getOpcode() != ISD::BITCAST)
return false;
SDValue Op0 = N.getOperand(0);
unsigned Opcode = Op0.getOpcode();
if (Op0.hasOneUse() && AllowContract(Op0->getFlags())) {
if (Op0.hasOneUse() && Op0->getFlags().hasAllowContract()) {
if ((Opcode == X86ISD::VFMULC || Opcode == X86ISD::VFCMULC)) {
MulOp0 = Op0.getOperand(0);
MulOp1 = Op0.getOperand(1);
Expand Down
12 changes: 12 additions & 0 deletions llvm/test/CodeGen/X86/llc-fp-contract-warning.ll
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@@ -0,0 +1,12 @@
; RUN: llc < %s -mtriple=x86_64-unknown-unknown --fp-contract=fast 2>&1 | grep "X86 backend ignores --fp-contract"

; RUN: llc < %s -mtriple=x86_64-unknown-unknown --fp-contract=off 2>&1 | grep "X86 backend ignores --fp-contract"

; on, as a default setting that's passed to backend when no --fp-contract option is specified, is not diagnosed.
; RUN: llc < %s -mtriple=x86_64-unknown-unknown --fp-contract=on 2>&1 | grep -v "X86 backend ignores --fp-contract"

define float @foo(float %f) {
%res = fadd float %f, %f
ret float %res
}

40 changes: 21 additions & 19 deletions llvm/test/CodeGen/X86/sqrt-fastmath-mir.ll
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Original file line number Diff line number Diff line change
@@ -1,5 +1,5 @@
; NOTE: Assertions have been autogenerated by utils/update_mir_test_checks.py
; RUN: llc -fp-contract=fast < %s -mtriple=x86_64-unknown-unknown -mattr=avx2,fma -stop-after=finalize-isel 2>&1 | FileCheck %s
; RUN: llc < %s -mtriple=x86_64-unknown-unknown -mattr=avx2,fma -stop-after=finalize-isel 2>&1 | FileCheck %s

declare float @llvm.sqrt.f32(float) #2

Expand All @@ -24,17 +24,17 @@ define float @sqrt_ieee_ninf(float %f) #0 {
; CHECK-NEXT: {{ $}}
; CHECK-NEXT: [[COPY:%[0-9]+]]:fr32 = COPY $xmm0
; CHECK-NEXT: [[DEF:%[0-9]+]]:fr32 = IMPLICIT_DEF
; CHECK-NEXT: [[VRSQRTSSr:%[0-9]+]]:fr32 = ninf afn VRSQRTSSr killed [[DEF]], [[COPY]]
; CHECK-NEXT: [[VMULSSrr:%[0-9]+]]:fr32 = ninf afn nofpexcept VMULSSrr [[COPY]], [[VRSQRTSSr]], implicit $mxcsr
; CHECK-NEXT: [[VRSQRTSSr:%[0-9]+]]:fr32 = ninf contract afn VRSQRTSSr killed [[DEF]], [[COPY]]
; CHECK-NEXT: [[VMULSSrr:%[0-9]+]]:fr32 = ninf contract afn nofpexcept VMULSSrr [[COPY]], [[VRSQRTSSr]], implicit $mxcsr
; CHECK-NEXT: [[VMOVSSrm_alt:%[0-9]+]]:fr32 = VMOVSSrm_alt $rip, 1, $noreg, %const.0, $noreg :: (load (s32) from constant-pool)
; CHECK-NEXT: [[VFMADD213SSr:%[0-9]+]]:fr32 = ninf afn nofpexcept VFMADD213SSr [[VRSQRTSSr]], killed [[VMULSSrr]], [[VMOVSSrm_alt]], implicit $mxcsr
; CHECK-NEXT: [[VFMADD213SSr:%[0-9]+]]:fr32 = ninf contract afn nofpexcept VFMADD213SSr [[VRSQRTSSr]], killed [[VMULSSrr]], [[VMOVSSrm_alt]], implicit $mxcsr
; CHECK-NEXT: [[VMOVSSrm_alt1:%[0-9]+]]:fr32 = VMOVSSrm_alt $rip, 1, $noreg, %const.1, $noreg :: (load (s32) from constant-pool)
; CHECK-NEXT: [[VMULSSrr1:%[0-9]+]]:fr32 = ninf afn nofpexcept VMULSSrr [[VRSQRTSSr]], [[VMOVSSrm_alt1]], implicit $mxcsr
; CHECK-NEXT: [[VMULSSrr2:%[0-9]+]]:fr32 = ninf afn nofpexcept VMULSSrr killed [[VMULSSrr1]], killed [[VFMADD213SSr]], implicit $mxcsr
; CHECK-NEXT: [[VMULSSrr3:%[0-9]+]]:fr32 = ninf afn nofpexcept VMULSSrr [[COPY]], [[VMULSSrr2]], implicit $mxcsr
; CHECK-NEXT: [[VFMADD213SSr1:%[0-9]+]]:fr32 = ninf afn nofpexcept VFMADD213SSr [[VMULSSrr2]], [[VMULSSrr3]], [[VMOVSSrm_alt]], implicit $mxcsr
; CHECK-NEXT: [[VMULSSrr4:%[0-9]+]]:fr32 = ninf afn nofpexcept VMULSSrr [[VMULSSrr3]], [[VMOVSSrm_alt1]], implicit $mxcsr
; CHECK-NEXT: [[VMULSSrr5:%[0-9]+]]:fr32 = ninf afn nofpexcept VMULSSrr killed [[VMULSSrr4]], killed [[VFMADD213SSr1]], implicit $mxcsr
; CHECK-NEXT: [[VMULSSrr1:%[0-9]+]]:fr32 = ninf contract afn nofpexcept VMULSSrr [[VRSQRTSSr]], [[VMOVSSrm_alt1]], implicit $mxcsr
; CHECK-NEXT: [[VMULSSrr2:%[0-9]+]]:fr32 = ninf contract afn nofpexcept VMULSSrr killed [[VMULSSrr1]], killed [[VFMADD213SSr]], implicit $mxcsr
; CHECK-NEXT: [[VMULSSrr3:%[0-9]+]]:fr32 = ninf contract afn nofpexcept VMULSSrr [[COPY]], [[VMULSSrr2]], implicit $mxcsr
; CHECK-NEXT: [[VFMADD213SSr1:%[0-9]+]]:fr32 = ninf contract afn nofpexcept VFMADD213SSr [[VMULSSrr2]], [[VMULSSrr3]], [[VMOVSSrm_alt]], implicit $mxcsr
; CHECK-NEXT: [[VMULSSrr4:%[0-9]+]]:fr32 = ninf contract afn nofpexcept VMULSSrr [[VMULSSrr3]], [[VMOVSSrm_alt1]], implicit $mxcsr
; CHECK-NEXT: [[VMULSSrr5:%[0-9]+]]:fr32 = ninf contract afn nofpexcept VMULSSrr killed [[VMULSSrr4]], killed [[VFMADD213SSr1]], implicit $mxcsr
; CHECK-NEXT: [[COPY1:%[0-9]+]]:vr128 = COPY killed [[VMULSSrr5]]
; CHECK-NEXT: [[COPY2:%[0-9]+]]:vr128 = COPY [[COPY]]
; CHECK-NEXT: [[VPBROADCASTDrm:%[0-9]+]]:vr128 = VPBROADCASTDrm $rip, 1, $noreg, %const.2, $noreg :: (load (s32) from constant-pool)
Expand All @@ -46,7 +46,7 @@ define float @sqrt_ieee_ninf(float %f) #0 {
; CHECK-NEXT: [[COPY5:%[0-9]+]]:fr32 = COPY killed [[VPANDNrr]]
; CHECK-NEXT: $xmm0 = COPY [[COPY5]]
; CHECK-NEXT: RET 0, $xmm0
%call = tail call ninf afn float @llvm.sqrt.f32(float %f)
%call = tail call ninf afn contract float @llvm.sqrt.f32(float %f)
ret float %call
}

Expand All @@ -73,16 +73,18 @@ define float @sqrt_daz_ninf(float %f) #1 {
; CHECK-NEXT: [[DEF:%[0-9]+]]:fr32 = IMPLICIT_DEF
; CHECK-NEXT: [[VRSQRTSSr:%[0-9]+]]:fr32 = ninf afn VRSQRTSSr killed [[DEF]], [[COPY]]
; CHECK-NEXT: [[VMULSSrr:%[0-9]+]]:fr32 = ninf afn nofpexcept VMULSSrr [[COPY]], [[VRSQRTSSr]], implicit $mxcsr
; CHECK-NEXT: [[VMULSSrr1:%[0-9]+]]:fr32 = ninf afn nofpexcept VMULSSrr killed [[VMULSSrr]], [[VRSQRTSSr]], implicit $mxcsr
; CHECK-NEXT: [[VMOVSSrm_alt:%[0-9]+]]:fr32 = VMOVSSrm_alt $rip, 1, $noreg, %const.0, $noreg :: (load (s32) from constant-pool)
; CHECK-NEXT: [[VFMADD213SSr:%[0-9]+]]:fr32 = ninf afn nofpexcept VFMADD213SSr [[VRSQRTSSr]], killed [[VMULSSrr]], [[VMOVSSrm_alt]], implicit $mxcsr
; CHECK-NEXT: [[VADDSSrr:%[0-9]+]]:fr32 = ninf afn nofpexcept VADDSSrr killed [[VMULSSrr1]], [[VMOVSSrm_alt]], implicit $mxcsr
; CHECK-NEXT: [[VMOVSSrm_alt1:%[0-9]+]]:fr32 = VMOVSSrm_alt $rip, 1, $noreg, %const.1, $noreg :: (load (s32) from constant-pool)
; CHECK-NEXT: [[VMULSSrr1:%[0-9]+]]:fr32 = ninf afn nofpexcept VMULSSrr [[VRSQRTSSr]], [[VMOVSSrm_alt1]], implicit $mxcsr
; CHECK-NEXT: [[VMULSSrr2:%[0-9]+]]:fr32 = ninf afn nofpexcept VMULSSrr killed [[VMULSSrr1]], killed [[VFMADD213SSr]], implicit $mxcsr
; CHECK-NEXT: [[VMULSSrr3:%[0-9]+]]:fr32 = ninf afn nofpexcept VMULSSrr [[COPY]], [[VMULSSrr2]], implicit $mxcsr
; CHECK-NEXT: [[VFMADD213SSr1:%[0-9]+]]:fr32 = ninf afn nofpexcept VFMADD213SSr [[VMULSSrr2]], [[VMULSSrr3]], [[VMOVSSrm_alt]], implicit $mxcsr
; CHECK-NEXT: [[VMULSSrr4:%[0-9]+]]:fr32 = ninf afn nofpexcept VMULSSrr [[VMULSSrr3]], [[VMOVSSrm_alt1]], implicit $mxcsr
; CHECK-NEXT: [[VMULSSrr5:%[0-9]+]]:fr32 = ninf afn nofpexcept VMULSSrr killed [[VMULSSrr4]], killed [[VFMADD213SSr1]], implicit $mxcsr
; CHECK-NEXT: [[COPY1:%[0-9]+]]:vr128 = COPY killed [[VMULSSrr5]]
; CHECK-NEXT: [[VMULSSrr2:%[0-9]+]]:fr32 = ninf afn nofpexcept VMULSSrr [[VRSQRTSSr]], [[VMOVSSrm_alt1]], implicit $mxcsr
; CHECK-NEXT: [[VMULSSrr3:%[0-9]+]]:fr32 = ninf afn nofpexcept VMULSSrr killed [[VMULSSrr2]], killed [[VADDSSrr]], implicit $mxcsr
; CHECK-NEXT: [[VMULSSrr4:%[0-9]+]]:fr32 = ninf afn nofpexcept VMULSSrr [[COPY]], [[VMULSSrr3]], implicit $mxcsr
; CHECK-NEXT: [[VMULSSrr5:%[0-9]+]]:fr32 = ninf afn nofpexcept VMULSSrr [[VMULSSrr4]], [[VMULSSrr3]], implicit $mxcsr
; CHECK-NEXT: [[VADDSSrr1:%[0-9]+]]:fr32 = ninf afn nofpexcept VADDSSrr killed [[VMULSSrr5]], [[VMOVSSrm_alt]], implicit $mxcsr
; CHECK-NEXT: [[VMULSSrr6:%[0-9]+]]:fr32 = ninf afn nofpexcept VMULSSrr [[VMULSSrr4]], [[VMOVSSrm_alt1]], implicit $mxcsr
; CHECK-NEXT: [[VMULSSrr7:%[0-9]+]]:fr32 = ninf afn nofpexcept VMULSSrr killed [[VMULSSrr6]], killed [[VADDSSrr1]], implicit $mxcsr
; CHECK-NEXT: [[COPY1:%[0-9]+]]:vr128 = COPY killed [[VMULSSrr7]]
; CHECK-NEXT: [[FsFLD0SS:%[0-9]+]]:fr32 = FsFLD0SS
; CHECK-NEXT: [[VCMPSSrri:%[0-9]+]]:fr32 = nofpexcept VCMPSSrri [[COPY]], killed [[FsFLD0SS]], 0, implicit $mxcsr
; CHECK-NEXT: [[COPY2:%[0-9]+]]:vr128 = COPY killed [[VCMPSSrri]]
Expand Down
6 changes: 6 additions & 0 deletions llvm/tools/llc/llc.cpp
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Expand Up @@ -604,6 +604,12 @@ static int compileModule(char **argv, LLVMContext &Context,
InputFilename);
}

if (TheTriple.isX86() &&
codegen::getFuseFPOps() != FPOpFusion::FPOpFusionMode::Standard)
WithColor::warning(errs(), argv[0])
<< "X86 backend ignores --fp-contract setting; use IR fast-math "
"flags instead.";

Options.BinutilsVersion =
TargetMachine::parseBinutilsVersion(BinutilsVersion);
Options.MCOptions.ShowMCEncoding = ShowMCEncoding;
Expand Down
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