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[InstCombine] Fold fcmp ord/uno (fptrunc X), C to fcmp ord/uno X, C #185848

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[InstCombine] Fold fcmp ord/uno (fptrunc X), C to fcmp ord/uno X, C #185848

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a30fd37
Pre-commit tests
wermos Mar 11, 2026
0b45b75
Fold fcmp ord/uno (fptrunc X), C to fcmp ord/uno X, C.
wermos Mar 11, 2026
8720d1f
Update another test.
wermos Mar 11, 2026
0b282d9
Fix comment formatting.
wermos Mar 11, 2026
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52 changes: 30 additions & 22 deletions llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -8359,26 +8359,15 @@ static Instruction *foldFCmpReciprocalAndZero(FCmpInst &I, Instruction *LHSI,

// Transform 'fptrunc(x) cmp C' to 'x cmp ext(C)' if possible.
// Patterns include:
// fptrunc(x) < C --> x < ext(C)
// fptrunc(x) <= C --> x <= ext(C)
// fptrunc(x) > C --> x > ext(C)
// fptrunc(x) >= C --> x >= ext(C)
// fptrunc(x) < C --> x < ext(C)
// fptrunc(x) <= C --> x <= ext(C)
// fptrunc(x) > C --> x > ext(C)
// fptrunc(x) >= C --> x >= ext(C)
// fptrunc(x) ord/uno C --> x ord/uno C
// where 'ext(C)' is the extension of 'C' to the type of 'x' with a small bias
// due to precision loss.
static Instruction *foldFCmpFpTrunc(FCmpInst &I, const Instruction &FPTrunc,
const Constant &C) {
FCmpInst::Predicate Pred = I.getPredicate();
bool RoundDown = false;

if (Pred == FCmpInst::FCMP_OGE || Pred == FCmpInst::FCMP_UGE ||
Pred == FCmpInst::FCMP_OLT || Pred == FCmpInst::FCMP_ULT)
RoundDown = true;
else if (Pred == FCmpInst::FCMP_OGT || Pred == FCmpInst::FCMP_UGT ||
Pred == FCmpInst::FCMP_OLE || Pred == FCmpInst::FCMP_ULE)
RoundDown = false;
else
return nullptr;

const APFloat *CValue;
if (!match(&C, m_APFloat(CValue)))
return nullptr;
Expand All @@ -8393,19 +8382,38 @@ static Instruction *foldFCmpFpTrunc(FCmpInst &I, const Instruction &FPTrunc,
return Dest;
};

Type *DestType = FPTrunc.getOperand(0)->getType();
const fltSemantics &DestFltSema =
DestType->getScalarType()->getFltSemantics();

APFloat ExtCValue = ConvertFltSema(*CValue, DestFltSema);

FCmpInst::Predicate Pred = I.getPredicate();

// Fold fcmp ord/uno fptrunc X, C -> fcmp ord/uno X, C
if (Pred == FCmpInst::FCMP_ORD || Pred == FCmpInst::FCMP_UNO) {
return new FCmpInst(Pred, FPTrunc.getOperand(0),
ConstantFP::get(DestType, ExtCValue), "", &I);
}

bool RoundDown = false;

if (Pred == FCmpInst::FCMP_OGE || Pred == FCmpInst::FCMP_UGE ||
Pred == FCmpInst::FCMP_OLT || Pred == FCmpInst::FCMP_ULT)
RoundDown = true;
else if (Pred == FCmpInst::FCMP_OGT || Pred == FCmpInst::FCMP_UGT ||
Pred == FCmpInst::FCMP_OLE || Pred == FCmpInst::FCMP_ULE)
RoundDown = false;
else
return nullptr;

auto NextValue = [](const APFloat &Value, bool RoundDown) {
APFloat NextValue = Value;
NextValue.next(RoundDown);
return NextValue;
};

APFloat NextCValue = NextValue(*CValue, RoundDown);

Type *DestType = FPTrunc.getOperand(0)->getType();
const fltSemantics &DestFltSema =
DestType->getScalarType()->getFltSemantics();

APFloat ExtCValue = ConvertFltSema(*CValue, DestFltSema);
APFloat ExtNextCValue = ConvertFltSema(NextCValue, DestFltSema);

// When 'NextCValue' is infinity, use an imaged 'NextCValue' that equals
Expand Down
48 changes: 45 additions & 3 deletions llvm/test/Transforms/InstCombine/fold-fcmp-trunc.ll
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Expand Up @@ -104,7 +104,7 @@ define i1 @fcmp_trunc_with_reassoc(double %0) {
define i1 @fcmp_trunc_with_fast(double %0) {
; CHECK-LABEL: define i1 @fcmp_trunc_with_fast(
; CHECK-SAME: double [[TMP0:%.*]]) {
; CHECK-NEXT: [[RESULT:%.*]] = fcmp fast oge double [[TMP0]], 0x4058FFFFF0000000
; CHECK-NEXT: [[RESULT:%.*]] = fcmp fast oge double [[TMP0]], 0x4058FFFFF0000000
; CHECK-NEXT: ret i1 [[RESULT]]
;
%trunc = fptrunc double %0 to float
Expand Down Expand Up @@ -327,8 +327,7 @@ define i1 @fcmp_trunc_literal_positive_inf(double %0) {
define i1 @fcmp_trunc_literal_negative_inf(double %0) {
; CHECK-LABEL: define i1 @fcmp_trunc_literal_negative_inf(
; CHECK-SAME: double [[TMP0:%.*]]) {
; CHECK-NEXT: [[TRUNC:%.*]] = fptrunc double [[TMP0]] to float
; CHECK-NEXT: [[RESULT:%.*]] = fcmp uno float [[TRUNC]], 0.000000e+00
; CHECK-NEXT: [[RESULT:%.*]] = fcmp uno double [[TMP0]], 0.000000e+00
; CHECK-NEXT: ret i1 [[RESULT]]
;
%trunc = fptrunc double %0 to float
Expand Down Expand Up @@ -672,3 +671,46 @@ define i1 @fcmp_trunc_mn_ppc_fp128(ppc_fp128 %0) {
ret i1 %result
}

define i1 @fptrunc_uno_fcmp(double %arg0) {
; CHECK-LABEL: define i1 @fptrunc_uno_fcmp(
; CHECK-SAME: double [[ARG0:%.*]]) {
; CHECK-NEXT: [[V1:%.*]] = fcmp uno double [[ARG0]], 0.000000e+00
; CHECK-NEXT: ret i1 [[V1]]
;
%v0 = fptrunc double %arg0 to float
%v1 = fcmp uno float %v0, 0.000000e+00
ret i1 %v1
}

define i1 @fptrunc_uno_fcmp_commuted(double %arg0) {
; CHECK-LABEL: define i1 @fptrunc_uno_fcmp_commuted(
; CHECK-SAME: double [[ARG0:%.*]]) {
; CHECK-NEXT: [[V1:%.*]] = fcmp uno double [[ARG0]], 0.000000e+00
; CHECK-NEXT: ret i1 [[V1]]
;
%v0 = fptrunc double %arg0 to float
%v1 = fcmp uno float 7.000000e+00, %v0
ret i1 %v1
}

define i1 @fptrunc_ord_fcmp(double %arg0) {
; CHECK-LABEL: define i1 @fptrunc_ord_fcmp(
; CHECK-SAME: double [[ARG0:%.*]]) {
; CHECK-NEXT: [[V1:%.*]] = fcmp ord double [[ARG0]], 0.000000e+00
; CHECK-NEXT: ret i1 [[V1]]
;
%v0 = fptrunc double %arg0 to float
%v1 = fcmp ord float %v0, 0.000000e+00
ret i1 %v1
}

define i1 @fptrunc_ord_fcmp_commuted(double %arg0) {
; CHECK-LABEL: define i1 @fptrunc_ord_fcmp_commuted(
; CHECK-SAME: double [[ARG0:%.*]]) {
; CHECK-NEXT: [[V1:%.*]] = fcmp ord double [[ARG0]], 0.000000e+00
; CHECK-NEXT: ret i1 [[V1]]
;
%v0 = fptrunc double %arg0 to float
%v1 = fcmp ord float 7.000000e+00, %v0
ret i1 %v1
}
3 changes: 1 addition & 2 deletions llvm/test/Transforms/InstCombine/known-never-nan.ll
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Expand Up @@ -150,8 +150,7 @@ define i1 @fpext_maybe_nan(float %arg0) {

define i1 @fptrunc_maybe_nan(double %arg0) {
; CHECK-LABEL: @fptrunc_maybe_nan(
; CHECK-NEXT: [[OP:%.*]] = fptrunc double [[ARG0:%.*]] to float
; CHECK-NEXT: [[TMP:%.*]] = fcmp ord float [[OP]], 0.000000e+00
; CHECK-NEXT: [[TMP:%.*]] = fcmp ord double [[ARG0:%.*]], 0.000000e+00
; CHECK-NEXT: ret i1 [[TMP]]
;
%op = fptrunc double %arg0 to float
Expand Down