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[InstCombine] Fold fptrunc(x) ord/uno [ C | fptrunc(y) ] to x ord/uno [ C | y ] #185844

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Merged
Camsyn merged 7 commits into from
Apr 15, 2026
Merged

[InstCombine] Fold fptrunc(x) ord/uno [ C | fptrunc(y) ] to x ord/uno [ C | y ] #185844

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0c191e8
Before-commit test
Camsyn Mar 11, 2026
b4dd5f5
Fix #185698
Camsyn Mar 11, 2026
a75e8c7
After-commit test
Camsyn Mar 11, 2026
1ec82b7
Follow the review comments
Camsyn Apr 13, 2026
2efbf30
Adjust comments
Camsyn Apr 13, 2026
15ed883
Fix incorrect pattern
Camsyn Apr 14, 2026
8752638
Fix: trunc -> fptrunc
Camsyn Apr 14, 2026
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37 changes: 28 additions & 9 deletions llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -26,6 +26,7 @@
#include "llvm/IR/Constants.h"
#include "llvm/IR/DataLayout.h"
#include "llvm/IR/InstrTypes.h"
#include "llvm/IR/Instruction.h"
#include "llvm/IR/Instructions.h"
#include "llvm/IR/IntrinsicInst.h"
#include "llvm/IR/PatternMatch.h"
Expand Down Expand Up @@ -8290,15 +8291,32 @@ 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 0
// 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();
Type *DestType = FPTrunc.getOperand(0)->getType();

const APFloat *CValue;
// TODO: support vec
if (!match(&C, m_APFloat(CValue)))
return nullptr;

// Handle ord/uno
if (Pred == FCmpInst::FCMP_ORD || Pred == FCmpInst::FCMP_UNO) {
assert(!CValue->isNaN() &&
"X ord/uno NaN should be folded away by simplifyFCmpInst()");
return new FCmpInst(Pred, FPTrunc.getOperand(0),
ConstantFP::getZero(DestType), "", &I);
}

// Handle <, >, <=, >=
bool RoundDown = false;

if (Pred == FCmpInst::FCMP_OGE || Pred == FCmpInst::FCMP_UGE ||
Expand All @@ -8310,10 +8328,6 @@ static Instruction *foldFCmpFpTrunc(FCmpInst &I, const Instruction &FPTrunc,
else
return nullptr;

const APFloat *CValue;
if (!match(&C, m_APFloat(CValue)))
return nullptr;

if (CValue->isNaN() || CValue->isInfinity())
return nullptr;

Expand All @@ -8332,7 +8346,6 @@ static Instruction *foldFCmpFpTrunc(FCmpInst &I, const Instruction &FPTrunc,

APFloat NextCValue = NextValue(*CValue, RoundDown);

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

Expand Down Expand Up @@ -8904,6 +8917,12 @@ Instruction *InstCombinerImpl::visitFCmpInst(FCmpInst &I) {
if (match(Op1, m_FAdd(m_Value(Y), m_AnyZeroFP())))
return new FCmpInst(Pred, Op0, Y, "", &I);

// fcmp ord/uno (fptrunc X), (fptrunc Y) -> fcmp ord/uno X, Y
if ((Pred == FCmpInst::FCMP_ORD || Pred == FCmpInst::FCMP_UNO) &&
match(Op0, m_FPTrunc(m_Value(X))) && match(Op1, m_FPTrunc(m_Value(Y))) &&
X->getType() == Y->getType())
return new FCmpInst(Pred, X, Y, "", &I);

if (match(Op0, m_FPExt(m_Value(X)))) {
// fcmp (fpext X), (fpext Y) -> fcmp X, Y
if (match(Op1, m_FPExt(m_Value(Y))) && X->getType() == Y->getType())
Expand Down
51 changes: 48 additions & 3 deletions llvm/test/Transforms/InstCombine/fold-fcmp-trunc.ll
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Expand Up @@ -57,6 +57,52 @@ define i1 @fcmp_trunc_zero(double %0) {
ret i1 %result
}

define i1 @fcmp_trunc_uno(double %0) {
; CHECK-LABEL: define i1 @fcmp_trunc_uno(
; CHECK-SAME: double [[TMP0:%.*]]) {
; CHECK-NEXT: [[RESULT:%.*]] = fcmp uno double [[TMP0]], 0.000000e+00
; CHECK-NEXT: ret i1 [[RESULT]]
;
%trunc = fptrunc double %0 to float
%result = fcmp uno float %trunc, 0.000000e+00
ret i1 %result
}

define i1 @fcmp_trunc_ord_inf(double %0) {
; CHECK-LABEL: define i1 @fcmp_trunc_ord_inf(
; CHECK-SAME: double [[TMP0:%.*]]) {
; CHECK-NEXT: [[RESULT:%.*]] = fcmp ord double [[TMP0]], 0.000000e+00
; CHECK-NEXT: ret i1 [[RESULT]]
;
%trunc = fptrunc double %0 to float
%result = fcmp ord float %trunc, 0x7FF0000000000000
ret i1 %result
}

define i1 @fcmp_trunc_pair_uno(double %x, double %y) {
; CHECK-LABEL: define i1 @fcmp_trunc_pair_uno(
; CHECK-SAME: double [[X:%.*]], double [[Y:%.*]]) {
; CHECK-NEXT: [[RESULT:%.*]] = fcmp uno double [[X]], [[Y]]
; CHECK-NEXT: ret i1 [[RESULT]]
;
%tx = fptrunc double %x to float
%ty = fptrunc double %y to float
%result = fcmp uno float %tx, %ty
ret i1 %result
}

define i1 @fcmp_trunc_pair_ord(double %x, double %y) {
; CHECK-LABEL: define i1 @fcmp_trunc_pair_ord(
; CHECK-SAME: double [[X:%.*]], double [[Y:%.*]]) {
; CHECK-NEXT: [[RESULT:%.*]] = fcmp ord double [[X]], [[Y]]
; CHECK-NEXT: ret i1 [[RESULT]]
;
%tx = fptrunc double %x to float
%ty = fptrunc double %y to float
%result = fcmp ord float %tx, %ty
ret i1 %result
}

define i1 @fcmp_trunc_with_nnan(double %0) {
; CHECK-LABEL: define i1 @fcmp_trunc_with_nnan(
; CHECK-SAME: double [[TMP0:%.*]]) {
Expand Down Expand Up @@ -104,7 +150,7 @@ 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 +373,7 @@ 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
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