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[InstCombine] Fold fmod to frem if we know it does not set errno. (#107912)
fmod will be folded to frem in clang under -fno-math-errno and can be constant folded in llvm if the operands are known. It can be relatively common to have fp code that handles special values before doing some calculation: ``` if (isnan(f)) return handlenan; if (isinf(f)) return handleinf; .. fmod(f, 2.0) ``` This patch enables the folding of fmod to frem in instcombine if the first parameter is not inf and the second is not zero. Other combinations do not set errno. The same transform is performed for fmod with the nnan flag, which implies the input is known to not be inf/zero.
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‎llvm/include/llvm/Transforms/Utils/SimplifyLibCalls.h‎

Lines changed: 1 addition & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -206,6 +206,7 @@ class LibCallSimplifier {
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Value *optimizeFMinFMax(CallInst *CI, IRBuilderBase &B);
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Value *optimizeLog(CallInst *CI, IRBuilderBase &B);
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Value *optimizeSqrt(CallInst *CI, IRBuilderBase &B);
209+
Value *optimizeFMod(CallInst *CI, IRBuilderBase &B);
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Value *mergeSqrtToExp(CallInst *CI, IRBuilderBase &B);
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Value *optimizeSinCosPi(CallInst *CI, bool IsSin, IRBuilderBase &B);
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Value *optimizeTrigInversionPairs(CallInst *CI, IRBuilderBase &B);

‎llvm/lib/Transforms/Utils/SimplifyLibCalls.cpp‎

Lines changed: 33 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -2796,6 +2796,35 @@ Value *LibCallSimplifier::optimizeSqrt(CallInst *CI, IRBuilderBase &B) {
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return copyFlags(*CI, FabsCall);
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}
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2799+
Value *LibCallSimplifier::optimizeFMod(CallInst *CI, IRBuilderBase &B) {
2800+
SimplifyQuery SQ(DL, TLI, DT, AC, CI, true, true, DC);
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// fmod(x,y) can set errno if y == 0 or x == +/-inf, and returns Nan in those
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// case. If we know those do not happen, then we can convert the fmod into
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// frem.
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bool IsNoNan = CI->hasNoNaNs();
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if (!IsNoNan) {
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KnownFPClass Known0 = computeKnownFPClass(CI->getOperand(0), fcInf,
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/*Depth=*/0, SQ);
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if (Known0.isKnownNeverInfinity()) {
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KnownFPClass Known1 =
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computeKnownFPClass(CI->getOperand(1), fcZero | fcSubnormal,
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/*Depth=*/0, SQ);
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Function *F = CI->getParent()->getParent();
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if (Known1.isKnownNeverLogicalZero(*F, CI->getType()))
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IsNoNan = true;
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}
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}
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if (IsNoNan) {
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Value *FRem = B.CreateFRemFMF(CI->getOperand(0), CI->getOperand(1), CI);
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if (auto *FRemI = dyn_cast<Instruction>(FRem))
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FRemI->setHasNoNaNs(true);
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substituteInParent(CI, FRem);
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}
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return nullptr;
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}
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Value *LibCallSimplifier::optimizeTrigInversionPairs(CallInst *CI,
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IRBuilderBase &B) {
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Module *M = CI->getModule();
@@ -3945,6 +3974,10 @@ Value *LibCallSimplifier::optimizeFloatingPointLibCall(CallInst *CI,
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case LibFunc_sqrt:
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case LibFunc_sqrtl:
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return optimizeSqrt(CI, Builder);
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case LibFunc_fmod:
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case LibFunc_fmodf:
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case LibFunc_fmodl:
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return optimizeFMod(CI, Builder);
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case LibFunc_logf:
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case LibFunc_log:
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case LibFunc_logl:

‎llvm/test/Transforms/InstCombine/fmod.ll‎

Lines changed: 21 additions & 9 deletions
Original file line numberDiff line numberDiff line change
@@ -9,7 +9,7 @@ define float @test_inf_const(float %f) {
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; CHECK-NEXT: [[ISINF:%.*]] = fcmp oeq float [[ABS]], 0x7FF0000000000000
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; CHECK-NEXT: br i1 [[ISINF]], label [[RETURN:%.*]], label [[IF_END:%.*]]
1111
; CHECK: if.end:
12-
; CHECK-NEXT: [[CALL:%.*]] = tail call float @fmodf(float [[F]], float 2.000000e+00)
12+
; CHECK-NEXT: [[CALL:%.*]] = frem nnan float [[F]], 2.000000e+00
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; CHECK-NEXT: ret float [[CALL]]
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; CHECK: return:
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; CHECK-NEXT: ret float 0.000000e+00
@@ -34,7 +34,7 @@ define float @test_const_zero(float %f) {
3434
; CHECK-NEXT: [[ISZERO:%.*]] = fcmp oeq float [[F]], 0.000000e+00
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; CHECK-NEXT: br i1 [[ISZERO]], label [[RETURN:%.*]], label [[IF_END:%.*]]
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; CHECK: if.end:
37-
; CHECK-NEXT: [[CALL:%.*]] = tail call float @fmodf(float 2.000000e+00, float [[F]])
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; CHECK-NEXT: [[CALL:%.*]] = frem nnan float 2.000000e+00, [[F]]
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; CHECK-NEXT: ret float [[CALL]]
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; CHECK: return:
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; CHECK-NEXT: ret float 0.000000e+00
@@ -67,19 +67,19 @@ define float @test_noinf_nozero(float nofpclass(inf) %f, float nofpclass(zero) %
6767
; CHECK-LABEL: define float @test_noinf_nozero(
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; CHECK-SAME: float nofpclass(inf) [[F:%.*]], float nofpclass(zero) [[G:%.*]]) {
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; CHECK-NEXT: entry:
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; CHECK-NEXT: [[CALL:%.*]] = tail call nnan float @fmodf(float [[F]], float [[G]])
70+
; CHECK-NEXT: [[CALL:%.*]] = frem nnan float [[F]], [[G]]
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; CHECK-NEXT: ret float [[CALL]]
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;
7373
entry:
74-
%call = tail call nnan float @fmodf(float %f, float %g)
74+
%call = tail call float @fmodf(float %f, float %g)
7575
ret float %call
7676
}
7777

7878
define double @test_double(double nofpclass(inf) %f, double nofpclass(zero) %g) {
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; CHECK-LABEL: define double @test_double(
8080
; CHECK-SAME: double nofpclass(inf) [[F:%.*]], double nofpclass(zero) [[G:%.*]]) {
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; CHECK-NEXT: entry:
82-
; CHECK-NEXT: [[CALL:%.*]] = tail call double @fmod(double [[F]], double [[G]])
82+
; CHECK-NEXT: [[CALL:%.*]] = frem nnan double [[F]], [[G]]
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; CHECK-NEXT: ret double [[CALL]]
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;
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entry:
@@ -91,7 +91,7 @@ define fp128 @test_fp128(fp128 nofpclass(inf) %f, fp128 nofpclass(zero) %g) {
9191
; CHECK-LABEL: define fp128 @test_fp128(
9292
; CHECK-SAME: fp128 nofpclass(inf) [[F:%.*]], fp128 nofpclass(zero) [[G:%.*]]) {
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; CHECK-NEXT: entry:
94-
; CHECK-NEXT: [[CALL:%.*]] = tail call fp128 @fmodl(fp128 [[F]], fp128 [[G]])
94+
; CHECK-NEXT: [[CALL:%.*]] = frem nnan fp128 [[F]], [[G]]
9595
; CHECK-NEXT: ret fp128 [[CALL]]
9696
;
9797
entry:
@@ -103,19 +103,31 @@ define float @test_noinf_nozero_dazpreservesign(float nofpclass(inf) %f, float n
103103
; CHECK-LABEL: define float @test_noinf_nozero_dazpreservesign(
104104
; CHECK-SAME: float nofpclass(inf) [[F:%.*]], float nofpclass(zero) [[G:%.*]]) #[[ATTR0:[0-9]+]] {
105105
; CHECK-NEXT: entry:
106-
; CHECK-NEXT: [[CALL:%.*]] = tail call nnan float @fmodf(float [[F]], float [[G]])
106+
; CHECK-NEXT: [[CALL:%.*]] = tail call float @fmodf(float [[F]], float [[G]])
107107
; CHECK-NEXT: ret float [[CALL]]
108108
;
109109
entry:
110-
%call = tail call nnan float @fmodf(float %f, float %g)
110+
%call = tail call float @fmodf(float %f, float %g)
111111
ret float %call
112112
}
113113

114114
define float @test_noinf_nozero_dazdynamic(float nofpclass(inf) %f, float nofpclass(zero) %g) "denormal-fp-math"="dynamic,dynamic" {
115115
; CHECK-LABEL: define float @test_noinf_nozero_dazdynamic(
116116
; CHECK-SAME: float nofpclass(inf) [[F:%.*]], float nofpclass(zero) [[G:%.*]]) #[[ATTR1:[0-9]+]] {
117117
; CHECK-NEXT: entry:
118-
; CHECK-NEXT: [[CALL:%.*]] = tail call nnan float @fmodf(float [[F]], float [[G]])
118+
; CHECK-NEXT: [[CALL:%.*]] = tail call float @fmodf(float [[F]], float [[G]])
119+
; CHECK-NEXT: ret float [[CALL]]
120+
;
121+
entry:
122+
%call = tail call float @fmodf(float %f, float %g)
123+
ret float %call
124+
}
125+
126+
define float @test_nnan(float %f, float %g) {
127+
; CHECK-LABEL: define float @test_nnan(
128+
; CHECK-SAME: float [[F:%.*]], float [[G:%.*]]) {
129+
; CHECK-NEXT: entry:
130+
; CHECK-NEXT: [[CALL:%.*]] = frem nnan float [[F]], [[G]]
119131
; CHECK-NEXT: ret float [[CALL]]
120132
;
121133
entry:

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