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Fdim constant fold #109235

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Fdim constant fold #109235

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46f031f
[TLI] Add basic support for fdim libcall
braw-lee Sep 14, 2024
53989aa
[SimplifyLibCalls] Constant fold `fdim`
braw-lee Sep 15, 2024
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15 changes: 15 additions & 0 deletions llvm/include/llvm/Analysis/TargetLibraryInfo.def
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Expand Up @@ -2067,6 +2067,21 @@ TLI_DEFINE_ENUM_INTERNAL(remquol)
TLI_DEFINE_STRING_INTERNAL("remquol")
TLI_DEFINE_SIG_INTERNAL(LDbl, LDbl, LDbl, Ptr)

/// double fdim(double x, double y);
TLI_DEFINE_ENUM_INTERNAL(fdim)
TLI_DEFINE_STRING_INTERNAL("fdim")
TLI_DEFINE_SIG_INTERNAL(Dbl, Dbl, Dbl)

/// float fdimf(float x, float y);
TLI_DEFINE_ENUM_INTERNAL(fdimf)
TLI_DEFINE_STRING_INTERNAL("fdimf")
TLI_DEFINE_SIG_INTERNAL(Flt, Flt, Flt)

/// long double fdiml(long double x, long double y);
TLI_DEFINE_ENUM_INTERNAL(fdiml)
TLI_DEFINE_STRING_INTERNAL("fdiml")
TLI_DEFINE_SIG_INTERNAL(LDbl, LDbl, LDbl)

/// int remove(const char *path);
TLI_DEFINE_ENUM_INTERNAL(remove)
TLI_DEFINE_STRING_INTERNAL("remove")
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1 change: 1 addition & 0 deletions llvm/include/llvm/Transforms/Utils/SimplifyLibCalls.h
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Expand Up @@ -211,6 +211,7 @@ class LibCallSimplifier {
Value *optimizeTrigInversionPairs(CallInst *CI, IRBuilderBase &B);
Value *optimizeSymmetric(CallInst *CI, LibFunc Func, IRBuilderBase &B);
Value *optimizeRemquo(CallInst *CI, IRBuilderBase &B);
Value *optimizeFdim(CallInst *CI, IRBuilderBase &B);
// Wrapper for all floating point library call optimizations
Value *optimizeFloatingPointLibCall(CallInst *CI, LibFunc Func,
IRBuilderBase &B);
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2 changes: 2 additions & 0 deletions llvm/lib/Analysis/TargetLibraryInfo.cpp
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Expand Up @@ -306,6 +306,7 @@ static void initializeLibCalls(TargetLibraryInfoImpl &TLI, const Triple &T,
TLI.setUnavailable(LibFunc_powf);
TLI.setUnavailable(LibFunc_remainderf);
TLI.setUnavailable(LibFunc_remquof);
TLI.setUnavailable(LibFunc_fdimf);
TLI.setUnavailable(LibFunc_sinf);
TLI.setUnavailable(LibFunc_sinhf);
TLI.setUnavailable(LibFunc_sqrtf);
Expand Down Expand Up @@ -337,6 +338,7 @@ static void initializeLibCalls(TargetLibraryInfoImpl &TLI, const Triple &T,
TLI.setUnavailable(LibFunc_powl);
TLI.setUnavailable(LibFunc_remainderl);
TLI.setUnavailable(LibFunc_remquol);
TLI.setUnavailable(LibFunc_fdiml);
TLI.setUnavailable(LibFunc_sinl);
TLI.setUnavailable(LibFunc_sinhl);
TLI.setUnavailable(LibFunc_sqrtl);
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3 changes: 3 additions & 0 deletions llvm/lib/Transforms/Utils/BuildLibCalls.cpp
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Expand Up @@ -1191,6 +1191,9 @@ bool llvm::inferNonMandatoryLibFuncAttrs(Function &F,
case LibFunc_fabs:
case LibFunc_fabsf:
case LibFunc_fabsl:
case LibFunc_fdim:
case LibFunc_fdiml:
case LibFunc_fdimf:
case LibFunc_ffs:
case LibFunc_ffsl:
case LibFunc_ffsll:
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39 changes: 39 additions & 0 deletions llvm/lib/Transforms/Utils/SimplifyLibCalls.cpp
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Expand Up @@ -3080,6 +3080,41 @@ Value *LibCallSimplifier::optimizeRemquo(CallInst *CI, IRBuilderBase &B) {
return ConstantFP::get(CI->getType(), Rem);
}

/// Constant folds fdim
Value *LibCallSimplifier::optimizeFdim(CallInst *CI, IRBuilderBase &B) {
const APFloat *X, *Y;
// Check if both values are constants
if (!match(CI->getArgOperand(0), m_APFloat(X)) ||
!match(CI->getArgOperand(1), m_APFloat(Y)))
return nullptr;
// If either argument is NaN, NaN is returned
if (X->isNaN() || Y->isNaN())
return ConstantFP::getQNaN(CI->getType());

// If the difference if negative, return +0.0
if (*X <= *Y)
return ConstantFP::get(CI->getType(), 0.0);

APFloat ReturnVal = *X;
APFloat::opStatus Status =
ReturnVal.subtract(*Y, RoundingMode::NearestTiesToEven);
switch (Status) {
case APFloat::opStatus::opOK:
break;
case APFloat::opStatus::opOverflow:
return ConstantFP::get(
CI->getType(),
APFloat::getLargest(X->getSemantics(), /*Negative=*/false));
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The result should be inf. Please add a tests for fdim(1e308, -1e308).

BTW, it would be better to use fmax(x - y, 0) instead of handling all corner cases yourself.

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yes, I read that on cppref but wasn't sure if it will handle all corner cases,
will change to that

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The special cases also set errno, in which case we cannot perform the fold unless the call is memory(none)

case APFloat::opStatus::opUnderflow:
return ConstantFP::get(
CI->getType(),
APFloat::getLargest(X->getSemantics(), /*Negative=*/true));
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It is incorrect. Underflow means the result is subnormal.

default:
return nullptr;
}
return ConstantFP::get(CI->getType(), ReturnVal);
}

//===----------------------------------------------------------------------===//
// Integer Library Call Optimizations
//===----------------------------------------------------------------------===//
Expand Down Expand Up @@ -4009,6 +4044,10 @@ Value *LibCallSimplifier::optimizeFloatingPointLibCall(CallInst *CI,
if (hasFloatVersion(M, CI->getCalledFunction()->getName()))
return optimizeBinaryDoubleFP(CI, Builder, TLI);
return nullptr;
case LibFunc_fdim:
case LibFunc_fdimf:
case LibFunc_fdiml:
return optimizeFdim(CI, Builder);
case LibFunc_fminf:
case LibFunc_fmin:
case LibFunc_fminl:
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10 changes: 10 additions & 0 deletions llvm/test/Transforms/InferFunctionAttrs/annotate.ll
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Expand Up @@ -830,6 +830,16 @@ declare float @remquof(float, float, ptr)
; CHECK: declare x86_fp80 @remquol(x86_fp80, x86_fp80, ptr nocapture) [[NOFREE_NOUNWIND_WILLRETURN_WRITEONLY]]
declare x86_fp80 @remquol(x86_fp80, x86_fp80, ptr)


; CHECK: declare double @fdim(double, double) [[NOFREE_NOUNWIND_WILLRETURN_WRITEONLY]]
declare double @fdim(double, double)

; CHECK: declare float @fdimf(float, float) [[NOFREE_NOUNWIND_WILLRETURN_WRITEONLY]]
declare float @fdimf(float, float)

; CHECK: declare x86_fp80 @fdiml(x86_fp80, x86_fp80) [[NOFREE_NOUNWIND_WILLRETURN_WRITEONLY]]
declare x86_fp80 @fdiml(x86_fp80, x86_fp80)

; CHECK: declare noundef i32 @rename(ptr nocapture noundef readonly, ptr nocapture noundef readonly) [[NOFREE_NOUNWIND]]
declare i32 @rename(ptr, ptr)

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37 changes: 37 additions & 0 deletions llvm/test/Transforms/InstCombine/fdim.ll
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@@ -0,0 +1,37 @@
; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 5
; RUN: opt < %s -passes=instcombine -S | FileCheck %s

define double @fdim_double() {
; CHECK-LABEL: define double @fdim_double() {
; CHECK-NEXT: ret double 2.500000e+00
;
%dim = call double @fdim (double 10.5, double 8.0)
ret double %dim
}

define double @fdim_double1() {
; CHECK-LABEL: define double @fdim_double1() {
; CHECK-NEXT: ret double 0.000000e+00
;
%dim = call double @fdim (double 7.0, double 8.0)
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Extra space before ( in all functions

ret double %dim
}

define float @fdim_float() {
; CHECK-LABEL: define float @fdim_float() {
; CHECK-NEXT: ret float 2.500000e+00
;
%dim = call float @fdimf (float 10.5, float 8.0)
ret float %dim
}

define float @fdim_float1() {
; CHECK-LABEL: define float @fdim_float1() {
; CHECK-NEXT: ret float 0.000000e+00
;
%dim = call float @fdimf (float 7.0, float 8.0)
ret float %dim
}

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Needs tests for all the edge cases. Can you also test poison/undef arguments in each position

declare double @fdim(double, double)
declare float @fdimf(float, float)
20 changes: 16 additions & 4 deletions llvm/test/tools/llvm-tli-checker/ps4-tli-check.yaml
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Expand Up @@ -34,7 +34,7 @@
#
# CHECK: << Total TLI yes SDK no: 18
# CHECK: >> Total TLI no SDK yes: 0
# CHECK: == Total TLI yes SDK yes: 250
# CHECK: == Total TLI yes SDK yes: 253
#
# WRONG_DETAIL: << TLI yes SDK no : '_ZdaPv' aka operator delete[](void*)
# WRONG_DETAIL: >> TLI no SDK yes: '_ZdaPvj' aka operator delete[](void*, unsigned int)
Expand All @@ -48,14 +48,14 @@
# WRONG_DETAIL: << TLI yes SDK no : 'fminimum_numl'
# WRONG_SUMMARY: << Total TLI yes SDK no: 19{{$}}
# WRONG_SUMMARY: >> Total TLI no SDK yes: 1{{$}}
# WRONG_SUMMARY: == Total TLI yes SDK yes: 249
# WRONG_SUMMARY: == Total TLI yes SDK yes: 252
#
## The -COUNT suffix doesn't care if there are too many matches, so check
## the exact count first; the two directives should add up to that.
## Yes, this means additions to TLI will fail this test, but the argument
## to -COUNT can't be an expression.
# AVAIL: TLI knows 501 symbols, 268 available
# AVAIL-COUNT-268: {{^}} available
# AVAIL: TLI knows 504 symbols, 271 available
# AVAIL-COUNT-271: {{^}} available
# AVAIL-NOT: {{^}} available
# UNAVAIL-COUNT-233: not available
# UNAVAIL-NOT: not available
Expand Down Expand Up @@ -814,6 +814,18 @@ DynamicSymbols:
Type: STT_FUNC
Section: .text
Binding: STB_GLOBAL
- Name: fdim
Type: STT_FUNC
Section: .text
Binding: STB_GLOBAL
- Name: fdimf
Type: STT_FUNC
Section: .text
Binding: STB_GLOBAL
- Name: fdiml
Type: STT_FUNC
Section: .text
Binding: STB_GLOBAL
- Name: rewind
Type: STT_FUNC
Section: .text
Expand Down
3 changes: 3 additions & 0 deletions llvm/unittests/Analysis/TargetLibraryInfoTest.cpp
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Expand Up @@ -317,6 +317,9 @@ TEST_F(TargetLibraryInfoTest, ValidProto) {
"declare double @remquo(double, double, ptr)\n"
"declare float @remquof(float, float, ptr)\n"
"declare x86_fp80 @remquol(x86_fp80, x86_fp80, ptr)\n"
"declare double @fdim(double, double)\n"
"declare float @fdimf(float, float)\n"
"declare x86_fp80 @fdiml(x86_fp80, x86_fp80)\n"
"declare i32 @rename(i8*, i8*)\n"
"declare void @rewind(%struct*)\n"
"declare double @rint(double)\n"
Expand Down
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