[SimplifyLibCalls] Constant fold fdim

Signed-off-by: Kushal Pal <[email protected]>

Author: braw-lee

llvm/include/llvm/Transforms/Utils/SimplifyLibCalls.h

@@ -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);

llvm/lib/Transforms/Utils/SimplifyLibCalls.cpp

@@ -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));
+  case APFloat::opStatus::opUnderflow:
+    return ConstantFP::get(
+        CI->getType(),
+        APFloat::getLargest(X->getSemantics(), /*Negative=*/true));
+  default:
+    return nullptr;
+  }
+  return ConstantFP::get(CI->getType(), ReturnVal);
+}
+
 //===----------------------------------------------------------------------===//
 // Integer Library Call Optimizations
 //===----------------------------------------------------------------------===//
@@ -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:

llvm/test/Transforms/InstCombine/fdim.ll

@@ -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)
+  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
+}
+
+declare double @fdim(double, double)
+declare float @fdimf(float, float)