[InstCombine] Handle FMF in SimplifyDemandedUseFPClass

Author: dtcxzyw

llvm/lib/Transforms/InstCombine/InstCombineSimplifyDemanded.cpp

@@ -1959,9 +1959,11 @@ static Constant *getFPClassConstant(Type *Ty, FPClassTest Mask) {
   }
 }
 
-Value *InstCombinerImpl::SimplifyDemandedUseFPClass(
-    Value *V, const FPClassTest DemandedMask, KnownFPClass &Known,
-    unsigned Depth, Instruction *CxtI) {
+Value *InstCombinerImpl::SimplifyDemandedUseFPClass(Value *V,
+                                                    FPClassTest DemandedMask,
+                                                    KnownFPClass &Known,
+                                                    unsigned Depth,
+                                                    Instruction *CxtI) {
   assert(Depth <= MaxAnalysisRecursionDepth && "Limit Search Depth");
   Type *VTy = V->getType();
 
@@ -1985,7 +1987,12 @@ Value *InstCombinerImpl::SimplifyDemandedUseFPClass(
   if (!I->hasOneUse())
     return nullptr;
 
-  // TODO: Should account for nofpclass/FastMathFlags on current instruction
+  if (auto *FPOp = dyn_cast<FPMathOperator>(I)) {
+    if (FPOp->hasNoNaNs())
+      DemandedMask &= ~fcNan;
+    if (FPOp->hasNoInfs())
+      DemandedMask &= ~fcInf;
+  }
   switch (I->getOpcode()) {
   case Instruction::FNeg: {
     if (SimplifyDemandedFPClass(I, 0, llvm::fneg(DemandedMask), Known,

llvm/test/Transforms/InstCombine/simplify-demanded-fpclass.ll

@@ -693,7 +693,8 @@ define nofpclass(pinf pnorm psub pzero) float @ret_nofpclass_nopositives_copysig
 define nofpclass(pinf pnorm psub pzero) float @ret_nofpclass_nopositives_copysign_nnan_flag(float %x, float %unknown.sign) {
 ; CHECK-LABEL: define nofpclass(pinf pzero psub pnorm) float @ret_nofpclass_nopositives_copysign_nnan_flag
 ; CHECK-SAME: (float [[X:%.*]], float [[UNKNOWN_SIGN:%.*]]) {
-; CHECK-NEXT:    [[COPYSIGN:%.*]] = call nnan float @llvm.copysign.f32(float [[X]], float [[UNKNOWN_SIGN]])
+; CHECK-NEXT:    [[TMP1:%.*]] = call nnan float @llvm.fabs.f32(float [[X]])
+; CHECK-NEXT:    [[COPYSIGN:%.*]] = fneg nnan float [[TMP1]]
 ; CHECK-NEXT:    ret float [[COPYSIGN]]
 ;
   %copysign = call nnan float @llvm.copysign.f32(float %x, float %unknown.sign)
@@ -727,7 +728,7 @@ define nofpclass(ninf nnorm nsub nzero) float @ret_nofpclass_nonegatives_copysig
 define nofpclass(ninf nnorm nsub nzero) float @ret_nofpclass_nonegatives_copysign_nnan_flag(float %x, float %unknown.sign) {
 ; CHECK-LABEL: define nofpclass(ninf nzero nsub nnorm) float @ret_nofpclass_nonegatives_copysign_nnan_flag
 ; CHECK-SAME: (float [[X:%.*]], float [[UNKNOWN_SIGN:%.*]]) {
-; CHECK-NEXT:    [[COPYSIGN:%.*]] = call nnan float @llvm.copysign.f32(float [[X]], float [[UNKNOWN_SIGN]])
+; CHECK-NEXT:    [[COPYSIGN:%.*]] = call nnan float @llvm.fabs.f32(float [[X]])
 ; CHECK-NEXT:    ret float [[COPYSIGN]]
 ;
   %copysign = call nnan float @llvm.copysign.f32(float %x, float %unknown.sign)