[InstCombine] Fold fpto{s|u}i non-norm to zero

Author: dtcxzyw

llvm/lib/Transforms/InstCombine/InstCombineCasts.cpp

@@ -1923,17 +1923,36 @@ Instruction *InstCombinerImpl::foldItoFPtoI(CastInst &FI) {
   return replaceInstUsesWith(FI, X);
 }
 
+static Instruction *foldFPtoI(Instruction &FI, InstCombiner &IC) {
+  // fpto{u/s}i non-norm --> 0
+  FPClassTest Mask =
+      FI.getOpcode() == Instruction::FPToUI ? fcPosNormal : fcNormal;
+  KnownFPClass FPClass =
+      computeKnownFPClass(FI.getOperand(0), Mask, /*Depth=*/0,
+                          IC.getSimplifyQuery().getWithInstruction(&FI));
+  if (FPClass.isKnownNever(Mask))
+    return IC.replaceInstUsesWith(FI, ConstantInt::getNullValue(FI.getType()));
+
+  return nullptr;
+}
+
 Instruction *InstCombinerImpl::visitFPToUI(FPToUIInst &FI) {
   if (Instruction *I = foldItoFPtoI(FI))
     return I;
 
+  if (Instruction *I = foldFPtoI(FI, *this))
+    return I;
+
   return commonCastTransforms(FI);
 }
 
 Instruction *InstCombinerImpl::visitFPToSI(FPToSIInst &FI) {
   if (Instruction *I = foldItoFPtoI(FI))
     return I;
 
+  if (Instruction *I = foldFPtoI(FI, *this))
+    return I;
+
   return commonCastTransforms(FI);
 }
 

llvm/test/Transforms/InstCombine/fpcast.ll

@@ -350,27 +350,23 @@ define double @masked_uint_to_fpext3(i32 %x) {
 
 define i32 @fptosi_nonnorm(float nofpclass(norm) %x) {
 ; CHECK-LABEL: @fptosi_nonnorm(
-; CHECK-NEXT:    [[RET:%.*]] = fptosi float [[X:%.*]] to i32
-; CHECK-NEXT:    ret i32 [[RET]]
+; CHECK-NEXT:    ret i32 0
 ;
   %ret = fptosi float %x to i32
   ret i32 %ret
 }
 
 define i32 @fptoui_nonnorm(float nofpclass(pnorm) %x) {
 ; CHECK-LABEL: @fptoui_nonnorm(
-; CHECK-NEXT:    [[RET:%.*]] = fptoui float [[X:%.*]] to i32
-; CHECK-NEXT:    ret i32 [[RET]]
+; CHECK-NEXT:    ret i32 0
 ;
   %ret = fptoui float %x to i32
   ret i32 %ret
 }
 
 define i32 @fptosi_nonnorm_copysign(float %x) {
 ; CHECK-LABEL: @fptosi_nonnorm_copysign(
-; CHECK-NEXT:    [[VAL:%.*]] = call float @llvm.copysign.f32(float 0.000000e+00, float [[X:%.*]])
-; CHECK-NEXT:    [[RET:%.*]] = fptosi float [[VAL]] to i32
-; CHECK-NEXT:    ret i32 [[RET]]
+; CHECK-NEXT:    ret i32 0
 ;
   %val = call float @llvm.copysign.f32(float 0.0, float %x)
   %ret = fptosi float %val to i32