[InstCombine] Drop ninf when folding fptrunc(fabs(X)) -> fabs()fpfptrunc X)

Author: dtcxzyw

llvm/lib/Transforms/InstCombine/InstCombineCasts.cpp

@@ -1918,6 +1918,9 @@ Instruction *InstCombinerImpl::visitFPTrunc(FPTruncInst &FPT) {
       CallInst *NewCI =
           CallInst::Create(Overload, {InnerTrunc}, OpBundles, II->getName());
       NewCI->copyFastMathFlags(II);
+      // A normal value may be converted to an infinity.
+      if (II->getIntrinsicID() == Intrinsic::fabs)
+        NewCI->setHasNoInfs(FPT.hasNoInfs());
       return NewCI;
     }
     }

llvm/test/Transforms/InstCombine/fpcast.ll

@@ -32,7 +32,7 @@ define half @test3(float %a) {
 define half @test3_fast(float %a) {
 ; CHECK-LABEL: @test3_fast(
 ; CHECK-NEXT:    [[TMP1:%.*]] = fptrunc float [[A:%.*]] to half
-; CHECK-NEXT:    [[C:%.*]] = call half @llvm.fabs.f16(half [[TMP1]])
+; CHECK-NEXT:    [[C:%.*]] = call ninf half @llvm.fabs.f16(half [[TMP1]])
 ; CHECK-NEXT:    ret half [[C]]
 ;
   %b = call float @llvm.fabs.f32(float %a)
@@ -54,7 +54,7 @@ define half @test3_both_ninf(float %a) {
 define half @test3_fabs_ninf(float %a) {
 ; CHECK-LABEL: @test3_fabs_ninf(
 ; CHECK-NEXT:    [[TMP1:%.*]] = fptrunc float [[A:%.*]] to half
-; CHECK-NEXT:    [[C:%.*]] = call ninf half @llvm.fabs.f16(half [[TMP1]])
+; CHECK-NEXT:    [[C:%.*]] = call half @llvm.fabs.f16(half [[TMP1]])
 ; CHECK-NEXT:    ret half [[C]]
 ;
   %b = call ninf float @llvm.fabs.f32(float %a)