InstCombine: Fold out is_fpclass inf checks from test mask for known finite sources

[arsenm]

Summary

Make the partner transform already done for nnan sources.

[sepavloff]

LGTM

[arsenm]

Also handle negated case

[arsenm]

Don't bother with replaceOperand for the constant, it doesn't need to go to the worklist

[arsenm]

5ccbd07dd607bac8a05016d80e3fa34f2d393279

llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp

Instruction *InstCombinerImpl::foldIntrinsicIsFPClass(IntrinsicInst &II) {
   if ((Mask & fcNan) && isKnownNeverNaN(Src0, &getTargetLibraryInfo())) {
     return replaceOperand(II, 1,
                           ConstantInt::get(Src1->getType(), Mask & ~fcNan));
   }
 
   // TODO: Handle inverted mask cases, e.g.
   // fp_class (nnan x), ~(qnan|snan) -> true
 
+  // fp_class (ninf x), ninf|pinf|other -> fp_class (ninf x), other
+  if ((Mask & fcInf) && isKnownNeverInfinity(Src0, &getTargetLibraryInfo())) {
+    return replaceOperand(II, 1,
+                          ConstantInt::get(Src1->getType(), Mask & ~fcInf));
+  }
+
   // Clamp mask to used bits
   if ((Mask & fcAllFlags) != Mask) {
     CallInst *NewCall = Builder.CreateCall(
       II.getCalledFunction(),
       {Src0, ConstantInt::get(Src1->getType(), Mask & fcAllFlags)});
 
     NewCall->takeName(&II);
     return replaceInstUsesWith(II, NewCall);

llvm/test/Transforms/InstCombine/is_fpclass.ll

 }
 
 ; --------------------------------------------------------------------
 ; llvm.is.fpclass with ninf sources
 ; --------------------------------------------------------------------
 
 define i1 @test_class_is_ninf_pinf_ninf_src(float %x) {
 ; CHECK-LABEL: @test_class_is_ninf_pinf_ninf_src(
-; CHECK-NEXT:    [[NINF:%.*]] = fadd ninf float [[X:%.*]], 1.000000e+00
-; CHECK-NEXT:    [[CLASS:%.*]] = call i1 @llvm.is.fpclass.f32(float [[NINF]], i32 516)
-; CHECK-NEXT:    ret i1 [[CLASS]]
+; CHECK-NEXT:    ret i1 false
 ;
   %ninf = fadd ninf float %x, 1.0
   %class = call i1 @llvm.is.fpclass.f32(float %ninf, i32 516)
   ret i1 %class
 }
 
 define i1 @test_class_is_ninf_ninf_src(float %x) {
 ; CHECK-LABEL: @test_class_is_ninf_ninf_src(
-; CHECK-NEXT:    [[NINF:%.*]] = fadd ninf float [[X:%.*]], 1.000000e+00
-; CHECK-NEXT:    [[CLASS:%.*]] = call i1 @llvm.is.fpclass.f32(float [[NINF]], i32 4)
-; CHECK-NEXT:    ret i1 [[CLASS]]
+; CHECK-NEXT:    ret i1 false
 ;
   %ninf = fadd ninf float %x, 1.0
   %class = call i1 @llvm.is.fpclass.f32(float %ninf, i32 4)
   ret i1 %class
 }
 
 define i1 @test_class_is_pinf_ninf_src(float %x) {
 ; CHECK-LABEL: @test_class_is_pinf_ninf_src(
-; CHECK-NEXT:    [[NINF:%.*]] = fadd ninf float [[X:%.*]], 1.000000e+00
-; CHECK-NEXT:    [[CLASS:%.*]] = call i1 @llvm.is.fpclass.f32(float [[NINF]], i32 512)
-; CHECK-NEXT:    ret i1 [[CLASS]]
+; CHECK-NEXT:    ret i1 false
 ;
   %ninf = fadd ninf float %x, 1.0
   %class = call i1 @llvm.is.fpclass.f32(float %ninf, i32 512)
   ret i1 %class
 }
 
 define i1 @test_class_is_ninf_pinf_pnormal_ninf_src(float %x) {
 ; CHECK-LABEL: @test_class_is_ninf_pinf_pnormal_ninf_src(
 ; CHECK-NEXT:    [[NINF:%.*]] = fadd ninf float [[X:%.*]], 1.000000e+00
-; CHECK-NEXT:    [[CLASS:%.*]] = call i1 @llvm.is.fpclass.f32(float [[NINF]], i32 772)
+; CHECK-NEXT:    [[CLASS:%.*]] = call i1 @llvm.is.fpclass.f32(float [[NINF]], i32 256)
 ; CHECK-NEXT:    ret i1 [[CLASS]]
 ;
   %ninf = fadd ninf float %x, 1.0
   %class = call i1 @llvm.is.fpclass.f32(float %ninf, i32 772)
   ret i1 %class
 }
 
 ; --------------------------------------------------------------------