[InstCombine] Add support for ret nofpclass

Author: dtcxzyw

llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp

@@ -12,6 +12,7 @@
 
 #include "InstCombineInternal.h"
 #include "llvm/ADT/APInt.h"
+#include "llvm/ADT/FloatingPointMode.h"
 #include "llvm/ADT/STLExtras.h"
 #include "llvm/ADT/SmallVector.h"
 #include "llvm/Analysis/AssumptionCache.h"
@@ -2853,6 +2854,9 @@ static bool ignoreSignBitOfNaN(Instruction &I) {
   case Instruction::Select:
   case Instruction::PHI:
     return false;
+  case Instruction::Ret:
+    return I.getFunction()->getAttributes().getRetNoFPClass() &
+           FPClassTest::fcNan;
   case Instruction::Call:
   case Instruction::Invoke: {
     if (auto *II = dyn_cast<IntrinsicInst>(User)) {

llvm/test/Transforms/InstCombine/fabs.ll

@@ -1380,6 +1380,17 @@ define void @test_fabs_used_by_nofpclass_nan(float %x) {
   ret void
 }
 
+define nofpclass(nan) float @test_fabs_used_by_ret_nofpclass_nan(float %x) {
+; CHECK-LABEL: @test_fabs_used_by_ret_nofpclass_nan(
+; CHECK-NEXT:    [[SEL:%.*]] = call nsz float @llvm.fabs.f32(float [[X:%.*]])
+; CHECK-NEXT:    ret float [[SEL]]
+;
+  %cmp = fcmp oge float %x, 0.000000e+00
+  %neg = fneg float %x
+  %sel = select nsz i1 %cmp, float %x, float %neg
+  ret float %sel
+}
+
 define i32 @test_fabs_used_fptosi(float %x) {
 ; CHECK-LABEL: @test_fabs_used_fptosi(
 ; CHECK-NEXT:    [[SEL:%.*]] = call float @llvm.fabs.f32(float [[X:%.*]])