ADT: Replace FPClassTest fabs with inverse_fabs and unknown_sign (#66390)

Author: arsenm

llvm/include/llvm/ADT/FloatingPointMode.h

@@ -269,8 +269,12 @@ LLVM_DECLARE_ENUM_AS_BITMASK(FPClassTest, /* LargestValue */ fcPosInf);
 /// Return the test mask which returns true if the value's sign bit is flipped.
 FPClassTest fneg(FPClassTest Mask);
 
-/// Return the test mask which returns true if the value's sign bit is cleared.
-FPClassTest fabs(FPClassTest Mask);
+/// Return the test mask which returns true after fabs is applied to the value.
+FPClassTest inverse_fabs(FPClassTest Mask);
+
+/// Return the test mask which returns true if the value could have the same set
+/// of classes, but with a different sign.
+FPClassTest unknown_sign(FPClassTest Mask);
 
 /// Write a human readable form of \p Mask to \p OS
 raw_ostream &operator<<(raw_ostream &OS, FPClassTest Mask);

llvm/lib/Support/FloatingPointMode.cpp

@@ -32,7 +32,7 @@ FPClassTest llvm::fneg(FPClassTest Mask) {
   return NewMask;
 }
 
-FPClassTest llvm::fabs(FPClassTest Mask) {
+FPClassTest llvm::inverse_fabs(FPClassTest Mask) {
   FPClassTest NewMask = Mask & fcNan;
   if (Mask & fcPosZero)
     NewMask |= fcZero;
@@ -45,6 +45,19 @@ FPClassTest llvm::fabs(FPClassTest Mask) {
   return NewMask;
 }
 
+FPClassTest llvm::unknown_sign(FPClassTest Mask) {
+  FPClassTest NewMask = Mask & fcNan;
+  if (Mask & fcZero)
+    NewMask |= fcZero;
+  if (Mask & fcSubnormal)
+    NewMask |= fcSubnormal;
+  if (Mask & fcNormal)
+    NewMask |= fcNormal;
+  if (Mask & fcInf)
+    NewMask |= fcInf;
+  return NewMask;
+}
+
 // Every bitfield has a unique name and one or more aliasing names that cover
 // multiple bits. Names should be listed in order of preference, with higher
 // popcounts listed first.

llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp

@@ -899,7 +899,7 @@ Instruction *InstCombinerImpl::foldIntrinsicIsFPClass(IntrinsicInst &II) {
 
   Value *FAbsSrc;
   if (match(Src0, m_FAbs(m_Value(FAbsSrc)))) {
-    II.setArgOperand(1, ConstantInt::get(Src1->getType(), fabs(Mask)));
+    II.setArgOperand(1, ConstantInt::get(Src1->getType(), inverse_fabs(Mask)));
     return replaceOperand(II, 0, FAbsSrc);
   }