ADT: Replace FPClassTest fabs with inverse_fabs and unknown_sign

[arsenm]

The names are confusing. It's supposed to return the possible classes for the source value of a fabs. Some places were using fneg as a way to express unknown sign, but it's clearer to have something separate for this.

unknown_sign will be used in a subsequent patch and avoids a small bug in copysign handling.

[llvmbot]

@llvm/pr-subscribers-llvm-transforms

Changes

The names are confusing. It's supposed to return the possible classes for the source value of a fabs. Some places were using fneg as a way to express unknown sign, but it's clearer to have something separate for this.

unknown_sign will be used in a subsequent patch and avoids a small bug in copysign handling.

Full diff: https://github.com/llvm/llvm-project/pull/66390.diff

3 Files Affected:

• (modified) llvm/include/llvm/ADT/FloatingPointMode.h (+6-2)
• (modified) llvm/lib/Support/FloatingPointMode.cpp (+14-1)
• (modified) llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp (+1-1)

diff --git a/llvm/include/llvm/ADT/FloatingPointMode.h b/llvm/include/llvm/ADT/FloatingPointMode.h
index d80a811fd447a78..468de085d1bede4 100644
--- a/llvm/include/llvm/ADT/FloatingPointMode.h
+++ b/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);
diff --git a/llvm/lib/Support/FloatingPointMode.cpp b/llvm/lib/Support/FloatingPointMode.cpp
index 9543884ff46edd5..5a2836eb8243422 100644
--- a/llvm/lib/Support/FloatingPointMode.cpp
+++ b/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.
diff --git a/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp b/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
index 17cfd90ac209392..c6100f24b0507de 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
+++ b/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);
   }
 

[RKSimon]

LGTM - cheers