[InstCombine] Remove mul of SPF abs fold

[nikic]

Remove the fold working on abs in SPF representation now that we canonicalize SPF to intrinsics.

This is not strictly NFC because the SPF fold might fire for non-canonical IR due to multi-use, but given the lack of test coverage, I assume this is not important.

[llvmbot]

@llvm/pr-subscribers-llvm-transforms

Author: Nikita Popov (nikic)

Changes

Remove the fold working on abs in SPF representation now that we canonicalize SPF to intrinsics.

This is not strictly NFC because the SPF fold might fire for non-canonical IR due to multi-use, but given the lack of test coverage, I assume this is not important.

---

Full diff: https://github.com/llvm/llvm-project/pull/88675.diff

1 Files Affected:

• (modified) llvm/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp (+6-12)

diff --git a/llvm/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp b/llvm/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp
index 4dc1319f1c437f..ea3443175568c5 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp
@@ -319,19 +319,13 @@ Instruction *InstCombinerImpl::visitMul(BinaryOperator &I) {
   }
 
   // abs(X) * abs(X) -> X * X
-  // nabs(X) * nabs(X) -> X * X
-  if (Op0 == Op1) {
-    Value *X, *Y;
-    SelectPatternFlavor SPF = matchSelectPattern(Op0, X, Y).Flavor;
-    if (SPF == SPF_ABS || SPF == SPF_NABS)
-      return BinaryOperator::CreateMul(X, X);
-
-    if (match(Op0, m_Intrinsic<Intrinsic::abs>(m_Value(X))))
-      return BinaryOperator::CreateMul(X, X);
-  }
+  Value *X;
+  if (Op0 == Op1 &&
+      match(Op0, m_Intrinsic<Intrinsic::abs>(m_Value(X))))
+    return BinaryOperator::CreateMul(X, X);
 
   {
-    Value *X, *Y;
+    Value *Y;
     // abs(X) * abs(Y) -> abs(X * Y)
     if (I.hasNoSignedWrap() &&
         match(Op0,
@@ -344,7 +338,7 @@ Instruction *InstCombinerImpl::visitMul(BinaryOperator &I) {
   }
 
   // -X * C --> X * -C
-  Value *X, *Y;
+  Value *Y;
   Constant *Op1C;
   if (match(Op0, m_Neg(m_Value(X))) && match(Op1, m_Constant(Op1C)))
     return BinaryOperator::CreateMul(X, ConstantExpr::getNeg(Op1C));

[github-actions]

✅ With the latest revision this PR passed the C/C++ code formatter.

[goldsteinn]

Assuming no regression in @dtcxzyw tests, LGTM.

[dtcxzyw]

LGTM.

[dtcxzyw]

We can propagate nsw flag as the following code does.
Alive2: https://alive2.llvm.org/ce/z/uQpZJJ

FYI this pattern is rare: https://dtcxzyw.github.io/llvm-opt-benchmark/coverage/home/dtcxzyw/llvm-project/llvm/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp.html#L321

[AtariDreams]

#88662

For nabs we can propagate nsw if nuw is present see the alive proofs here