[PATCH] D52934: [FPEnv] PatternMatcher support for checking FNEG ignoring signed zeros

[Sanjay Patel via Phabricator via llvm-commits]

spatel added inline comments.


================
Comment at: include/llvm/IR/PatternMatch.h:672
+inline BinaryOp_match<cstfp_pred_ty<is_any_zero_fp>, RHS, Instruction::FSub>
+m_ISZFNeg(const RHS &X) {
+  return m_FSub(m_AnyZeroFP(), X);
----------------
Let's use the existing LLVM vocabulary for "ignore signed zero":
"m_FNegNSZ"


================
Comment at: lib/Analysis/InstructionSimplify.cpp:4510-4512
     // We can ignore signed zeros because +-0.0/+-0.0 is NaN and ignored.
-    if ((BinaryOperator::isFNeg(Op0, /*IgnoreZeroSign=*/true) &&
-         BinaryOperator::getFNegArgument(Op0) == Op1) ||
-        (BinaryOperator::isFNeg(Op1, /*IgnoreZeroSign=*/true) &&
-         BinaryOperator::getFNegArgument(Op1) == Op0))
+    if ((match(Op0, m_ISZFNeg(m_Value(X))) && X == Op1) ||
+        (match(Op1, m_ISZFNeg(m_Value(X))) && X == Op0))
----------------
Yes, this works like you're hoping. We use this code pattern all over instsimplify/instcombine.

But we have a matcher API that will shorten this:

```
if (match(Op0, m_FNegNSZ(m_Specific(Op1) || 
    match(Op1, m_FNegNSZ(m_Specific(Op0))))
```


https://reviews.llvm.org/D52934