[PATCH] D145846: [InstCombine] enhance icmp with sub folds

Fri Apr 14 02:12:17 PDT 2023

Allen added a comment.

https://github.com/llvm/llvm-project/issues/60818

In D145846#4266860 <https://reviews.llvm.org/D145846#4266860>, @bcl5980 wrote:

> How about this pattern ?
> https://alive2.llvm.org/ce/z/Y-Po8g
> Also reduce one usage but it works for any minuend.

Yes, I think this case is similar, but it seems the llvm doesn't have the issue end-to-end for C source,  https://godbolt.org/z/EYMo9bd9c.

================
Comment at: llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp:4096
+  if (match(&I, m_c_ICmp(Pred, m_OneUse(m_Neg(m_Value(X))), m_Deferred(X))) &&
+      (Pred == ICmpInst::ICMP_NE || Pred == ICmpInst::ICMP_EQ)) {
+    Type *Ty = X->getType();
----------------
nikic wrote:
> nikic wrote:
> > Use `ICmpInst::isEquality()`.
> isEquality() means "EQ" or "NE". You don't need to check for ICMP_NE separately.
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