[llvm] [InstCombine] Fold `(op x, ({z,s}ext (icmp eq x, C)))` to select (PR #89020)
Nikita Popov via llvm-commits
llvm-commits at lists.llvm.org
Thu Apr 18 02:58:04 PDT 2024
================
@@ -4734,6 +4734,89 @@ void InstCombinerImpl::tryToSinkInstructionDbgValues(
}
}
+// If we have:
+// `(op X, (zext/sext (icmp eq X, C)))`
+// We can transform it to:
+// `(select (icmp eq X, C), (op C, (zext/sext 1)), (op X, 0))`
+// We do so if the `zext/sext` is one use and `(op X, 0)` simplifies.
+Value *InstCombinerImpl::foldOpOfXWithXEqC(Value *Op, const SimplifyQuery &SQ) {
----------------
nikic wrote:
FWIW, I think the additional complexity is actually quite significant. Doing this for just add is something like:
```
if (match(I, m_c_Add(m_Value(X),
m_ZExt(m_CombineAnd(
m_Value(Cond),
m_ICmp(Pred, m_Deferred(X), m_ImmConstant(C)))))) &&
Pred == ICmpInst::ICMP_EQ)
return Builder.CreateSelect(
Cond, Builder.CreateAdd(C, ConstantInt::get(C->getType(), 1)), X);
```
Generalizing it to other operations is a hundred lines of code here, plus a dozen call sites elsewhere.
https://github.com/llvm/llvm-project/pull/89020
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