[PATCH] D153148: [InstCombine] Fold `(-1 + A) & B` into `A ? 0 : B` where A is effectively a bool

[Noah Goldstein via Phabricator via llvm-commits]

goldstein.w.n added inline comments.


================
Comment at: llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp:2601
       A->getType()->isIntOrIntVectorTy(1))
-    return SelectInst::Create(A, Constant::getNullValue(Ty), Op0);
+    return SelectInst::Create(A, Constant::getNullValue(Ty), B);
+
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nikic wrote:
> Please land this code cleanup as a separate NFC commit.
This comment is outstanding.


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Comment at: llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp:2604
+  // (-1 + A) & B --> A ? 0 : B where A is effectively a bool (zext of i1/<N x
+  // i1>, or inst with !range {0, 2}).
+  if (match(&I, m_c_And(m_OneUse(m_Add(m_ZExtOrSelf(m_Value(A)), m_AllOnes())),
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`i1`/`!range {0,2}` isn't really the necessary condition. The necessary condition is `A` is `0` or `1` which can be proven in a lot more cases.

Please also update the title/summary with this precondition of `A` being 0/1.


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D153148/new/

https://reviews.llvm.org/D153148