[PATCH] D63382: [InstCombine] fold a shifted zext to a select

[Roman Lebedev via Phabricator via llvm-commits]

lebedev.ri added a comment.

Don't know if this is the canonicalization we want, but some notes



================
Comment at: llvm/lib/Transforms/InstCombine/InstCombineShifts.cpp:600
+      // shl (zext (i1 X)), ShAmt --> select (X, 0, 1 << ShAmt)
+      if (X->getType()->isIntegerTy(1)) {
+        return SelectInst::Create(X, ConstantInt::get(Ty, 1 << ShAmt),
----------------
vectors of i1 too (`isIntOrIntVectorTy(1)`)


================
Comment at: llvm/lib/Transforms/InstCombine/InstCombineShifts.cpp:601
+      if (X->getType()->isIntegerTy(1)) {
+        return SelectInst::Create(X, ConstantInt::get(Ty, 1 << ShAmt),
+                                  ConstantInt::get(Ty, 0));
----------------
this will overflow, you want 
```
ConstantInt::get(Ty, APInt(Ty->getScalarType()->getBitWidth(), 1) << ShAmt)
```
or something


Repository:
  rG LLVM Github Monorepo

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https://reviews.llvm.org/D63382