[PATCH] D63652: [InstCombine] (1 << (C - x)) -> ((1 << C) >> x) if C is bitwidth - 1

[Nikita Popov via Phabricator via llvm-commits]

nikic added inline comments.


================
Comment at: lib/Transforms/InstCombine/InstCombineShifts.cpp:677
+  // (1 << (C - x)) -> ((1 << C) >> x) if C is bitwidth - 1
+  if (match(Op0, m_APInt(ShlOp0)) && ShlOp0->getSExtValue() == 1 &&
+      match(Op1, m_Sub(m_APInt(C), m_Value(X))) &&
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lebedev.ri wrote:
> nikic wrote:
> > getSExtValue will assert if the value is too large. You can use `ShlOp0->isOneValue()` here.
> m_One()
Or maybe even simpler, use `match(Op0, m_One())`.


CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D63652/new/

https://reviews.llvm.org/D63652