[PATCH] D47980: [InstCombine] Fold (x << y) >> y -> x & (-1 >> y)
Sanjay Patel via Phabricator via llvm-commits
llvm-commits at lists.llvm.org
Sun Jun 10 10:03:58 PDT 2018
spatel accepted this revision.
spatel added a comment.
This revision is now accepted and ready to land.
LGTM.
================
Comment at: lib/Transforms/InstCombine/InstCombineShifts.cpp:732-735
// (X << C1) >>u C2 --> (X >>u (C2 - C1)) & (-1 >> C2)
Value *NewLShr = Builder.CreateLShr(X, ShiftDiff, "", I.isExact());
APInt Mask(APInt::getLowBitsSet(BitWidth, BitWidth - ShAmt));
return BinaryOperator::CreateAnd(NewLShr, ConstantInt::get(Ty, Mask));
----------------
As with D47981, we could consolidate this, but the constant version doesn't need the one-use check.
I think it's fine either way, but let's keep both patches consistent in their structure.
Repository:
rL LLVM
https://reviews.llvm.org/D47980
More information about the llvm-commits
mailing list