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InstSimplify: Simplify (X - (0 - Y)) if the second sub is NUW
authorDavid Majnemer <david.majnemer@gmail.com>
Thu, 31 Jul 2014 04:49:18 +0000 (04:49 +0000)
committerDavid Majnemer <david.majnemer@gmail.com>
Thu, 31 Jul 2014 04:49:18 +0000 (04:49 +0000)
commitec7ee070369dd4074f7ad3ac4555ebb9421b8c1a
tree1a7b2a9d81e7dec1720cc2832cb853ff51eee2b8tree | snapshot
parentd1d53e81f61d4b8379d1c06bb8d3662694168c05commit | diff
InstSimplify: Simplify (X - (0 - Y)) if the second sub is NUW

If the NUW bit is set for 0 - Y, we know that all values for Y other
than 0 would produce a poison value.  This allows us to replace (0 - Y)
with 0 in the expression (X - (0 - Y)) which will ultimately leave us
with X.

This partially fixes PR20189.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@214384 91177308-0d34-0410-b5e6-96231b3b80d8
lib/Analysis/InstructionSimplify.cpp diff | blob | history
test/Transforms/InstSimplify/AndOrXor.ll diff | blob | history
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