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[CVP] Convert an AShr to a LShr if 1st operand is known to be nonnegative.
authorChad Rosier <mcrosier@codeaurora.org>
Wed, 12 Oct 2016 13:41:38 +0000 (13:41 +0000)
committerChad Rosier <mcrosier@codeaurora.org>
Wed, 12 Oct 2016 13:41:38 +0000 (13:41 +0000)
commitc215c3fd143d11f6fd051b5556b04970f9888381
tree875b56195be8bda65f81fc56bbb753a4ceb5b785tree | snapshot
parentb271a58e377f7aeb761945dc02aff7041a1ef44bcommit | diff
[CVP] Convert an AShr to a LShr if 1st operand is known to be nonnegative.

An arithmetic shift can be safely changed to a logical shift if the first
operand is known positive. This allows ComputeKnownBits (and similar analysis)
to determine the sign bit of the shifted value in some cases. In turn, this
allows InstCombine to canonicalize a signed comparison (a > 0) into an equality
check (a != 0).

PR30577

Differential Revision: https://reviews.llvm.org/D25119

llvm-svn: 284013
llvm/lib/Transforms/Scalar/CorrelatedValuePropagation.cpp diff | blob | history
llvm/test/Transforms/CorrelatedValuePropagation/ashr.ll [new file with mode: 0644] blob
Domain: System / Toolchain;