llvm-project

Commit Graph

Author	SHA1	Message	Date
Chad Rosier	c215c3fd14	[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	2016-10-12 13:41:38 +00:00

Author

SHA1

Message

Date

Chad Rosier

c215c3fd14

[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

2016-10-12 13:41:38 +00:00

1 Commits