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Author SHA1 Message Date
Simon Pilgrim 05ab8ffc7e [DAGCombiner] Try to use SelectionDAG::isKnownToBeAPowerOfTwo instead of just APInt::isPowerOf2 
Generalize sdiv/udiv/srem/urem combines using APInt::isPowerOf2, which only works for const/splat-const values, to call SelectionDAG::isKnownToBeAPowerOfTwo instead which recognises many more cases.

Added a DAGCombiner::BuildLogBase2 helper since PowerOf2 combines often involve taking the log2 of such a value.

Differential Revision: https://reviews.llvm.org/D27714

llvm-svn: 289654
 2016-12-14 15:08:13 +00:00
Matthias Braun 152e7c8b12 VirtRegMap: Replace some identity copies with KILL instructions. 
An identity COPY like this:
   %AL = COPY %AL, %EAX<imp-def>
has no semantic effect, but encodes liveness information: Further users
of %EAX only depend on this instruction even though it does not define
the full register.

Replace the COPY with a KILL instruction in those cases to maintain this
liveness information. (This reverts a small part of r238588 but this
time adds a comment explaining why a KILL instruction is useful).

llvm-svn: 274952
 2016-07-09 00:19:07 +00:00
Sanjay Patel c48a879ef8 [x86] add tests for urem lowering 
llvm-svn: 270096
 2016-05-19 18:57:54 +00:00