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I think instcombine should unconditionally do this xform. 

llvm-svn: 73471
This commit is contained in:
Chris Lattner 2009-06-16 06:11:35 +00:00
parent 06310bf178
commit aba55a69b1
1 changed files with 17 additions and 2 deletions
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19
llvm/lib/Target/X86/README.txt
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@ -1858,8 +1858,23 @@ Ideal output:
setne %al
ret
We could do this transformation in instcombine, but it's only clearly
beneficial on platforms with a test instruction.
This should definitely be done in instcombine, canonicalizing the range
condition into a != condition. We get this IR:
define i32 @a(i32 %x) nounwind readnone {
entry:
%0 = and i32 %x, 127 ; <i32> [#uses=1]
%1 = icmp ugt i32 %0, 31 ; <i1> [#uses=1]
%2 = zext i1 %1 to i32 ; <i32> [#uses=1]
ret i32 %2
}
Instcombine prefers to strength reduce relational comparisons to equality
comparisons when possible, this should be another case of that. This could
be handled pretty easily in InstCombiner::visitICmpInstWithInstAndIntCst, but it
looks like InstCombiner::visitICmpInstWithInstAndIntCst should really already
be redesigned to use ComputeMaskedBits and friends.
//===---------------------------------------------------------------------===//
Testcase: