diff options
Diffstat (limited to 'lib/Target/X86/README.txt')
| -rw-r--r-- | lib/Target/X86/README.txt | 19 |
1 files changed, 17 insertions, 2 deletions
diff --git a/lib/Target/X86/README.txt b/lib/Target/X86/README.txt index 3796aac57c..767771f082 100644 --- a/lib/Target/X86/README.txt +++ b/lib/Target/X86/README.txt @@ -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: |