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Add a complex missed optimization opportunity I came across while investigating

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bug 5438.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@88855 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Nick Lewycky 2009-11-15 17:51:23 +00:00
parent e0fb75d586
commit 93f9f7a440
1 changed files with 15 additions and 0 deletions
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15
lib/Target/README.txt
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@ -1719,3 +1719,18 @@ static int foo(const char *X) { return strlen(X); }
int bar() { return foo("abcd"); }
//===---------------------------------------------------------------------===//
InstCombine should use SimplifyDemandedBits to remove the or instruction:
define i1 @test(i8 %x, i8 %y) {
%A = or i8 %x, 1
%B = icmp ugt i8 %A, 3
ret i1 %B
}
Currently instcombine calls SimplifyDemandedBits with either all bits or just
the sign bit, if the comparison is obviously a sign test. In this case, we only
need all but the bottom two bits from %A, and if we gave that mask to SDB it
would delete the or instruction for us.
//===---------------------------------------------------------------------===//