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510283
2015 Jun 10
2
[LLVMdev] should InstCombine preserve @llvm.assume?
...e(i1 %1)
ret i32 %sum
}
"opt -instcombine" emits
define i32 @foo(i32 %a, i32 %b) {
%sum = add i32 %a, %b
ret i32 %sum
}
removing the @llvm.assume call so later optimizations won't know sum is
non-negative any more. (Note that the opt I use here is with
http://reviews.llvm.org/D10283 patched. This patch fixes a bug in
ValueTracking).
The reasons that InstCombine removes this assume call are:
1) SimplifyICmpInst proves %1 is true based on the assume call.
2) then, InstCombine (
http://llvm.org/docs/doxygen/html/InstCombineCompares_8cpp_source.html#l02649)
replaces all uses of %...