[llvm-commits] patch: don't remove CMP if used by instruction that both reads and modifies EFLAGS

[Nick Lewycky]

This patch fixes PR13475, a miscompile in unzip. The problem manifested in
code like:

        subl    %esi, %eax
        cmpl    %edx, %esi
        sbbb    %cl, %cl

where we concluded that it was safe to remove the cmp without changing the
sbb. Please review!

Nick

PS. There's an optimization opportunity here, to turn the cmp+sbbb into a
setnc.
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