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branch "br i1 %x, label %if_true, label %if_false" then it replaces "%x" with "true" in places only reachable via the %if_true arm, and with "false" in places only reachable via the %if_false arm. Except that actually it doesn't: if value numbering shows that %y is equal to %x then, yes, %y will be turned into true/false in this way, but any occurrences of %x itself are not transformed. Fix this. What's more, it's often the case that %x is an equality comparison such as "%x = icmp eq %A, 0", in which case every occurrence of %A that is only reachable via the %if_true arm can be replaced with 0. Implement this and a few other variations on this theme. This reduces the number of lines of LLVM IR in "GCC as one big file" by 0.2%. It has a bigger impact on Ada code, typically reducing the number of lines of bitcode by around 0.4% by removing repeated compiler generated checks. Passes the LLVM nightly testsuite and the Ada ACATS testsuite. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@141177 91177308-0d34-0410-b5e6-96231b3b80d8
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