[PATCH] [Instcombine] Recognize test for overflow in integer multiplication.

[Serge Pavlov]

sepavloff added you to the CC list for the revision "[Instcombine] Recognize test for overflow in integer multiplication.".

If multiplication involves zero-extended arguments and the result is
compared as in the patterns:

    %mul32 = trunc i64 %mul64 to i32
    %zext = zext i32 %mul32 to i64
    %overflow = icmp ne i64 %mul64, %zext
or
    %overflow = icmp ugt i64 %mul64 , 0xffffffff

then the multiplication may be replaced by call to umul.with.overflow.
This change fixes PR4917 and PR4918.

http://llvm-reviews.chandlerc.com/D2814

Files:
  lib/Transforms/InstCombine/InstCombineCompares.cpp
  test/Transforms/InstCombine/overflow-mul.ll
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