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

[Akira Hatanaka]

================
Comment at: lib/Transforms/InstCombine/InstCombineCompares.cpp:2122
@@ +2121,3 @@
+  case ICmpInst::ICMP_ULT:
+    // Recognize pattern:
+    //   mulval = mul(zext A, zext B)
----------------
If the comparison is ULT, shouldn't it check whether the constant operand is maxVal + 1 instead of maxVal? Otherwise, the result will be incorrect for a code like this:

if (a * b < 0xffffffff)
  ...


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