[InstCombine] Remove redundant/bogus mul_with_overflow combines

As pointed out in D60518 folding mulo(%x, undef) to {undef, undef}
isn't correct. As a correct version of this already exists in
InstructionSimplify (https://github.com/llvm-mirror/llvm/blob/bd8056ef326e075cc500f3f0cfcd1193bc200594/lib/Analysis/InstructionSimplify.cpp#L4750-L4757) this is just
dead code though. Drop it together with the mul(%x, 0) -> {0, false}
fold that is also already handled by InstSimplify.

Differential Revision: https://reviews.llvm.org/D60649

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@358339 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/lib/Transforms/InstCombine/InstCombineCompares.cpp b/lib/Transforms/InstCombine/InstCombineCompares.cpp
index 2c7d70e4db4c1752af0ea76e3bbdaa69dff371d7..c73a095804bdd33884369c35cf84ab93d36728a5 100644 (file)
--- a/lib/Transforms/InstCombine/InstCombineCompares.cpp
+++ b/lib/Transforms/InstCombine/InstCombineCompares.cpp
@@ -4011,14 +4011,6 @@ bool InstCombiner::OptimizeOverflowCheck(OverflowCheckFlavor OCF, Value *LHS,
 
   case OCF_UNSIGNED_MUL:
   case OCF_SIGNED_MUL: {
-    // X * undef -> undef
-    if (isa<UndefValue>(RHS))
-      return SetResult(RHS, UndefValue::get(Builder.getInt1Ty()), false);
-
-    // X * 0 -> {0, false}
-    if (match(RHS, m_Zero()))
-      return SetResult(RHS, Builder.getFalse(), false);
-
     // X * 1 -> {X, false}
     if (match(RHS, m_One()))
       return SetResult(LHS, Builder.getFalse(), false);