[InstSimplify] analyze (optionally casted) icmps to eliminate obviously false logic (PR27869)

By moving this transform to InstSimplify from InstCombine, we sidestep the problem/question
raised by PR27869:
https://llvm.org/bugs/show_bug.cgi?id=27869
...where InstCombine turns an icmp+zext into a shift causing us to miss the fold.

Credit to David Majnemer for a draft patch of the changes to InstructionSimplify.cpp.

Differential Revision: http://reviews.llvm.org/D21512

llvm-svn: 273200

1 files changed, 0 insertions, 10 deletions

diff --git a/llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp b/llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
index 5c0caa1cbfd..e518db13a7f 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
@@ -968,16 +968,6 @@ Value *InstCombiner::FoldAndOfICmps(ICmpInst *LHS, ICmpInst *RHS) {
       RHSCC == ICmpInst::ICMP_SGE || RHSCC == ICmpInst::ICMP_SLE)
     return nullptr;
 
-  // Make a constant range that's the intersection of the two icmp ranges.
-  // If the intersection is empty, we know that the result is false.
-  ConstantRange LHSRange =
-      ConstantRange::makeAllowedICmpRegion(LHSCC, LHSCst->getValue());
-  ConstantRange RHSRange =
-      ConstantRange::makeAllowedICmpRegion(RHSCC, RHSCst->getValue());
-
-  if (LHSRange.intersectWith(RHSRange).isEmptySet())
-    return ConstantInt::get(CmpInst::makeCmpResultType(LHS->getType()), 0);
-
   // We can't fold (ugt x, C) & (sgt x, C2).
   if (!PredicatesFoldable(LHSCC, RHSCC))
     return nullptr;