[InstCombine] remove an icmp fold that is already handled by InstSimplify

Specifically, this is done near the end of "SimplifyICmpInst" using
computeKnownBits() as the broader solution. There are even vector
tests (yay!) for this in test/Transforms/InstSimplify/compare.ll.

I considered putting an assert here instead of just deleting, but
then we could assert every possible fold in InstSimplify in
InstCombine, so...less is more?

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@279300 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/lib/Transforms/InstCombine/InstCombineCompares.cpp b/lib/Transforms/InstCombine/InstCombineCompares.cpp
index 2558773..f9a7eb2 100644 (file)
--- a/lib/Transforms/InstCombine/InstCombineCompares.cpp
+++ b/lib/Transforms/InstCombine/InstCombineCompares.cpp
@@ -2009,16 +2009,6 @@ Instruction *InstCombiner::foldICmpShlConstant(ICmpInst &Cmp, Instruction *Shl,
   ICmpInst::Predicate Pred = Cmp.getPredicate();
   Value *X = Shl->getOperand(0);
   if (Cmp.isEquality()) {
-    // If we are comparing against bits always shifted out, the comparison
-    // cannot succeed.
-    Constant *Comp =
-        ConstantExpr::getShl(ConstantExpr::getLShr(RHS, ShAmt), ShAmt);
-    if (Comp != RHS) { // Comparing against a bit that we know is zero.
-      bool IsICMP_NE = Pred == ICmpInst::ICMP_NE;
-      Constant *Cst = Builder->getInt1(IsICMP_NE);
-      return replaceInstUsesWith(Cmp, Cst);
-    }
-
     // If the shift is NUW, then it is just shifting out zeros, no need for an
     // AND.
     if (cast<BinaryOperator>(Shl)->hasNoUnsignedWrap())