Revert r367891 - "[InstCombine] combine mul+shl separated by zext"

This reverts commit 5dbb90bfe14ace30224239cac7c61a1422fa5144.

As noted in the post-commit thread for r367891, this can create
a multiply that is lowered to a libcall that may not exist.

We need to improve the backend decomposition for integer multiply
before trying to re-land this (if it's still worthwhile after
doing the backend work).

llvm-svn: 369174

1 files changed, 2 insertions, 13 deletions

diff --git a/llvm/lib/Transforms/InstCombine/InstCombineShifts.cpp b/llvm/lib/Transforms/InstCombine/InstCombineShifts.cpp
index db6e4951a7a..2891edd4502 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineShifts.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineShifts.cpp
@@ -763,25 +763,14 @@ Instruction *InstCombiner::visitShl(BinaryOperator &I) {
     unsigned ShAmt = ShAmtAPInt->getZExtValue();
     unsigned BitWidth = Ty->getScalarSizeInBits();
 
+    // shl (zext X), ShAmt --> zext (shl X, ShAmt)
+    // This is only valid if X would have zeros shifted out.
     Value *X;
     if (match(Op0, m_OneUse(m_ZExt(m_Value(X))))) {
       unsigned SrcWidth = X->getType()->getScalarSizeInBits();
-      // shl (zext X), ShAmt --> zext (shl X, ShAmt)
-      // This is only valid if X would have zeros shifted out.
       if (ShAmt < SrcWidth &&
           MaskedValueIsZero(X, APInt::getHighBitsSet(SrcWidth, ShAmt), 0, &I))
         return new ZExtInst(Builder.CreateShl(X, ShAmt), Ty);
-
-      // shl (zext (mul MulOp, C2)), ShAmt --> mul (zext MulOp), (C2 << ShAmt)
-      // This is valid if the high bits of the wider multiply are shifted out.
-      Value *MulOp;
-      const APInt *C2;
-      if (ShAmt >= (BitWidth - SrcWidth) &&
-          match(X, m_Mul(m_Value(MulOp), m_APInt(C2)))) {
-        Value *Zext = Builder.CreateZExt(MulOp, Ty);
-        Constant *NewMulC = ConstantInt::get(Ty, C2->zext(BitWidth).shl(ShAmt));
-        return BinaryOperator::CreateMul(Zext, NewMulC);
-      }
     }
 
     // (X >> C) << C --> X & (-1 << C)