Remove dead code in instcombine.

Don't replace shifts greater than the type with the maximum shift.

This isn't hit anywhere in the tests, and somewhere else is replacing
these with undef.

llvm-svn: 207000

llvm/lib/Transforms/InstCombine/InstCombineShifts.cpp

@@ -337,21 +337,12 @@ Instruction *InstCombiner::FoldShiftByConstant(Value *Op0, Constant *Op1,
                  GetShiftedValue(Op0, COp1->getZExtValue(), isLeftShift, *this));
   }
 
-
   // See if we can simplify any instructions used by the instruction whose sole
   // purpose is to compute bits we don't care about.
   uint32_t TypeBits = Op0->getType()->getScalarSizeInBits();
 
-  // shl i32 X, 32 = 0 and srl i8 Y, 9 = 0, ... just don't eliminate
-  // a signed shift.
-  //
-  if (COp1->uge(TypeBits)) {
-    if (I.getOpcode() != Instruction::AShr)
-      return ReplaceInstUsesWith(I, Constant::getNullValue(Op0->getType()));
-    // ashr i32 X, 32 --> ashr i32 X, 31
-    I.setOperand(1, ConstantInt::get(I.getType(), TypeBits-1));
-    return &I;
-  }
+  assert(!COp1->uge(TypeBits) &&
+         "Shift over the type width should have been removed already");
 
   // ((X*C1) << C2) == (X * (C1 << C2))
   if (BinaryOperator *BO = dyn_cast<BinaryOperator>(Op0))