[llvm-commits] CVS: llvm/lib/Transforms/Scalar/InstructionCombining.cpp

[Chris Lattner]

> Index: llvm/lib/Transforms/Scalar/InstructionCombining.cpp
> diff -u llvm/lib/Transforms/Scalar/InstructionCombining.cpp:1.687  
> llvm/lib/Transforms/Scalar/InstructionCombining.cpp:1.688
> --- llvm/lib/Transforms/Scalar/InstructionCombining.cpp:1.687	Sun  
> Mar 25 00:01:29 2007
> +++ llvm/lib/Transforms/Scalar/InstructionCombining.cpp	Sun Mar 25  
> 00:33:51 2007
> @@ -540,8 +540,9 @@
>        if (I->getOpcode() == Instruction::Shl)
>          if ((CST = dyn_cast<ConstantInt>(I->getOperand(1)))) {
>            // The multiplier is really 1 << CST.
> -          Constant *One = ConstantInt::get(V->getType(), 1);
> -          CST = cast<ConstantInt>(ConstantExpr::getShl(One, CST));
> +          APInt Multiplier(V->getType()->getPrimitiveSizeInBits(),  
> 0);
> +          Multiplier.set(CST->getZExtValue()); // set bit is == 1  
> << CST

This doesn't seem safe.  Won't getZextValue assert if CST is > 64 bits?

Also, I don't understand the gymnastics you're doing with Multiplier.

> +          CST = ConstantInt::get(Multiplier);
>            return I->getOperand(0);
>          }
>      }
> @@ -558,14 +559,31 @@
>    return false;
>  }
>
> +/// AddOne - Add one to a ConstantInt
>  static ConstantInt *AddOne(ConstantInt *C) {
> +  APInt One(C->getType()->getPrimitiveSizeInBits(),1);
> +  return ConstantInt::get(C->getValue() + One);
>  }
> +/// SubOne - Subtract one from a ConstantInt
>  static ConstantInt *SubOne(ConstantInt *C) {

Shouldn't these use ++/-- on APInt?  That seems more efficient.

> @@ -2188,14 +2203,12 @@
>
>    ConstantInt *C1;
>    if (Value *X = dyn_castFoldableMul(Op0, C1)) {
> -    if (X == Op1) { // X*C - X --> X * (C-1)
> -      Constant *CP1 = ConstantExpr::getSub(C1, ConstantInt::get 
> (I.getType(),1));
> -      return BinaryOperator::createMul(Op1, CP1);
> -    }
> +    if (X == Op1)  // X*C - X --> X * (C-1)
> +      return BinaryOperator::createMul(Op1, SubOne(C1));

I like this set of changes, much cleaner.

-Chris