[llvm-commits] [llvm] r76285 - /llvm/trunk/lib/Transforms/Utils/InlineCost.cpp

[Chris Lattner]

On Jul 17, 2009, at 10:26 PM, Eli Friedman wrote:

> Author: efriedma
> Date: Sat Jul 18 00:26:06 2009
> New Revision: 76285
>
> URL: http://llvm.org/viewvc/llvm-project?rev=76285&view=rev
> Log:
> Fix the inline cost calculation to take into account instructions
> which cannot be folded even if they have constant operands.  
> Significantly
> helps if_spppsubr.c attached to PR4573.

Hi Eli,

This is a great catch.  However, one case that is important to get is  
"load <ptr>" where ptr is a (constant) pointer to a constant global.   
This can lead to serious shrinkage :)

-Chris

>
>
> Modified:
>    llvm/trunk/lib/Transforms/Utils/InlineCost.cpp
>
> Modified: llvm/trunk/lib/Transforms/Utils/InlineCost.cpp
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Utils/InlineCost.cpp?rev=76285&r1=76284&r2=76285&view=diff
>
> = 
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> ======================================================================
> --- llvm/trunk/lib/Transforms/Utils/InlineCost.cpp (original)
> +++ llvm/trunk/lib/Transforms/Utils/InlineCost.cpp Sat Jul 18  
> 00:26:06 2009
> @@ -42,6 +42,13 @@
>       // Figure out if this instruction will be removed due to  
> simple constant
>       // propagation.
>       Instruction &Inst = cast<Instruction>(**UI);
> +
> +      // We can't constant propagate instructions which have  
> effects or
> +      // read memory.
> +      if (Inst.mayReadFromMemory() || Inst.mayHaveSideEffects() ||
> +          isa<AllocationInst>(Inst))
> +        continue;
> +
>       bool AllOperandsConstant = true;
>       for (unsigned i = 0, e = Inst.getNumOperands(); i != e; ++i)
>         if (!isa<Constant>(Inst.getOperand(i)) &&  
> Inst.getOperand(i) != V) {
>
>
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