[llvm-commits] [llvm] r71688 - /llvm/trunk/lib/Transforms/Utils/SimplifyCFG.cpp

[Chris Lattner]

On May 13, 2009, at 11:25 AM, Dale Johannesen wrote:

> Author: johannes
> Date: Wed May 13 13:25:07 2009
> New Revision: 71688
>
> URL: http://llvm.org/viewvc/llvm-project?rev=71688&view=rev
> Log:
> Don't generate a select whose operand is load of a weak
> external.  These may have address 0 and are not safe
> to execute unconditionally.

Hi Dale,

Thanks for working on this, but I don't think that this is sufficient:  
it will fail for getelementptr constant exprs of a weak global.  I  
think this should probably use something like  
isSafeToLoadUnconditionally in instcombine.  Maybe that function  
should move to transforms/utils.  Also, testcase? :)

-Chris

>
>
>
> Modified:
>    llvm/trunk/lib/Transforms/Utils/SimplifyCFG.cpp
>
> Modified: llvm/trunk/lib/Transforms/Utils/SimplifyCFG.cpp
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Utils/SimplifyCFG.cpp?rev=71688&r1=71687&r2=71688&view=diff
>
> = 
> = 
> = 
> = 
> = 
> = 
> = 
> = 
> ======================================================================
> --- llvm/trunk/lib/Transforms/Utils/SimplifyCFG.cpp (original)
> +++ llvm/trunk/lib/Transforms/Utils/SimplifyCFG.cpp Wed May 13  
> 13:25:07 2009
> @@ -18,6 +18,7 @@
> #include "llvm/IntrinsicInst.h"
> #include "llvm/Type.h"
> #include "llvm/DerivedTypes.h"
> +#include "llvm/GlobalVariable.h"
> #include "llvm/Support/CFG.h"
> #include "llvm/Support/Debug.h"
> #include "llvm/Analysis/ConstantFolding.h"
> @@ -393,6 +394,11 @@
>         if (!isa<AllocaInst>(I->getOperand(0)) &&
>             !isa<Constant>(I->getOperand(0)))
>           return false;
> +        // External weak globals may have address 0, so we can't  
> load them.
> +        if (GlobalVariable* GV= dyn_cast<GlobalVariable>(I- 
> >getOperand(0))) {
> +          if (GV->hasExternalWeakLinkage())
> +            return false;
> +        }
>
>         // Finally, we have to check to make sure there are no  
> instructions
>         // before the load in its basic block, as we are going to  
> hoist the loop
>
>
> _______________________________________________
> llvm-commits mailing list
> llvm-commits at cs.uiuc.edu
> http://lists.cs.uiuc.edu/mailman/listinfo/llvm-commits