[llvm-commits] [llvm] r148941 - in /llvm/trunk: lib/Analysis/InlineCost.cpp test/Transforms/Inline/alloca-bonus.ll

[Nick Lewycky]

Eli Friedman wrote:
> On Wed, Jan 25, 2012 at 12:27 AM, Nick Lewycky<nicholas at mxc.ca>  wrote:
>> Author: nicholas
>> Date: Wed Jan 25 02:27:40 2012
>> New Revision: 148941
>>
>> URL: http://llvm.org/viewvc/llvm-project?rev=148941&view=rev
>> Log:
>> Support pointer comparisons against constants, when looking at the inline-cost
>> savings from a pointer argument becoming an alloca. Sometimes callees will even
>> compare a pointer to null and then branch to an otherwise unreachable block!
>> Detect these cases and compute the number of saved instructions, instead of
>> bailing out and reporting no savings.
>
> [Comments inlined.]
>
>> +      } else if (ICmpInst *ICI = dyn_cast<ICmpInst>(I)) {
>> +        if (!isa<Constant>(ICI->getOperand(1)))
>> +          return 0;
>> +        ICmpInsts.push_back(ICI);
>
> You probably want to restrict this to equality comparisons; I don't
> think we fold relational comparisons between an alloca and a constant
> in general.

We do. This fits in with the rule that you aren't allowed to guess an 
alloca.

>> +        if (BranchInst *BI = dyn_cast<BranchInst>(I)) {
>> +          BasicBlock *BB = BI->getSuccessor(Result ? 0 : 1);
>> +          if (BB->getSinglePredecessor())
>> +            Reduction += InlineConstants::InstrCost * BB->size();
>
> Shouldn't you use NumBBInsts[BB] rather than BB->size()?

Good catch! Fixed in r148964.

Nick