[cfe-commits] r94063 - /cfe/trunk/lib/Sema/SemaDecl.cpp

[Chris Lattner]

On Jan 20, 2010, at 6:55 PM, Mike Stump wrote:

> Author: mrs
> Date: Wed Jan 20 20:55:37 2010
> New Revision: 94063
> 
> URL: http://llvm.org/viewvc/llvm-project?rev=94063&view=rev
> Log:
> When checking for unreachable blocks, we can trivially avoid extra
> work, if we know we already marked all blocks as live.
> 

Nice, thanks Mike!

-Chris


> Modified:
>    cfe/trunk/lib/Sema/SemaDecl.cpp
> 
> Modified: cfe/trunk/lib/Sema/SemaDecl.cpp
> URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/lib/Sema/SemaDecl.cpp?rev=94063&r1=94062&r2=94063&view=diff
> 
> ==============================================================================
> --- cfe/trunk/lib/Sema/SemaDecl.cpp (original)
> +++ cfe/trunk/lib/Sema/SemaDecl.cpp Wed Jan 20 20:55:37 2010
> @@ -1310,25 +1310,31 @@
>   New->setAccess(Old->getAccess());
> }
> 
> -static void MarkLive(CFGBlock *e, llvm::BitVector &live) {
> +// MarkLive - Mark all the blocks reachable from e as live.  Returns the total
> +// number of blocks marked live.
> +static unsigned MarkLive(CFGBlock *e, llvm::BitVector &live) {
> +  unsigned count = 0;
>   std::queue<CFGBlock*> workq;
>   // Prep work queue
> +  live.set(e->getBlockID());
> +  ++count;
>   workq.push(e);
>   // Solve
>   while (!workq.empty()) {
>     CFGBlock *item = workq.front();
>     workq.pop();
> -    live.set(item->getBlockID());
>     for (CFGBlock::succ_iterator I=item->succ_begin(),
>            E=item->succ_end();
>          I != E;
>          ++I) {
>       if ((*I) && !live[(*I)->getBlockID()]) {
>         live.set((*I)->getBlockID());
> +        ++count;
>         workq.push(*I);
>       }
>     }
>   }
> +  return count;
> }
> 
> static SourceLocation GetUnreachableLoc(CFGBlock &b) {
> @@ -1432,7 +1438,9 @@
> 
>   llvm::BitVector live(cfg->getNumBlockIDs());
>   // Mark all live things first.
> -  MarkLive(&cfg->getEntry(), live);
> +  if (MarkLive(&cfg->getEntry(), live) == cfg->getNumBlockIDs())
> +    // If there are no dead blocks, we're done.
> +    return;
> 
>   llvm::SmallVector<SourceLocation, 24> lines;
>   // First, give warnings for blocks with no predecessors, as they
> 
> 
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