[llvm-commits] [llvm] r57342 - in /llvm/trunk: include/llvm/Analysis/EscapeAnalysis.h lib/Analysis/EscapeAnalysis.cpp

[Duncan Sands]

Hi Owen,

> +    // FIXME: Are there any other possible escape points?

if M is a malloced pointer, this would cause M to escape:

if (M & 1)
  bits[0]=1;
if (M & 2)
  bits[1]=1;
if (M & 4)
  bits[2]=1;
...

Export the "bits" array somehow (eg: write to a global,
a parameter, return it).  Then other parts of the program
can reconstruct M from bits, so it would be wrong to
convert it to an alloca.

> +/// escapes - Determines whether the passed allocation can escape from the 
> +/// current function.  It does this by using a simple worklist algorithm to
> +/// search for a path in the def-use graph from the allocation to an
> +/// escape point.

As the above example shows, you also have to watch out for control flow.
This may not involve phi nodes.

Ciao,

Duncan.