Question on GIMPLE semantics and EH

[Richard Henderson]

On Fri, Aug 13, 2004 at 08:34:51AM -0400, Richard Kenner wrote:
> Suppose I have something like:
> 
> 	foo = 0;
> 	...
> 	foo = some_function_call_that_may_throw ( ...);
> 
> in one basic block and then in the exception handler, we have:
> 
> 	bar = foo;
> 
> As I understand it, the semantics of GIMPLE is that the second assignment to
> FOO may not happen, but if it doesn't, then the value must remain 0.

Not exactly.  It depends on the type of foo.  From the assignment
from zero, I assume it's scalar.  Which means that the value always
dies at the function call.  Which is why you should *not* have seen
an assignment to foo directly out of the .10.gimple dump -- it should
have been a temporary.

I presume the temporary name got folded away by the first copyrename
pass, but that in the dump you're looking at, the two occurrences of
foo have different ssa names.

> copyrename2 is replacing the second assignment's LHS with BAR.

No.  It's replacing the base of the SSA_NAME, which is absolutely
not the same thing.

Do not drop ssa names from problems you report.  It only confuses
the issue.

> What's going wrong here?

Who knows.  Give us a proper bug report and we might be able to help.


r~