On Fri, 1 Nov 2024, Jan Hubicka wrote:
> > On Fri, Nov 01, 2024 at 11:39:13AM +0100, Jan Hubicka wrote:
> > > The testcase does:
> > > /* { dg-additional-options "-O3 -fsanitize=undefined" } */
> > >
> > > void memory_exhausted();
> > > void memcheck(void *ptr) {
> > > if (ptr) /* { dg-warning "leak" } */
> > > memory_exhausted();
> > > }
> > >
> > > int emalloc(int size) { memcheck(__builtin_malloc(size)); } /* {
> > > dg-message "allocated here" } */
> > > int main() { int max_envvar_len = emalloc(max_envvar_len + 1); } /* {
> > > dg-message "use of uninitialized value 'max_envvar_len'" } */
> >
> > The PR was an ICE fix, so I think it is ok to say add -fno-allocation-dce
> > or somehow arrange in the source for the call not to be optimized away,
> > as long as it still ICEs in r12-3094 and succeeds with r12-3095 after
> > that change.
> >
> > Generally regarding warnings, if the compiler optimizes away the allocation
> > altogether, there will be no leak from it, so I think the optimization is
> > fine.
>
> I also thin it is OK to optimize here.
> Currently there is -fno option to disable optimization of malloc/free
> pairs. -fno-allocation-dce handles only new/delete. I am not sure why
> it was added for C++ only. So in the other testcase compensation I
> simply used -fno-tree-dce which would work here too.
I think we should move -fno-allocation-dce to the middle-end and disable
malloc/free pair elision when set (not sure about stack-save/restore
pairs) instead.
Btw, did you check what happens when doing new/delete without nothrow()
and either external or internal EH? I think optimizing is OK in all
cases, but I guess EH edges will prevent the optimization?
Richard.
> Perhaps I can add -fno-malloc-dce to handle the C library variants
> (malloc/calloc/strdup/strndup). I also think I can quite easilly handle
> realloc by combining free and malloc logic together.
>
> Honza
> >
> > Jakub
> >
>
--
Richard Biener <[email protected]>
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