[PATCH] D108485: [DSE] Check post-dominance for malloc+memset->calloc transform.

Fri Aug 20 15:18:46 PDT 2021

xbolva00 added inline comments.

================
Comment at: llvm/test/Transforms/DeadStoreElimination/noop-stores.ll:415
 ; CHECK-NEXT:    [[CMP:%.*]] = icmp eq i8* [[CALL]], null
 ; CHECK-NEXT:    br i1 [[CMP]], label [[CLEANUP:%.*]], label [[IF_END:%.*]]
 ; CHECK:       if.end:
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asbirlea wrote:
> xbolva00 wrote:
> > I would rather see better fix, so this motivating case still works (allow 'ptr compared with NULL'). Othewise I see no value from this optimization at all and it should be just removed from DSE.
> > 
> > I am somewhat scared that people talking about this pattern
> > ```
> > memset(malloc(size), 0, size)
> > ```
> > 
> > not suprised that why there are so many nasty bugs/exploits in C codebases.
> > I would rather see better fix, so this motivating case still works (allow 'ptr compared with NULL'). Othewise I see no value from this optimization at all and it should be just removed from DSE.
> > 
> Sure, revert is a viable option while looking to add the 'ptr compared with NULL' check, as that's not so straightforward.
But probably we should just take your patch, to avoid regression as SLC's transformation was removed as DSE-based one was implemented.

Repository:
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  https://reviews.llvm.org/D108485/new/

https://reviews.llvm.org/D108485