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Re: [PATCH] fix a couple of bugs in const string folding (PR 86532)

On Tue, 17 Jul 2018, Martin Sebor wrote:

> The attached update takes care of a couple of problems pointed
> out by Bernd Edlinger in his comments on the bug.  The ICE he
> mentioned in comment #20 was due mixing sizetype, ssizetype,
> and size_type_node in c_strlen().  AFAICS, some of it predates
> the patch but my changes made it worse and also managed trigger
> it.

+        has no internal zero bytes.  If the offset falls within the 
+        of the string subtract the offset from the length of the string,
+        and return that.  Otherwise the length is zero.  Take care to
+        use SAVE_EXPR in case the OFFSET has side-effects.  */
+      tree offsave = TREE_SIDE_EFFECTS (byteoff) ? save_expr (byteoff) :
+      offsave = fold_convert (ssizetype, offsave);
+      tree condexp = fold_build2_loc (loc, LE_EXPR, boolean_type_node,
+                                     build_int_cst (ssizetype, len *
+      tree lenexp = size_diffop_loc (loc, ssize_int (strelts * eltsize),
+      return fold_build3_loc (loc, COND_EXPR, ssizetype, condexp, lenexp,
+                             build_zero_cst (ssizetype));

in what case are you expecting to return an actual COND_EXRP and
why is that useful?  You return a signed value but bother to
guard it so it is never less than zero.  Why?  Why not simply
return the difference as you did before but with the side-effects
properly handled?

> On 07/17/2018 09:19 AM, Martin Sebor wrote:
> > My enhancement to extract constant strings out of complex
> > aggregates committed last week introduced a couple of bugs in
> > dealing with non-constant indices and offsets.  One of the bugs
> > was fixed earlier today (PR 86528) but another one remains.  It
> > causes strlen (among other functions) to incorrectly fold
> > expressions involving a non-constant index into an array of
> > strings by treating the index the same as a non-consatnt
> > offset into it.
> > 
> > The non-constant index should either prevent the folding, or it
> > needs to handle it differently from an offset.
> > 
> > The attached patch takes the conservative approach of avoiding
> > the folding in this case.  The remaining changes deal with
> > the fallout from the fix.
> > 
> > Tested on x86_64-linux.
> > 
> > Martin
> > 

Richard Biener <>
SUSE LINUX GmbH, GF: Felix Imendoerffer, Jane Smithard, Graham Norton, HRB 21284 (AG Nuernberg)

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