On Wed, Feb 26, 2025 at 10:58:26AM +0100, Richard Biener wrote:
> > This PR is about ubsan error on the c - cx1 + cy1 evaluation in the first
> > hunk.
> >
> > The following patch hopefully fixes that by doing the additions/subtractions
> > in poly_uint64 rather than poly_int64. Or shall we instead perform it in
> > offset_int and watch for overflows and punt somehow for those?
>
> I think when we have the offset computation overflow ignoring such
> overflow will make the memrefs_conflict_p give possibly wrong
> answers. In the PR you say cselib now has those
> -9223372036854775807ish offsets from sp, why does it do alias queries
> with those clearly invalid offsets?
It wants to have a MEM which overlaps anything below the stack.
So, uses for stack grows down and non-biased stack sp - PTRDIFF_MAX with
PTRDIFF_MAX MEM_SIZE as an approximation to that.
> So yes, I think we need to punt on overflow. Using poly_offset_int
> should work but it comes at a cost. Does poly_wide_int have the same
> wide-int like overflow overloads?
poly_offset_int will be definitely cheaper than other poly_wide_int, it
would need to be at least 66 bits and so 128 bit is certainly cheaper then.
So like this if it passes full bootstrap/regtest?
2025-02-26 Jakub Jelinek <ja...@redhat.com>
PR middle-end/118819
* alias.cc (memrefs_conflict_p): Perform arithmetics on c, xsize and
ysize in poly_offset_int and return -1 if it is not representable in
poly_int64.
--- gcc/alias.cc.jj 2025-01-02 11:23:24.000000000 +0100
+++ gcc/alias.cc 2025-02-26 12:31:52.860341105 +0100
@@ -2535,19 +2535,39 @@ memrefs_conflict_p (poly_int64 xsize, rt
return memrefs_conflict_p (xsize, x1, ysize, y1, c);
if (poly_int_rtx_p (x1, &cx1))
{
+ poly_offset_int co = c;
+ co -= cx1;
if (poly_int_rtx_p (y1, &cy1))
- return memrefs_conflict_p (xsize, x0, ysize, y0,
- c - cx1 + cy1);
+ {
+ co += cy1;
+ if (!co.to_shwi (&c))
+ return -1;
+ return memrefs_conflict_p (xsize, x0, ysize, y0, c);
+ }
+ else if (!co.to_shwi (&c))
+ return -1;
else
- return memrefs_conflict_p (xsize, x0, ysize, y, c - cx1);
+ return memrefs_conflict_p (xsize, x0, ysize, y, c);
}
else if (poly_int_rtx_p (y1, &cy1))
- return memrefs_conflict_p (xsize, x, ysize, y0, c + cy1);
+ {
+ poly_offset_int co = c;
+ co += cy1;
+ if (!co.to_shwi (&c))
+ return -1;
+ return memrefs_conflict_p (xsize, x, ysize, y0, c);
+ }
return -1;
}
else if (poly_int_rtx_p (x1, &cx1))
- return memrefs_conflict_p (xsize, x0, ysize, y, c - cx1);
+ {
+ poly_offset_int co = c;
+ co -= cx1;
+ if (!co.to_shwi (&c))
+ return -1;
+ return memrefs_conflict_p (xsize, x0, ysize, y, c);
+ }
}
else if (GET_CODE (y) == PLUS)
{
@@ -2563,7 +2583,13 @@ memrefs_conflict_p (poly_int64 xsize, rt
poly_int64 cy1;
if (poly_int_rtx_p (y1, &cy1))
- return memrefs_conflict_p (xsize, x, ysize, y0, c + cy1);
+ {
+ poly_offset_int co = c;
+ co += cy1;
+ if (!co.to_shwi (&c))
+ return -1;
+ return memrefs_conflict_p (xsize, x, ysize, y0, c);
+ }
else
return -1;
}
@@ -2616,8 +2642,16 @@ memrefs_conflict_p (poly_int64 xsize, rt
if (maybe_gt (xsize, 0))
xsize = -xsize;
if (maybe_ne (xsize, 0))
- xsize += sc + 1;
- c -= sc + 1;
+ {
+ poly_offset_int xsizeo = xsize;
+ xsizeo += sc + 1;
+ if (!xsizeo.to_shwi (&xsize))
+ return -1;
+ }
+ poly_offset_int co = c;
+ co -= sc + 1;
+ if (!co.to_shwi (&c))
+ return -1;
return memrefs_conflict_p (xsize, canon_rtx (XEXP (x, 0)),
ysize, y, c);
}
@@ -2631,8 +2665,16 @@ memrefs_conflict_p (poly_int64 xsize, rt
if (maybe_gt (ysize, 0))
ysize = -ysize;
if (maybe_ne (ysize, 0))
- ysize += sc + 1;
- c += sc + 1;
+ {
+ poly_offset_int ysizeo = ysize;
+ ysizeo += sc + 1;
+ if (!ysizeo.to_shwi (&ysize))
+ return -1;
+ }
+ poly_offset_int co = c;
+ co += sc + 1;
+ if (!co.to_shwi (&c))
+ return -1;
return memrefs_conflict_p (xsize, x,
ysize, canon_rtx (XEXP (y, 0)), c);
}
@@ -2643,7 +2685,11 @@ memrefs_conflict_p (poly_int64 xsize, rt
poly_int64 cx, cy;
if (poly_int_rtx_p (x, &cx) && poly_int_rtx_p (y, &cy))
{
- c += cy - cx;
+ poly_offset_int co = c;
+ co += cy;
+ co -= cx;
+ if (!co.to_shwi (&c))
+ return -1;
return offset_overlap_p (c, xsize, ysize);
}
Jakub
