[PATCH] Avoid creating overflows in match.pd (P + A) - (P + B) POINTER_DIFF_EXPR optimization (PR c/61240)
Richard Biener
rguenther@suse.de
Thu Jan 18 08:15:00 GMT 2018
On Wed, 17 Jan 2018, Jakub Jelinek wrote:
> Hi!
>
> POINTER_DIFF_EXPR returns a signed integer, but sadly POINTER_PLUS_EXPR
> second arguments are unsigned integers, so if we are adding negative numbers
> to pointers, those are very large numbers and we get TREE_OVERFLOW which the
> C FE then during c_fully_fold diagnoses.
Bah...
> We want to treat the numbers as signed integers for this purpose, using
> VCE seems easiest way to get rid of the unwanted overflows.
>
> Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?
>
> Or do you prefer manual fold_converts in the (with { }) block + test
> for INTEGER_CST && TREE_OVERFLOW + drop_tree_overflow instead?
I think the patch is ok as-is. I really hope to make the
POINTER_PLUS_EXPR offset operand signed in next stage1.
Thanks,
Richard.
> 2018-01-17 Jakub Jelinek <jakub@redhat.com>
>
> PR c/61240
> * match.pd ((P + A) - P, P - (P + A), (P + A) - (P + B)): For
> pointer_diff optimizations use view_convert instead of convert.
>
> * gcc.dg/pr61240.c: New test.
>
> --- gcc/match.pd.jj 2018-01-15 10:02:04.000000000 +0100
> +++ gcc/match.pd 2018-01-17 17:10:54.855061485 +0100
> @@ -1832,7 +1832,10 @@ DEFINE_INT_AND_FLOAT_ROUND_FN (RINT)
> /* The second argument of pointer_plus must be interpreted as signed, and
> thus sign-extended if necessary. */
> (with { tree stype = signed_type_for (TREE_TYPE (@1)); }
> - (convert (convert:stype @1))))
> + /* Use view_convert instead of convert here, as POINTER_PLUS_EXPR
> + second arg is unsigned even when we need to consider it as signed,
> + we don't want to diagnose overflow here. */
> + (convert (view_convert:stype @1))))
>
> /* (T)P - (T)(P + A) -> -(T) A */
> (simplify
> @@ -1876,7 +1879,10 @@ DEFINE_INT_AND_FLOAT_ROUND_FN (RINT)
> /* The second argument of pointer_plus must be interpreted as signed, and
> thus sign-extended if necessary. */
> (with { tree stype = signed_type_for (TREE_TYPE (@1)); }
> - (negate (convert (convert:stype @1)))))
> + /* Use view_convert instead of convert here, as POINTER_PLUS_EXPR
> + second arg is unsigned even when we need to consider it as signed,
> + we don't want to diagnose overflow here. */
> + (negate (convert (view_convert:stype @1)))))
>
> /* (T)(P + A) - (T)(P + B) -> (T)A - (T)B */
> (simplify
> @@ -1927,7 +1933,11 @@ DEFINE_INT_AND_FLOAT_ROUND_FN (RINT)
> /* The second argument of pointer_plus must be interpreted as signed, and
> thus sign-extended if necessary. */
> (with { tree stype = signed_type_for (TREE_TYPE (@1)); }
> - (minus (convert (convert:stype @1)) (convert (convert:stype @2)))))))
> + /* Use view_convert instead of convert here, as POINTER_PLUS_EXPR
> + second arg is unsigned even when we need to consider it as signed,
> + we don't want to diagnose overflow here. */
> + (minus (convert (view_convert:stype @1))
> + (convert (view_convert:stype @2)))))))
>
>
> /* Simplifications of MIN_EXPR, MAX_EXPR, fmin() and fmax(). */
> --- gcc/testsuite/gcc.dg/pr61240.c.jj 2018-01-17 17:25:45.821030898 +0100
> +++ gcc/testsuite/gcc.dg/pr61240.c 2018-01-17 17:26:24.118029550 +0100
> @@ -0,0 +1,20 @@
> +/* PR c/61240 */
> +/* { dg-do compile } */
> +
> +typedef __PTRDIFF_TYPE__ ptrdiff_t;
> +
> +ptrdiff_t
> +foo (ptrdiff_t a[4])
> +{
> + int i[4];
> + int *p = i + 2;
> + static ptrdiff_t b = p - (p - 1); /* { dg-bogus "integer overflow in expression" } */
> + static ptrdiff_t c = (p - 1) - p; /* { dg-bogus "integer overflow in expression" } */
> + static ptrdiff_t d = (p - 2) - (p - 1);/* { dg-bogus "integer overflow in expression" } */
> + static ptrdiff_t e = (p - 1) - (p - 2);/* { dg-bogus "integer overflow in expression" } */
> + a[0] = p - (p - 1); /* { dg-bogus "integer overflow in expression" } */
> + a[1] = (p - 1) - p; /* { dg-bogus "integer overflow in expression" } */
> + a[2] = (p - 2) - (p - 1); /* { dg-bogus "integer overflow in expression" } */
> + a[3] = (p - 1) - (p - 2); /* { dg-bogus "integer overflow in expression" } */
> + return b + c + d + e;
> +}
>
> Jakub
>
>
--
Richard Biener <rguenther@suse.de>
SUSE LINUX GmbH, GF: Felix Imendoerffer, Jane Smithard, Graham Norton, HRB 21284 (AG Nuernberg)
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