On Wed, 28 Jul 2021, Jakub Jelinek wrote:
> Hi!
>
> The following testcase ICEs. The problem is that for __builtin_bswap16
> (and only that, others are fine) the argument of the builtin is promoted
> to int while the patterns assume it is not and is the same as that of
> the return type.
> For the bswap simplifications before these new ones it just means we
> fail to optimize stuff like __builtin_bswap16 (__builtin_bswap16 (x))
> because there are casts in between, but the last one, equality comparison
> of __builtin_bswap16 with integer constant results in ICE, because
> we create comparison with incompatible types of the operands, and the
> other might be fine because usually we bit and the operand before promoting,
> but I think it is too dangerous to rely on it, one day we find out that
> because it is operand to such a built in, we can throw away any changes
> that affect the upper bits and all of sudden it would misbehave.
>
> So, this patch introduces converts that shouldn't do anything for
> bswap{32,64,128} and should fix these issues for bswap16.
>
> Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?
OK.
Richard.
> 2021-07-28 Jakub Jelinek <ja...@redhat.com>
>
> PR middle-end/101642
> * match.pd (bswap16 (x) == bswap16 (y)): Cast both operands
> to type of bswap16 for comparison.
> (bswap16 (x) == cst): Cast bswap16 operand to type of cst.
>
> * gcc.c-torture/compile/pr101642.c: New test.
>
> --- gcc/match.pd.jj 2021-07-27 09:47:44.000000000 +0200
> +++ gcc/match.pd 2021-07-27 16:16:19.867757153 +0200
> @@ -3641,11 +3641,13 @@ (define_operator_list COND_TERNARY
> (bitop @0 (bswap @1))))
> (for cmp (eq ne)
> (simplify
> - (cmp (bswap @0) (bswap @1))
> - (cmp @0 @1))
> + (cmp (bswap@2 @0) (bswap @1))
> + (with { tree ctype = TREE_TYPE (@2); }
> + (cmp (convert:ctype @0) (convert:ctype @1))))
> (simplify
> (cmp (bswap @0) INTEGER_CST@1)
> - (cmp @0 (bswap @1))))
> + (with { tree ctype = TREE_TYPE (@1); }
> + (cmp (convert:ctype @0) (bswap @1)))))
> /* (bswap(x) >> C1) & C2 can sometimes be simplified to (x >> C3) & C2. */
> (simplify
> (bit_and (convert1? (rshift@0 (convert2? (bswap@4 @1)) INTEGER_CST@2))
> --- gcc/testsuite/gcc.c-torture/compile/pr101642.c.jj 2021-07-27
> 16:34:44.910039793 +0200
> +++ gcc/testsuite/gcc.c-torture/compile/pr101642.c 2021-07-27
> 16:32:24.661907592 +0200
> @@ -0,0 +1,17 @@
> +/* PR middle-end/101642 */
> +
> +int x;
> +
> +unsigned short
> +foo (void)
> +{
> + return __builtin_bswap16 (x) ? : 0;
> +}
> +
> +int
> +bar (int x, int y)
> +{
> + unsigned short a = __builtin_bswap16 ((unsigned short) x);
> + unsigned short b = __builtin_bswap16 ((unsigned short) y);
> + return a == b;
> +}
>
> Jakub
>
>
--
Richard Biener <rguent...@suse.de>
SUSE Software Solutions Germany GmbH, Maxfeldstrasse 5, 90409 Nuernberg,
Germany; GF: Felix Imendörffer; HRB 36809 (AG Nuernberg)
