Re: [PATCH] bitint: Avoid rewriting large/huge _BitInt vars into SSA after bitint lowering [PR114278]

[Richard Biener <rguenther@suse.de>]

> Am 09.03.2024 um 09:28 schrieb Jakub Jelinek <jakub@redhat.com>:
> 
> Hi!
> 
> The following testcase ICEs, because update-address-taken subpass of
> fre5 rewrites
>  _BitInt(128) b;
>  vector(16) unsigned char _3;
> 
>  <bb 2> [local count: 1073741824]:
>  _3 = MEM <vector(16) unsigned char> [(char * {ref-all})p_2(D)];
>  MEM <vector(16) unsigned char> [(char * {ref-all})&b] = _3;
>  b ={v} {CLOBBER(eos)};
> to
>  _BitInt(128) b;
>  vector(16) unsigned char _3;
> 
>  <bb 2> [local count: 1073741824]:
>  _3 = MEM <vector(16) unsigned char> [(char * {ref-all})p_2(D)];
>  b_5 = VIEW_CONVERT_EXPR<_BitInt(128)>(_3);
> but we can't have large/huge _BitInt vars in SSA form after the bitint
> lowering except for function arguments loaded from memory, as expansion
> isn't able to deal with those, it relies on bitint lowering to lower
> those operations.
> The following patch fixes that by not clearing TREE_ADDRESSABLE for
> large/huge _BitInt vars after bitint lowering, such that we don't
> rewrite them into SSA form.
> 
> Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?
> 

Ideally we’d clear TREE_ADDRESSABLE but set DECL_NOT_GIMPLE_REG, I think the analysis where we check the base would be a more appropriate place to enforce that.

Richard 

> 2024-03-09  Jakub Jelinek  <jakub@redhat.com>
> 
>    PR tree-optimization/114278
>    * tree-ssa.cc (maybe_optimize_var): Punt on large/huge _BitInt
>    vars after bitint lowering.
> 
>    * gcc.dg/bitint-99.c: New test.
> 
> --- gcc/tree-ssa.cc.jj    2024-01-03 11:51:39.902615009 +0100
> +++ gcc/tree-ssa.cc    2024-03-08 14:24:11.844821915 +0100
> @@ -1753,7 +1753,11 @@ maybe_optimize_var (tree var, bitmap add
>   /* Global Variables, result decls cannot be changed.  */
>   if (is_global_var (var)
>       || TREE_CODE (var) == RESULT_DECL
> -      || bitmap_bit_p (addresses_taken, DECL_UID (var)))
> +      || bitmap_bit_p (addresses_taken, DECL_UID (var))
> +      || (TREE_CODE (TREE_TYPE (var)) == BITINT_TYPE
> +      /* Don't change large/huge _BitInt vars after _BitInt lowering.  */
> +      && (cfun->curr_properties & PROP_gimple_lbitint) != 0
> +      && TYPE_PRECISION (TREE_TYPE (var)) > MAX_FIXED_MODE_SIZE))
>     return;
> 
>   bool maybe_reg = false;
> --- gcc/testsuite/gcc.dg/bitint-99.c.jj    2024-03-08 14:26:17.658069942 +0100
> +++ gcc/testsuite/gcc.dg/bitint-99.c    2024-03-08 14:25:36.292645965 +0100
> @@ -0,0 +1,26 @@
> +/* PR tree-optimization/114278 */
> +/* { dg-do compile { target bitint } } */
> +/* { dg-options "-O2 -fno-tree-dce -fno-tree-dse -fno-tree-ccp" } */
> +/* { dg-additional-options "-mavx2" { target i?86-*-* x86_64-*-* } } */
> +
> +void
> +foo (void *p)
> +{
> +  _BitInt(64) b = *(_BitInt(64) *) __builtin_memmove (&b, p, sizeof (_BitInt(64)));
> +}
> +
> +#if __BITINT_MAXWIDTH__ >= 128
> +void
> +bar (void *p)
> +{
> +  _BitInt(128) b = *(_BitInt(128) *) __builtin_memmove (&b, p, sizeof (_BitInt(128)));
> +}
> +#endif
> +
> +#if __BITINT_MAXWIDTH__ >= 256
> +void
> +baz (void *p)
> +{
> +  _BitInt(256) b = *(_BitInt(256) *) __builtin_memmove (&b, p, sizeof (_BitInt(256)));
> +}
> +#endif
> 
>    Jakub
>