Re: [PATCH] bitint: Fix up lowering of COMPLEX_EXPR [PR115544]

[Richard Biener <rguenther@suse.de>]

> Am 19.06.2024 um 20:44 schrieb Jakub Jelinek <jakub@redhat.com>:
> 
> Hi!
> 
> We don't really support _Complex _BitInt(N), the only place we use
> bitint complex types is for the .{ADD,SUB,MUL}_OVERFLOW internal function
> results and COMPLEX_EXPR in the usual case should be either not present
> yet because the ifns weren't folded and will be lowered, or optimized
> into something simpler, because normally the complex bitint should be
> used just for extracting the 2 subparts from it.
> Still, with disabled optimizations it can occassionally happen that it
> appears in the IL and that is why there is support for lowering those,
> but it doesn't handle optimizing those too much, so if it uses SSA_NAME,
> it relies on them having a backing VAR_DECL during the lowering.
> This is normally achieves through the
>                      && ((is_gimple_assign (use_stmt)
>                           && (gimple_assign_rhs_code (use_stmt)
>                               != COMPLEX_EXPR))
>                          || gimple_code (use_stmt) == GIMPLE_COND)
> hunk in gimple_lower_bitint, but as the following testcase shows, there
> is one thing I've missed, the load optimization isn't guarded by the
> above stuff.  So, either we'd need to add support for loads to
> lower_complexexpr_stmt, or because they should be really rare, this
> patch just disables the load optimization if at least one load use is
> a COMPLEX_EXPR (like we do already for PHIs, calls, asm).

Sounds reasonable.

> Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?

Ok

Richard 

> 2024-06-19  Jakub Jelinek  <jakub@redhat.com>
> 
>    PR tree-optimization/115544
>    * gimple-lower-bitint.cc (gimple_lower_bitint): Disable optimizing
>    loads used by COMPLEX_EXPR operands.
> 
>    * gcc.dg/bitint-107.c: New test.
> 
> --- gcc/gimple-lower-bitint.cc.jj    2024-06-07 12:17:09.811966904 +0200
> +++ gcc/gimple-lower-bitint.cc    2024-06-19 15:27:22.378759911 +0200
> @@ -6630,7 +6630,10 @@ gimple_lower_bitint (void)
>            continue;
>          if (gimple_code (use_stmt) == GIMPLE_PHI
>              || is_gimple_call (use_stmt)
> -              || gimple_code (use_stmt) == GIMPLE_ASM)
> +              || gimple_code (use_stmt) == GIMPLE_ASM
> +              || (is_gimple_assign (use_stmt)
> +              && (gimple_assign_rhs_code (use_stmt)
> +                  == COMPLEX_EXPR)))
>            {
>              optimizable_load = false;
>              break;
> --- gcc/testsuite/gcc.dg/bitint-107.c.jj    2024-06-19 15:36:32.817747449 +0200
> +++ gcc/testsuite/gcc.dg/bitint-107.c    2024-06-19 14:03:31.383805280 +0200
> @@ -0,0 +1,16 @@
> +/* PR tree-optimization/115544 */
> +/* { dg-do compile { target bitint } } */
> +/* { dg-options "-O -fno-tree-fre -fno-tree-ccp -fno-tree-forwprop" } */
> +
> +#if __BITINT_MAXWIDTH__ >= 129
> +typedef _BitInt(129) B;
> +#else
> +typedef _BitInt(63) B;
> +#endif
> +B a, b;
> +
> +int
> +foo (void)
> +{
> +  return __builtin_mul_overflow (a, 1, &b);
> +}
> 
>    Jakub
>