Re: Fixes for PR66178

[Jeff Law <law at redhat dot com>]

On 01/20/2016 07:25 AM, Bernd Schmidt wrote:
> PR66178 has some testcases where we construct expressions involving
> additions and subtractions of label addresses, and we crash when trying
> to expand these. There are two different issues here, shown by various
> testcases in the PR:
>
>   * expand_expr_real_2 can drop EXPAND_INITIALIZER and then go into
>     a path where it wants to gen_reg_rtx.
>   * simplify-rtx can turn subtractions into NOT operations in some
>     cases. That seems inadvisable for symbolic expressions.
>
> The following was bootstrapped and tested on x86_64-linux. Ok for all
> branches?
>
>      PR middle-end/66178
>      * expr.c (expand_expr_real_2) [PLUS_EXPR, MINUS_EXPR]: Don't
>      drop EXPAND_INITIALIZER.
>      * rtl.h (contains_symbolic_reference_p): Declare.
>      * rtlanal.c (contains_symbolic_reference_p): New function.
>      * simplify-rtx.c (simplify_binary_operation_1): Don't turn
>      a subtraction into a NOT if symbolic constants are involved.
>
> testsuite/
>      PR middle-end/66178
>      gcc.dg/torture/pr66178.c: New test.
>
> pr66178.diff
>
>
>
> Index: gcc/rtlanal.c
> ===================================================================
> --- gcc/rtlanal.c	(revision 232555)
> +++ gcc/rtlanal.c	(working copy)
> @@ -6243,6 +6243,19 @@ contains_symbol_ref_p (const_rtx x)
>     return false;
>   }
>
> +/* Return true if RTL X contains a SYMBOL_REF or LABEL_REF.  */
> +
> +bool
> +contains_symbolic_reference_p (const_rtx x)
> +{
> +  subrtx_iterator::array_type array;
> +  FOR_EACH_SUBRTX (iter, array, x, ALL)
> +    if (SYMBOL_REF_P (*iter) || GET_CODE (*iter) == LABEL_REF)
> +      return true;
> +
> +  return false;
> +}
> +
I thought we already had a routine to do this.  I thought we needed it 
in varasm.c, but couldn't find it.  Then I found contains_symbol_ref_p, 
but obviously that's not good enough because you need LABEL_REFs too.


>   /* Return true if X contains a thread-local symbol.  */
>
>   bool
> Index: gcc/simplify-rtx.c
> ===================================================================
> --- gcc/simplify-rtx.c	(revision 232555)
> +++ gcc/simplify-rtx.c	(working copy)
> @@ -2277,8 +2277,11 @@ simplify_binary_operation_1 (enum rtx_co
>         if (!HONOR_SIGNED_ZEROS (mode) && trueop0 == CONST0_RTX (mode))
>   	return simplify_gen_unary (NEG, mode, op1, mode);
>
> -      /* (-1 - a) is ~a.  */
> -      if (trueop0 == constm1_rtx)
> +      /* (-1 - a) is ~a, unless the expression avoids symbolic constants,
> +	 in which case not retaining additions and subtractions could
> +	 cause invalid assembly to be produced.  */
"avoids?" Somehow this isn't parsing well.

"unless the expression has symbolic constants" or something similar is 
what I think you want.

OK with the comment fixed.

jeff