Re: Should gcc-4.0 apply mathematical associative rules for addition or multiplication

[Fariborz Jahanian <fjahanian at apple dot com>]

On Oct 4, 2004, at 7:35 PM, Gabriel Dos Reis wrote:
> | associative_tree_code also returns true for MIN_EXPR/MAX_EXPR. I 
> think
> | we want to only
> | exclude PLUS_EXPR/MULT_EXPR.
>
> and all additive expressions (e.g. MINUS_EXPR) and multiplicative
> expressions (include division).
>
> -- Gaby

I am testing the following patch. This patch disallows folding of 
MULT_EXPR/PLUS_EXPR
with floating operands. Only such illegal operations which can happen 
in the fall-thru block of
code.

- fariborz

Index: tree-ssa-dom.c
===================================================================
RCS file: /cvs/gcc/gcc/gcc/tree-ssa-dom.c,v
retrieving revision 2.56
diff -c -p -r2.56 tree-ssa-dom.c
*** tree-ssa-dom.c      29 Sep 2004 02:50:46 -0000      2.56
--- tree-ssa-dom.c      5 Oct 2004 15:04:43 -0000
*************** simplify_rhs_and_lookup_avail_expr (stru
*** 1606,1612 ****
          tree rhs_def_rhs = TREE_OPERAND (rhs_def_stmt, 1);
          enum tree_code rhs_def_code = TREE_CODE (rhs_def_rhs);

!         if (rhs_code == rhs_def_code
              || (rhs_code == PLUS_EXPR && rhs_def_code == MINUS_EXPR)
              || (rhs_code == MINUS_EXPR && rhs_def_code == PLUS_EXPR))
            {
--- 1606,1615 ----
          tree rhs_def_rhs = TREE_OPERAND (rhs_def_stmt, 1);
          enum tree_code rhs_def_code = TREE_CODE (rhs_def_rhs);

!         if ((rhs_code == rhs_def_code
!              && !(!flag_unsafe_math_optimizations
!                   && (rhs_code == MULT_EXPR || rhs_code == PLUS_EXPR)
!                   && FLOAT_TYPE_P (TREE_TYPE (rhs))))
              || (rhs_code == PLUS_EXPR && rhs_def_code == MINUS_EXPR)
              || (rhs_code == MINUS_EXPR && rhs_def_code == PLUS_EXPR))
            {