On Mon, 2 Nov 2015, Jan Hubicka wrote:
> Hi,
> this patch adds OEP_MATCH_SIDE_EFFECT to tell operand_equal_p that the two
> operands compared are from different code paths and thus they can be matched
> even if they have side effects.
>
> I.e.
>
> volatile int a;
>
> if (a==a)
>
> has two reads and thus can't be optimized (I guess), while
>
> b?a:a
>
> can be optimized. OEP_MATCH_SIDE_EFFECTS will be needed by ipa-icf. I
> changed
> gimple_operand_equal_value_p in tail-merge to use it. I do not know how to
> make the folding of ?: happen, since there seems to be no way to specify flags
> to match_operand in match.pd. This makes it hard to construct a testcase - all
> my attempts to trick tree-ssa-tailmerge to merge something that involve
> volatile
> operands failed, because it uses GVN to compare and GVN punt on these.
>
> I also wonder if we can drop OEP_CONSTANT_ADDRESS_OF. The only difference is
> that
> OEP_MATCH_SIDE_EFFECTS permits function calls. I think those should not
> appear
> in constant addresses.
But you don't even need the call case for tailmerge or ICF as we don't
have CALL_EXPRs in GIMPLE. No?
And you mean the difference of OEP_CONSTANT_ADDRESS_OF to
OEP_ADDRESS_OF | OEP_MATCH_SIDE_EFFECTS then, right?
Ok if you go forward with that and do not change the CALL_EXPR case
for now (you may add a FIXME comment).
Thanks,
Richard.
> Bootstrapped/regtested x86_64-linux, OK?
>
> * tree-core.h (OEP_MATCH_SIDE_EFFECTS): New.
> * tree-ssa-tail-merge.c (gimple_operand_equal_value_p): Pass
> OEP_MATCH_SIDE_EFFECTS
> * fold-const.c (operand_equal_p): Support OEP_MATCH_SIDE_EFFECTS.
> Index: tree-core.h
> ===================================================================
> --- tree-core.h (revision 229263)
> +++ tree-core.h (working copy)
> @@ -732,7 +732,8 @@ enum operand_equal_flag {
> OEP_ONLY_CONST = 1,
> OEP_PURE_SAME = 2,
> OEP_CONSTANT_ADDRESS_OF = 4,
> - OEP_ADDRESS_OF = 8
> + OEP_ADDRESS_OF = 8,
> + OEP_MATCH_SIDE_EFFECTS = 16
> };
>
> /* Enum and arrays used for tree allocation stats.
> Index: tree-ssa-tail-merge.c
> ===================================================================
> --- tree-ssa-tail-merge.c (revision 229263)
> +++ tree-ssa-tail-merge.c (working copy)
> @@ -1091,7 +1091,7 @@ gimple_operand_equal_value_p (tree t1, t
> || t2 == NULL_TREE)
> return false;
>
> - if (operand_equal_p (t1, t2, 0))
> + if (operand_equal_p (t1, t2, OEP_MATCH_SIDE_EFFECTS))
> return true;
>
> return gvn_uses_equal (t1, t2);
> Index: fold-const.c
> ===================================================================
> --- fold-const.c (revision 229494)
> +++ fold-const.c (working copy)
> @@ -2657,8 +2657,7 @@ combine_comparisons (location_t loc,
> }
>
> /* Return nonzero if two operands (typically of the same tree node)
> - are necessarily equal. If either argument has side-effects this
> - function returns zero. FLAGS modifies behavior as follows:
> + are necessarily equal. FLAGS modifies behavior as follows:
>
> If OEP_ONLY_CONST is set, only return nonzero for constants.
> This function tests whether the operands are indistinguishable;
> @@ -2685,7 +2684,12 @@ combine_comparisons (location_t loc,
> If OEP_ADDRESS_OF is set, we are actually comparing addresses of objects,
> not values of expressions. OEP_CONSTANT_ADDRESS_OF in addition to
> OEP_ADDRESS_OF is used for ADDR_EXPR with TREE_CONSTANT flag set and we
> - further ignore any side effects on SAVE_EXPRs then. */
> + further ignore any side effects on SAVE_EXPRs then.
> +
> + Unless OEP_MATCH_SIDE_EFFECTS is set, the function returns false on
> + any operand with side effect. This is unnecesarily conservative in the
> + case we know that arg0 and arg1 are in disjoint code paths (such as in
> + ?: operator). */
>
> int
> operand_equal_p (const_tree arg0, const_tree arg1, unsigned int flags)
> @@ -2814,7 +2818,7 @@ operand_equal_p (const_tree arg0, const_
> they are necessarily equal as well. */
> if (arg0 == arg1 && ! (flags & OEP_ONLY_CONST)
> && (TREE_CODE (arg0) == SAVE_EXPR
> - || (flags & OEP_CONSTANT_ADDRESS_OF)
> + || (flags & (OEP_CONSTANT_ADDRESS_OF | OEP_MATCH_SIDE_EFFECTS))
> || (! TREE_SIDE_EFFECTS (arg0) && ! TREE_SIDE_EFFECTS (arg1))))
> return 1;
>
> @@ -2936,7 +2940,7 @@ operand_equal_p (const_tree arg0, const_
> /* If either of the pointer (or reference) expressions we are
> dereferencing contain a side effect, these cannot be equal,
> but their addresses can be. */
> - if ((flags & OEP_CONSTANT_ADDRESS_OF) == 0
> + if ((flags & (OEP_CONSTANT_ADDRESS_OF | OEP_MATCH_SIDE_EFFECTS)) == 0
> && (TREE_SIDE_EFFECTS (arg0)
> || TREE_SIDE_EFFECTS (arg1)))
> return 0;
> @@ -3097,15 +3101,16 @@ operand_equal_p (const_tree arg0, const_
> return 0;
> }
>
> - {
> - unsigned int cef = call_expr_flags (arg0);
> - if (flags & OEP_PURE_SAME)
> - cef &= ECF_CONST | ECF_PURE;
> - else
> - cef &= ECF_CONST;
> - if (!cef)
> - return 0;
> - }
> + if (!(flags & OEP_MATCH_SIDE_EFFECTS))
> + {
> + unsigned int cef = call_expr_flags (arg0);
> + if (flags & OEP_PURE_SAME)
> + cef &= ECF_CONST | ECF_PURE;
> + else
> + cef &= ECF_CONST;
> + if (!cef)
> + return 0;
> + }
>
> /* Now see if all the arguments are the same. */
> {
>
>
--
Richard Biener <rguent...@suse.de>
SUSE LINUX GmbH, GF: Felix Imendoerffer, Jane Smithard, Graham Norton, HRB
21284 (AG Nuernberg)
