Move "X +- C1 CMP C2 to X CMP C2 -+ C1" to match.pd
Richard Biener
richard.guenther@gmail.com
Wed Apr 27 12:02:00 GMT 2016
On Wed, Apr 27, 2016 at 7:34 AM, Marc Glisse <marc.glisse@inria.fr> wrote:
> Here is the current patch (passed regtest), after moving defer/undefer from
> forwprop to fold_stmt_1. I am not sure if checking no_warning at the end of
> fold_stmt_1 is safe, or if I should save its value at the beginning of the
> function, in case some of the transformations clear it.
I think you need to check it on the original stmt, it is preserved only
if we re-use the old stmt memory.
>
> On Tue, 26 Apr 2016, Marc Glisse wrote:
>
>> On Tue, 26 Apr 2016, Richard Biener wrote:
>>
>>> On Sun, Apr 24, 2016 at 7:14 PM, Marc Glisse <marc.glisse@inria.fr>
>>> wrote:
>>>>
>>>> Hello,
>>>>
>>>> trying to move a first pattern from fold_comparison.
>>>>
>>>> I first tried without single_use. It brought the number of 'free' in
>>>> g++.dg/tree-ssa/pr61034.C down to 11, changed gcc.dg/sms-6.c to only 2
>>>> SMS
>>>> (I don't think the generated code was worse, maybe even better, but I
>>>> don't
>>>> know ppc asm), broke Wstrict-overflow-18.c (the optimization moved from
>>>> VRP
>>>> to CCP if I remember correctly), and caused IVOPTS to make a mess in
>>>> guality/pr54693-2.c (much longer code, and many <optimized> debug
>>>> variables). If someone wants to drop the single_use, they can work on
>>>> that
>>>> after this patch is in.
>>>>
>>>> The conditions do not exactly match the ones in fold-const.c, but I
>>>> guess
>>>> they are close. The warning in the constant case was missing in
>>>> fold_comparison, but present in VRP, so I had to add it not to regress.
>>>>
>>>> I don't think we were warning much from match.pd. I can't say that I am
>>>> a
>>>> big fan of those strict overflow warnings, but I expect people would
>>>> complain if we just dropped the existing ones when moving the transforms
>>>> to
>>>> match.pd?
>>>
>>>
>>> I just dropped them for patterns I moved (luckily we didn't have
>>> testcases sofar ;))
>>>
>>> If we really want to warn from match.pd then you should do the
>>> defer/undefer
>>> stuff in fold_stmt itself (same condition I guess) and defer/undefer
>>> without
>>> warning in gimple_fold_stmt_to_constant_1.
>>
>>
>> Moving it to fold_stmt_1 seems like a good idea, much better than putting
>> it in forwprop. Looking at gimple_fold_stmt_to_constant_1 on the other hand,
>> I have some concerns. If we do not warn for gimple_fold_stmt_to_constant_1,
>> we are going to miss some warnings (I believe there is at least one testcase
>> that will break, where VRP currently warns but CCP will come first). On the
>> other hand, gimple_fold_stmt_to_constant_1 doesn't do much validation on its
>> return value, each caller has their own idea of which results are
>> acceptable, so it is only in the (many) callers that we can defer/undefer,
>> or we might warn for transformations that we don't actually perform. CCP
>> already has the defer/undefer calls around ccp_fold and thus
>> gimple_fold_stmt_to_constant_1.
>>
>>> So you actually ran into a testcase that expected the warning?
>>
>>
>> Several of them if I remember correctly...
>>
>>>> I wanted to restrict the equality case to TYPE_OVERFLOW_WRAPS ||
>>>> TYPE_OVERFLOW_UNDEFINED, but that broke 20041114-1.c at -O1 (no strict
>>>> overflow), so I went with some kind of complement we use elsewhere.
>>>
>>>
>>> I think I prefer to move things 1:1 (unless sth regresses) and fix bugs
>>> in the
>>> fold-const.c variant as followup (possibly also adding testcases).
>>
>>
>> Well, yes, but things do indeed regress quite regularly when moving things
>> 1:1 :-( At least unless we add a big (if (GENERIC) ...) around the
>> transformation.
>>
>>> IMHO -fno-strict-overflow needs to go. It has very wary designed
>>> semantics
>>> (ops neither wrap nor have undefined overflow).
>>
>>
>> Maybe make it an alias for -fwrapv?
>
>
> --
> Marc Glisse
>
> Index: trunk4/gcc/fold-const.c
> ===================================================================
> --- trunk4/gcc/fold-const.c (revision 235452)
> +++ trunk4/gcc/fold-const.c (working copy)
> @@ -290,21 +290,21 @@ fold_undefer_and_ignore_overflow_warning
>
> bool
> fold_deferring_overflow_warnings_p (void)
> {
> return fold_deferring_overflow_warnings > 0;
> }
>
> /* This is called when we fold something based on the fact that signed
> overflow is undefined. */
>
> -static void
> +void
> fold_overflow_warning (const char* gmsgid, enum warn_strict_overflow_code
> wc)
> {
> if (fold_deferring_overflow_warnings > 0)
> {
> if (fold_deferred_overflow_warning == NULL
> || wc < fold_deferred_overflow_code)
> {
> fold_deferred_overflow_warning = gmsgid;
> fold_deferred_overflow_code = wc;
> }
> @@ -8366,89 +8366,20 @@ fold_comparison (location_t loc, enum tr
> {
> const bool equality_code = (code == EQ_EXPR || code == NE_EXPR);
> tree arg0, arg1, tem;
>
> arg0 = op0;
> arg1 = op1;
>
> STRIP_SIGN_NOPS (arg0);
> STRIP_SIGN_NOPS (arg1);
>
> - /* Transform comparisons of the form X +- C1 CMP C2 to X CMP C2 -+ C1.
> */
> - if ((TREE_CODE (arg0) == PLUS_EXPR || TREE_CODE (arg0) == MINUS_EXPR)
> - && (equality_code
> - || (ANY_INTEGRAL_TYPE_P (TREE_TYPE (arg0))
> - && TYPE_OVERFLOW_UNDEFINED (TREE_TYPE (arg0))))
> - && TREE_CODE (TREE_OPERAND (arg0, 1)) == INTEGER_CST
> - && !TREE_OVERFLOW (TREE_OPERAND (arg0, 1))
> - && TREE_CODE (arg1) == INTEGER_CST
> - && !TREE_OVERFLOW (arg1))
> - {
> - const enum tree_code
> - reverse_op = TREE_CODE (arg0) == PLUS_EXPR ? MINUS_EXPR : PLUS_EXPR;
> - tree const1 = TREE_OPERAND (arg0, 1);
> - tree const2 = fold_convert_loc (loc, TREE_TYPE (const1), arg1);
> - tree variable = TREE_OPERAND (arg0, 0);
> - tree new_const = int_const_binop (reverse_op, const2, const1);
> -
> - /* If the constant operation overflowed this can be
> - simplified as a comparison against INT_MAX/INT_MIN. */
> - if (TREE_OVERFLOW (new_const)
> - && !TYPE_OVERFLOW_WRAPS (TREE_TYPE (arg0)))
> - {
> - int const1_sgn = tree_int_cst_sgn (const1);
> - enum tree_code code2 = code;
> -
> - /* Get the sign of the constant on the lhs if the
> - operation were VARIABLE + CONST1. */
> - if (TREE_CODE (arg0) == MINUS_EXPR)
> - const1_sgn = -const1_sgn;
> -
> - /* The sign of the constant determines if we overflowed
> - INT_MAX (const1_sgn == -1) or INT_MIN (const1_sgn == 1).
> - Canonicalize to the INT_MIN overflow by swapping the comparison
> - if necessary. */
> - if (const1_sgn == -1)
> - code2 = swap_tree_comparison (code);
> -
> - /* We now can look at the canonicalized case
> - VARIABLE + 1 CODE2 INT_MIN
> - and decide on the result. */
> - switch (code2)
> - {
> - case EQ_EXPR:
> - case LT_EXPR:
> - case LE_EXPR:
> - return
> - omit_one_operand_loc (loc, type, boolean_false_node,
> variable);
> -
> - case NE_EXPR:
> - case GE_EXPR:
> - case GT_EXPR:
> - return
> - omit_one_operand_loc (loc, type, boolean_true_node,
> variable);
> -
> - default:
> - gcc_unreachable ();
> - }
> - }
> - else
> - {
> - if (!equality_code)
> - fold_overflow_warning ("assuming signed overflow does not occur
> "
> - "when changing X +- C1 cmp C2 to "
> - "X cmp C2 -+ C1",
> - WARN_STRICT_OVERFLOW_COMPARISON);
> - return fold_build2_loc (loc, code, type, variable, new_const);
> - }
> - }
> -
> /* For comparisons of pointers we can decompose it to a compile time
> comparison of the base objects and the offsets into the object.
> This requires at least one operand being an ADDR_EXPR or a
> POINTER_PLUS_EXPR to do more than the operand_equal_p test below. */
> if (POINTER_TYPE_P (TREE_TYPE (arg0))
> && (TREE_CODE (arg0) == ADDR_EXPR
> || TREE_CODE (arg1) == ADDR_EXPR
> || TREE_CODE (arg0) == POINTER_PLUS_EXPR
> || TREE_CODE (arg1) == POINTER_PLUS_EXPR))
> {
> Index: trunk4/gcc/fold-const.h
> ===================================================================
> --- trunk4/gcc/fold-const.h (revision 235452)
> +++ trunk4/gcc/fold-const.h (working copy)
> @@ -13,20 +13,22 @@ WARRANTY; without even the implied warra
> FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
> for more details.
>
> You should have received a copy of the GNU General Public License
> along with GCC; see the file COPYING3. If not see
> <http://www.gnu.org/licenses/>. */
>
> #ifndef GCC_FOLD_CONST_H
> #define GCC_FOLD_CONST_H
>
> +#include <flag-types.h>
> +
I think the canonical way is to include options.h where you include
fold-const.h ...
(ick)
Doesn't the prototype serve as a forward declaration only and thus including
options.h from gimple-match-head.c is enough?
Otherwise the patch looks ok to me.
Thanks,
Richard.
> /* Non-zero if we are folding constants inside an initializer; zero
> otherwise. */
> extern int folding_initializer;
>
> /* Convert between trees and native memory representation. */
> extern int native_encode_expr (const_tree, unsigned char *, int, int off =
> -1);
> extern tree native_interpret_expr (tree, const unsigned char *, int);
>
> /* Fold constants as much as possible in an expression.
> Returns the simplified expression.
> @@ -79,20 +81,21 @@ extern bool fold_convertible_p (const_tr
> fold_convert_loc (UNKNOWN_LOCATION, T1, T2)
> extern tree fold_convert_loc (location_t, tree, tree);
> extern tree fold_single_bit_test (location_t, enum tree_code, tree, tree,
> tree);
> extern tree fold_ignored_result (tree);
> extern tree fold_abs_const (tree, tree);
> extern tree fold_indirect_ref_1 (location_t, tree, tree);
> extern void fold_defer_overflow_warnings (void);
> extern void fold_undefer_overflow_warnings (bool, const gimple *, int);
> extern void fold_undefer_and_ignore_overflow_warnings (void);
> extern bool fold_deferring_overflow_warnings_p (void);
> +extern void fold_overflow_warning (const char*, enum
> warn_strict_overflow_code);
> extern int operand_equal_p (const_tree, const_tree, unsigned int);
> extern int multiple_of_p (tree, const_tree, const_tree);
> #define omit_one_operand(T1,T2,T3)\
> omit_one_operand_loc (UNKNOWN_LOCATION, T1, T2, T3)
> extern tree omit_one_operand_loc (location_t, tree, tree, tree);
> #define omit_two_operands(T1,T2,T3,T4)\
> omit_two_operands_loc (UNKNOWN_LOCATION, T1, T2, T3, T4)
> extern tree omit_two_operands_loc (location_t, tree, tree, tree, tree);
> #define invert_truthvalue(T)\
> invert_truthvalue_loc (UNKNOWN_LOCATION, T)
> Index: trunk4/gcc/gimple-fold.c
> ===================================================================
> --- trunk4/gcc/gimple-fold.c (revision 235452)
> +++ trunk4/gcc/gimple-fold.c (working copy)
> @@ -3519,20 +3519,21 @@ maybe_canonicalize_mem_ref_addr (tree *t
>
> /* Worker for both fold_stmt and fold_stmt_inplace. The INPLACE argument
> distinguishes both cases. */
>
> static bool
> fold_stmt_1 (gimple_stmt_iterator *gsi, bool inplace, tree (*valueize)
> (tree))
> {
> bool changed = false;
> gimple *stmt = gsi_stmt (*gsi);
> unsigned i;
> + fold_defer_overflow_warnings ();
>
> /* First do required canonicalization of [TARGET_]MEM_REF addresses
> after propagation.
> ??? This shouldn't be done in generic folding but in the
> propagation helpers which also know whether an address was
> propagated.
> Also canonicalize operand order. */
> switch (gimple_code (stmt))
> {
> case GIMPLE_ASSIGN:
> @@ -3811,20 +3812,22 @@ fold_stmt_1 (gimple_stmt_iterator *gsi,
> {
> tree new_lhs = maybe_fold_reference (lhs, true);
> if (new_lhs)
> {
> gimple_set_lhs (stmt, new_lhs);
> changed = true;
> }
> }
> }
>
> + fold_undefer_overflow_warnings (changed && !gimple_no_warning_p (stmt),
> + stmt, 0);
> return changed;
> }
>
> /* Valueziation callback that ends up not following SSA edges. */
>
> tree
> no_follow_ssa_edges (tree)
> {
> return NULL_TREE;
> }
> Index: trunk4/gcc/match.pd
> ===================================================================
> --- trunk4/gcc/match.pd (revision 235452)
> +++ trunk4/gcc/match.pd (working copy)
> @@ -3099,10 +3099,54 @@ DEFINE_INT_AND_FLOAT_ROUND_FN (RINT)
> (simplify
> /* signbit(x) -> 0 if x is nonnegative. */
> (SIGNBIT tree_expr_nonnegative_p@0)
> { integer_zero_node; })
>
> (simplify
> /* signbit(x) -> x<0 if x doesn't have signed zeros. */
> (SIGNBIT @0)
> (if (!HONOR_SIGNED_ZEROS (@0))
> (convert (lt @0 { build_real (TREE_TYPE (@0), dconst0); }))))
> +
> +/* Transform comparisons of the form X +- C1 CMP C2 to X CMP C2 -+ C1. */
> +(for cmp (eq ne)
> + (for op (plus minus)
> + rop (minus plus)
> + (simplify
> + (cmp (op@3 @0 INTEGER_CST@1) INTEGER_CST@2)
> + (if (!TREE_OVERFLOW (@1) && !TREE_OVERFLOW (@2)
> + && !TYPE_OVERFLOW_SANITIZED (TREE_TYPE (@0))
> + && !TYPE_OVERFLOW_TRAPS (TREE_TYPE (@0))
> + && !TYPE_SATURATING (TREE_TYPE (@0)))
> + (with { tree res = int_const_binop (rop, @2, @1); }
> + (if (TREE_OVERFLOW (res))
> + { constant_boolean_node (cmp == NE_EXPR, type); }
> + (if (single_use (@3))
> + (cmp @0 { res; }))))))))
> +(for cmp (lt le gt ge)
> + (for op (plus minus)
> + rop (minus plus)
> + (simplify
> + (cmp (op@3 @0 INTEGER_CST@1) INTEGER_CST@2)
> + (if (!TREE_OVERFLOW (@1) && !TREE_OVERFLOW (@2)
> + && TYPE_OVERFLOW_UNDEFINED (TREE_TYPE (@0)))
> + (with { tree res = int_const_binop (rop, @2, @1); }
> + (if (TREE_OVERFLOW (res))
> + {
> + fold_overflow_warning (("assuming signed overflow does not occur "
> + "when simplifying conditional to constant"),
> + WARN_STRICT_OVERFLOW_CONDITIONAL);
> + bool less = cmp == LE_EXPR || cmp == LT_EXPR;
> + /* wi::ges_p (@2, 0) should be sufficient for a signed type. */
> + bool ovf_high = wi::lt_p (@1, 0, TYPE_SIGN (TREE_TYPE (@1)))
> + != (op == MINUS_EXPR);
> + constant_boolean_node (less == ovf_high, type);
> + }
> + (if (single_use (@3))
> + (with
> + {
> + fold_overflow_warning (("assuming signed overflow does not occur "
> + "when changing X +- C1 cmp C2 to "
> + "X cmp C2 -+ C1"),
> + WARN_STRICT_OVERFLOW_COMPARISON);
> + }
> + (cmp @0 { res; })))))))))
> Index: trunk4/gcc/testsuite/gcc.dg/tree-ssa/20040305-1.c
> ===================================================================
> --- trunk4/gcc/testsuite/gcc.dg/tree-ssa/20040305-1.c (revision 235452)
> +++ trunk4/gcc/testsuite/gcc.dg/tree-ssa/20040305-1.c (working copy)
> @@ -16,15 +16,15 @@ void foo(int edx, int eax)
> }
> if (eax == 100)
> {
> if (-- edx == 0)
> afred[0] = 2;
> }
> }
>
>
> /* Verify that we did a forward propagation. */
> -/* { dg-final { scan-tree-dump-times "Replaced" 1 "forwprop1"} } */
> +/* { dg-final { scan-tree-dump-times "gimple_simplified" 1 "forwprop1"} }
> */
>
> /* After cddce we should have two IF statements remaining as the other
> two tests can be threaded. */
> /* { dg-final { scan-tree-dump-times "if " 2 "cddce2"} } */
>
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