https://gcc.gnu.org/bugzilla/show_bug.cgi?id=81082
--- Comment #7 from Richard Biener <rguenth at gcc dot gnu.org> ---
FAIL: gcc.dg/tree-ssa/loop-15.c scan-tree-dump-times optimized " \\\\+ " 0
(found 2 times)
the loop is gone but we end up with unfolded
_1 = (unsigned int) n_5;
_10 = _1 + 4294967295;
_6 = (int) _10;
_13 = n_5 * _6;
j_2 = n_5 + _13;
which is when you decipher, just (n * (n - 1)) + n == n * n
FAIL: gcc.dg/tree-ssa/pr23294.c scan-tree-dump-not optimized "\\\\* 6"
FAIL: gcc.dg/tree-ssa/pr23294.c scan-tree-dump-times optimized " \\\\* 2" 3
(found 4 times)
FAIL: gcc.dg/tree-ssa/pr23294.c scan-tree-dump-times optimized "a_..D. \\\\* 5"
3 (found 0 times)
my patterns are incomplete and don't for example handle
_1 = a_2(D) * 6;
_3 = _1 - a_2(D);
where it isn't important whether a_2 is zero or -1. Leaving these cases
to fold-const.c might be best at this point(?).
FAIL: gcc.dg/tree-ssa/pr63586-2.c scan-tree-dump-times reassoc1 "\\\\* 6" 1
(found 0 times)
Similar.
FAIL: gcc.dg/tree-ssa/slsr-3.c scan-tree-dump-times optimized "\\\\* 4" 1
(found 4 times)
FAIL: gcc.dg/tree-ssa/slsr-3.c scan-tree-dump-times optimized "\\\\+ 12|\\\\,
12>" 1 (found 0 times)
FAIL: gcc.dg/tree-ssa/slsr-3.c scan-tree-dump-times optimized "\\\\+ 4|\\\\,
4>" 2 (found 1 times)
FAIL: gcc.dg/tree-ssa/slsr-3.c scan-tree-dump-times optimized "\\\\+ 8|\\\\,
8>" 1 (found 0 times)
FAIL: gcc.dg/tree-ssa/slsr-4.c scan-tree-dump-times optimized "\\\\* 40" 1
(found 2 times)
FAIL: gcc.dg/tree-ssa/slsr-4.c scan-tree-dump-times optimized "\\\\+ 40" 1
(found 0 times)
FAIL: gfortran.dg/reassoc_4.f -O scan-tree-dump-times reassoc1 "[0-9] \\\\*
" 22 (found 23 times)
Leaves us with those FAILs. Thus adjusted fold-const.c hunk would be
Index: gcc/fold-const.c
===================================================================
--- gcc/fold-const.c (revision 256977)
+++ gcc/fold-const.c (working copy)
@@ -7097,7 +7097,7 @@ fold_plusminus_mult_expr (location_t loc
/* Same may be zero and thus the operation 'code' may overflow. Likewise
same may be minus one and thus the multiplication may overflow. Perform
- the operations in an unsigned type. */
+ the sum operation in an unsigned type. */
tree utype = unsigned_type_for (type);
tree tem = fold_build2_loc (loc, code, utype,
fold_convert_loc (loc, utype, alt0),
@@ -7110,9 +7110,9 @@ fold_plusminus_mult_expr (location_t loc
return fold_build2_loc (loc, MULT_EXPR, type,
fold_convert (type, tem), same);
- return fold_convert_loc (loc, type,
- fold_build2_loc (loc, MULT_EXPR, utype, tem,
- fold_convert_loc (loc, utype,
same)));
+ /* Do not resort to unsigned multiplication because
+ we lose the no-overflow property of the expression. */
+ return NULL_TREE;
}
/* Subroutine of native_encode_expr. Encode the INTEGER_CST
