https://gcc.gnu.org/bugzilla/show_bug.cgi?id=92712
--- Comment #17 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
Untested patch:
--- gcc/match.pd.jj 2019-11-05 14:59:22.546873967 +0100
+++ gcc/match.pd 2019-11-29 18:17:27.472002727 +0100
@@ -2480,18 +2480,42 @@ DEFINE_INT_AND_FLOAT_ROUND_FN (RINT)
(plusminus @0 (mult:c@3 @0 @2))
(if ((!ANY_INTEGRAL_TYPE_P (type)
|| TYPE_OVERFLOW_WRAPS (type)
+ /* For @0 + @0*@2 this transformation would introduce UB
+ (where there was none before) for @0 in [-1,0] and @2 max.
+ For @0 - @0*@2 this transformation would introduce UB
+ for @0 0 and @2 in [min,min+1] or @0 -1 and @2 min+1. */
|| (INTEGRAL_TYPE_P (type)
- && tree_expr_nonzero_p (@0)
- && expr_not_equal_to (@0, wi::minus_one (TYPE_PRECISION
(type)))))
+ && ((tree_expr_nonzero_p (@0)
+ && expr_not_equal_to (@0,
+ wi::minus_one (TYPE_PRECISION (type))))
+ || (plusminus == PLUS_EXPR
+ ? expr_not_equal_to (@2,
+ wi::max_value (TYPE_PRECISION (type), SIGNED))
+ /* Let's ignore the @0 -1 and @2 min case. */
+ : (expr_not_equal_to (@2,
+ wi::min_value (TYPE_PRECISION (type), SIGNED))
+ && expr_not_equal_to (@2,
+ wi::min_value (TYPE_PRECISION (type), SIGNED)
+ + 1))))))
&& single_use (@3))
(mult (plusminus { build_one_cst (type); } @2) @0)))
(simplify
(plusminus (mult:c@3 @0 @2) @0)
(if ((!ANY_INTEGRAL_TYPE_P (type)
|| TYPE_OVERFLOW_WRAPS (type)
+ /* For @0*@2 + @0 this transformation would introduce UB
+ (where there was none before) for @0 in [-1,0] and @2 max.
+ For @0*@2 - @0 this transformation would introduce UB
+ for @0 0 and @2 min. */
|| (INTEGRAL_TYPE_P (type)
- && tree_expr_nonzero_p (@0)
- && expr_not_equal_to (@0, wi::minus_one (TYPE_PRECISION
(type)))))
+ && ((tree_expr_nonzero_p (@0)
+ && (plusminus == MINUS_EXPR
+ || expr_not_equal_to (@0,
+ wi::minus_one (TYPE_PRECISION (type)))))
+ || expr_not_equal_to (@2,
+ (plusminus == PLUS_EXPR
+ ? wi::max_value (TYPE_PRECISION (type), SIGNED)
+ : wi::min_value (TYPE_PRECISION (type), SIGNED))))))
&& single_use (@3))
(mult (plusminus @2 { build_one_cst (type); }) @0))))))
This doesn't try to do anything about the A*B+A*C cases. Fixes the #c0
testcase and shows I've screwed up my simplified testcases,
the case that is fixed with this patch is e.g.
int foo (int t, int v)
{
int a = t - 1;
int b = a * v;
return b + v;
}
where we don't know anything about v (VARYING), but from a = t - 1 we know it
is not INT_MAX and can use that in the optimization.
