This patch adds a new case for unsigned scalar saturating subtraction
using a branch with a greater-than-or-equal condition. For example,
X >= (X - Y) ? (X - Y) : 0
is transformed into SAT_SUB (X, Y) when X and Y are unsigned scalars,
which therefore correctly matches more cases of IFN SAT_SUB.
This passes the aarch64-none-linux-gnu regression tests with no failures.
gcc/ChangeLog:
* match.pd: Add new match for SAT_SUB.
---
gcc/match.pd | 8 ++++++++
1 file changed, 8 insertions(+)
diff --git a/gcc/match.pd b/gcc/match.pd
index ee53c25cef9..4fc5efa6247 100644
--- a/gcc/match.pd
+++ b/gcc/match.pd
@@ -3360,6 +3360,14 @@ DEFINE_INT_AND_FLOAT_ROUND_FN (RINT)
}
(if (wi::eq_p (sum, wi::uhwi (0, precision)))))))
+/* Unsigned saturation sub, case 11 (branch with ge):
+ SAT_U_SUB = X >= (X - Y) ? (X - Y) : 0. */
+(match (unsigned_integer_sat_sub @0 @1)
+ (cond^ (ge @0 (minus @0 @1))
+ (convert? (minus (convert1? @0) (convert1? @1))) integer_zerop)
+ (if (INTEGRAL_TYPE_P (type) && TYPE_UNSIGNED (type)
+ && TYPE_UNSIGNED (TREE_TYPE (@0)) && types_match (@0, @1))))
+
/* Signed saturation sub, case 1:
T minus = (T)((UT)X - (UT)Y);
SAT_S_SUB = (X ^ Y) & (X ^ minus) < 0 ? (-(T)(X < 0) ^ MAX) : minus;
--
2.34.1
