diff mbox series

[04/13] match-sat-alu.pd: Recognize borrow-test saturating subtraction

Message ID 20260902145254.77832-6-ktkachov@nvidia.com
State New
Headers show
Series Saturating arithmetic matching improvements | expand

Commit Message

Kyrylo Tkachov Sept. 2, 2026, 2:52 p.m. UTC 
From: Kyrylo Tkachov <ktkachov@nvidia.com>

For unsigned subtraction, the wrapped difference is greater than the minuend
exactly when the subtraction borrows.  These forms are therefore saturating
subtraction:

  R = X - Y
  R > X ? 0 : R
  R <= X ? R : 0

Recognize both comparison operand orders and both result arm orders.

AArch64 -O3, vector body:

before:

	sub	v30.4s, v31.4s, v30.4s
	cmhs	v31.4s, v31.4s, v30.4s
	and	v31.16b, v31.16b, v30.16b

after:

	uqsub	v30.4s, v31.4s, v30.4s

Three vector operations become one.
Remove four existing expected-failure markers for the supported forms.

Bootstrapped and tested on aarch64-none-linux-gnu.

Ok for trunk?

gcc/ChangeLog:

	* match-sat-alu.pd (unsigned_integer_sat_sub): Add the four
	forms that compare the difference with the minuend.

gcc/testsuite/ChangeLog:

	* gcc.target/aarch64/sat_u_sub_borrow-1.c: New test.
	* gcc.target/aarch64/saturating_arithmetic_1.c: Remove the xfail
	on usub.
	* gcc.target/aarch64/sve/saturating_arithmetic_1.c: Remove the
	xfail on usubq.
	* gcc.target/aarch64/sve/saturating_arithmetic_3.c: Likewise.
	* gcc.target/aarch64/sve/saturating_arithmetic_4.c: Likewise.

Signed-off-by: Kyrylo Tkachov <ktkachov@nvidia.com>
---
 gcc/match-sat-alu.pd                          |  9 ++++++++
 .../gcc.target/aarch64/sat_u_sub_borrow-1.c   | 22 +++++++++++++++++++
 .../aarch64/saturating_arithmetic_1.c         |  2 +-
 .../aarch64/sve/saturating_arithmetic_1.c     |  2 +-
 .../aarch64/sve/saturating_arithmetic_3.c     |  2 +-
 .../aarch64/sve/saturating_arithmetic_4.c     |  2 +-
 6 files changed, 35 insertions(+), 4 deletions(-)
 create mode 100644 gcc/testsuite/gcc.target/aarch64/sat_u_sub_borrow-1.c

Comments

Andrea Pinski Sept. 3, 2026, 6:21 a.m. UTC | #1 
On Wed, Sep 2, 2026 at 7:55 AM <ktkachov@nvidia.com> wrote:
>
> From: Kyrylo Tkachov <ktkachov@nvidia.com>
>
> For unsigned subtraction, the wrapped difference is greater than the minuend
> exactly when the subtraction borrows.  These forms are therefore saturating
> subtraction:
>
>   R = X - Y
>   R > X ? 0 : R
>   R <= X ? R : 0
>
> Recognize both comparison operand orders and both result arm orders.
>
> AArch64 -O3, vector body:
>
> before:
>
>         sub     v30.4s, v31.4s, v30.4s
>         cmhs    v31.4s, v31.4s, v30.4s
>         and     v31.16b, v31.16b, v30.16b
>
> after:
>
>         uqsub   v30.4s, v31.4s, v30.4s
>
> Three vector operations become one.
> Remove four existing expected-failure markers for the supported forms.
>
> Bootstrapped and tested on aarch64-none-linux-gnu.
>
> Ok for trunk?

Ok.

>
> gcc/ChangeLog:
>
>         * match-sat-alu.pd (unsigned_integer_sat_sub): Add the four
>         forms that compare the difference with the minuend.
>
> gcc/testsuite/ChangeLog:
>
>         * gcc.target/aarch64/sat_u_sub_borrow-1.c: New test.
>         * gcc.target/aarch64/saturating_arithmetic_1.c: Remove the xfail
>         on usub.
>         * gcc.target/aarch64/sve/saturating_arithmetic_1.c: Remove the
>         xfail on usubq.
>         * gcc.target/aarch64/sve/saturating_arithmetic_3.c: Likewise.
>         * gcc.target/aarch64/sve/saturating_arithmetic_4.c: Likewise.
>
> Signed-off-by: Kyrylo Tkachov <ktkachov@nvidia.com>
> ---
>  gcc/match-sat-alu.pd                          |  9 ++++++++
>  .../gcc.target/aarch64/sat_u_sub_borrow-1.c   | 22 +++++++++++++++++++
>  .../aarch64/saturating_arithmetic_1.c         |  2 +-
>  .../aarch64/sve/saturating_arithmetic_1.c     |  2 +-
>  .../aarch64/sve/saturating_arithmetic_3.c     |  2 +-
>  .../aarch64/sve/saturating_arithmetic_4.c     |  2 +-
>  6 files changed, 35 insertions(+), 4 deletions(-)
>  create mode 100644 gcc/testsuite/gcc.target/aarch64/sat_u_sub_borrow-1.c
>
> diff --git a/gcc/match-sat-alu.pd b/gcc/match-sat-alu.pd
> index 8c7bc0782a0..dfb2eb9800f 100644
> --- a/gcc/match-sat-alu.pd
> +++ b/gcc/match-sat-alu.pd
> @@ -131,6 +131,15 @@ along with GCC; see the file COPYING3.  If not see
>    /* SAT_U_SUB = (X - Y) * (X >= Y)  */
>    (mult:c (minus @0 @1) (convert (ge @0 @1)))
>    (if (types_match (type, @0, @1))))
> + /* The wrapped difference exceeds the minuend exactly when the subtraction
> +    borrows, so a source that names the difference and then tests it against
> +    the minuend is a saturating subtract.  */
> + (match (unsigned_integer_sat_sub @0 @1)
> +  /* SAT_U_SUB = (X - Y) > X ? 0 : X - Y, and the commuted comparison.  */
> +  (cond^ (gt:c (minus@2 @0 @1) @0) integer_zerop @2))
> + (match (unsigned_integer_sat_sub @0 @1)
> +  /* SAT_U_SUB = (X - Y) <= X ? X - Y : 0, and the commuted comparison.  */
> +  (cond^ (le:c (minus@2 @0 @1) @0) @2 integer_zerop))
>   (match (unsigned_integer_sat_sub @0 @1)
>    /* SAT_U_SUB = X - MIN (X, Y).  The MIN has to be single use: while it
>       stays live the saturating subtract is computed beside it instead of
> diff --git a/gcc/testsuite/gcc.target/aarch64/sat_u_sub_borrow-1.c b/gcc/testsuite/gcc.target/aarch64/sat_u_sub_borrow-1.c
> new file mode 100644
> index 00000000000..8b86cb92922
> --- /dev/null
> +++ b/gcc/testsuite/gcc.target/aarch64/sat_u_sub_borrow-1.c
> @@ -0,0 +1,22 @@
> +/* { dg-do compile } */
> +/* { dg-options "-O2 -fdump-tree-optimized" } */
> +
> +typedef unsigned char u8;
> +typedef unsigned short u16;
> +typedef unsigned int u32;
> +typedef unsigned long long u64;
> +
> +/* The wrapped difference is larger than the minuend exactly when the
> +   subtraction borrowed, so each of these is a saturating subtract.  */
> +
> +#define DEF(N, T)                                              \
> +  T f1_##N (T a, T b) { T r = a - b; return r > a ? 0 : r; }   \
> +  T f2_##N (T a, T b) { T r = a - b; if (r > a) r = 0; return r; } \
> +  T f3_##N (T a, T b) { T r = a - b; return r <= a ? r : 0; }
> +
> +DEF (8, u8)
> +DEF (16, u16)
> +DEF (32, u32)
> +DEF (64, u64)
> +
> +/* { dg-final { scan-tree-dump-times "\\.SAT_SUB " 12 "optimized" } } */
> diff --git a/gcc/testsuite/gcc.target/aarch64/saturating_arithmetic_1.c b/gcc/testsuite/gcc.target/aarch64/saturating_arithmetic_1.c
> index 8fc1569845b..c73a024edec 100644
> --- a/gcc/testsuite/gcc.target/aarch64/saturating_arithmetic_1.c
> +++ b/gcc/testsuite/gcc.target/aarch64/saturating_arithmetic_1.c
> @@ -19,7 +19,7 @@
>  **     ret
>  */
>  /*
> -** usub: { xfail *-*-* }
> +** usub:
>  **     dup     v([0-9]+).8b, w[01]
>  **     dup     v([0-9]+).8b, w[01]
>  **     uqsub   b([0-9]+), b\1, b\2
> diff --git a/gcc/testsuite/gcc.target/aarch64/sve/saturating_arithmetic_1.c b/gcc/testsuite/gcc.target/aarch64/sve/saturating_arithmetic_1.c
> index 6936e9a2704..4cfab740c40 100644
> --- a/gcc/testsuite/gcc.target/aarch64/sve/saturating_arithmetic_1.c
> +++ b/gcc/testsuite/gcc.target/aarch64/sve/saturating_arithmetic_1.c
> @@ -39,7 +39,7 @@
>  ** ...
>  */
>  /*
> -** usubq: { xfail *-*-* }
> +** usubq:
>  ** ...
>  **     ld1b\tz([0-9]+)\.b, .*
>  **     ld1b\tz([0-9]+)\.b, .*
> diff --git a/gcc/testsuite/gcc.target/aarch64/sve/saturating_arithmetic_3.c b/gcc/testsuite/gcc.target/aarch64/sve/saturating_arithmetic_3.c
> index 14e2de59b1e..def7c82e256 100644
> --- a/gcc/testsuite/gcc.target/aarch64/sve/saturating_arithmetic_3.c
> +++ b/gcc/testsuite/gcc.target/aarch64/sve/saturating_arithmetic_3.c
> @@ -40,7 +40,7 @@
>  ** ...
>  */
>  /*
> -** usubq: { xfail *-*-* }
> +** usubq:
>  ** ...
>  **     ld1w\tz([0-9]+)\.s, .*
>  **     ld1w\tz([0-9]+)\.s, .*
> diff --git a/gcc/testsuite/gcc.target/aarch64/sve/saturating_arithmetic_4.c b/gcc/testsuite/gcc.target/aarch64/sve/saturating_arithmetic_4.c
> index 05a5786b4ab..5b9f8740ed4 100644
> --- a/gcc/testsuite/gcc.target/aarch64/sve/saturating_arithmetic_4.c
> +++ b/gcc/testsuite/gcc.target/aarch64/sve/saturating_arithmetic_4.c
> @@ -40,7 +40,7 @@
>  ** ...
>  */
>  /*
> -** usubq: { xfail *-*-* }
> +** usubq:
>  ** ...
>  **     ld1d\tz([0-9]+)\.d, .*
>  **     ld1d\tz([0-9]+)\.d, .*
> --
> 2.50.1 (Apple Git-155)
>
diff mbox series

Patch

diff --git a/gcc/match-sat-alu.pd b/gcc/match-sat-alu.pd
index 8c7bc0782a0..dfb2eb9800f 100644
--- a/gcc/match-sat-alu.pd
+++ b/gcc/match-sat-alu.pd
@@ -131,6 +131,15 @@  along with GCC; see the file COPYING3.  If not see
   /* SAT_U_SUB = (X - Y) * (X >= Y)  */
   (mult:c (minus @0 @1) (convert (ge @0 @1)))
   (if (types_match (type, @0, @1))))
+ /* The wrapped difference exceeds the minuend exactly when the subtraction
+    borrows, so a source that names the difference and then tests it against
+    the minuend is a saturating subtract.  */
+ (match (unsigned_integer_sat_sub @0 @1)
+  /* SAT_U_SUB = (X - Y) > X ? 0 : X - Y, and the commuted comparison.  */
+  (cond^ (gt:c (minus@2 @0 @1) @0) integer_zerop @2))
+ (match (unsigned_integer_sat_sub @0 @1)
+  /* SAT_U_SUB = (X - Y) <= X ? X - Y : 0, and the commuted comparison.  */
+  (cond^ (le:c (minus@2 @0 @1) @0) @2 integer_zerop))
  (match (unsigned_integer_sat_sub @0 @1)
   /* SAT_U_SUB = X - MIN (X, Y).  The MIN has to be single use: while it
      stays live the saturating subtract is computed beside it instead of
diff --git a/gcc/testsuite/gcc.target/aarch64/sat_u_sub_borrow-1.c b/gcc/testsuite/gcc.target/aarch64/sat_u_sub_borrow-1.c
new file mode 100644
index 00000000000..8b86cb92922
--- /dev/null
+++ b/gcc/testsuite/gcc.target/aarch64/sat_u_sub_borrow-1.c
@@ -0,0 +1,22 @@ 
+/* { dg-do compile } */
+/* { dg-options "-O2 -fdump-tree-optimized" } */
+
+typedef unsigned char u8;
+typedef unsigned short u16;
+typedef unsigned int u32;
+typedef unsigned long long u64;
+
+/* The wrapped difference is larger than the minuend exactly when the
+   subtraction borrowed, so each of these is a saturating subtract.  */
+
+#define DEF(N, T)						\
+  T f1_##N (T a, T b) { T r = a - b; return r > a ? 0 : r; }	\
+  T f2_##N (T a, T b) { T r = a - b; if (r > a) r = 0; return r; } \
+  T f3_##N (T a, T b) { T r = a - b; return r <= a ? r : 0; }
+
+DEF (8, u8)
+DEF (16, u16)
+DEF (32, u32)
+DEF (64, u64)
+
+/* { dg-final { scan-tree-dump-times "\\.SAT_SUB " 12 "optimized" } } */
diff --git a/gcc/testsuite/gcc.target/aarch64/saturating_arithmetic_1.c b/gcc/testsuite/gcc.target/aarch64/saturating_arithmetic_1.c
index 8fc1569845b..c73a024edec 100644
--- a/gcc/testsuite/gcc.target/aarch64/saturating_arithmetic_1.c
+++ b/gcc/testsuite/gcc.target/aarch64/saturating_arithmetic_1.c
@@ -19,7 +19,7 @@ 
 **	ret
 */
 /*
-** usub: { xfail *-*-* }
+** usub:
 **	dup	v([0-9]+).8b, w[01]
 **	dup	v([0-9]+).8b, w[01]
 **	uqsub	b([0-9]+), b\1, b\2
diff --git a/gcc/testsuite/gcc.target/aarch64/sve/saturating_arithmetic_1.c b/gcc/testsuite/gcc.target/aarch64/sve/saturating_arithmetic_1.c
index 6936e9a2704..4cfab740c40 100644
--- a/gcc/testsuite/gcc.target/aarch64/sve/saturating_arithmetic_1.c
+++ b/gcc/testsuite/gcc.target/aarch64/sve/saturating_arithmetic_1.c
@@ -39,7 +39,7 @@ 
 ** ...
 */
 /*
-** usubq: { xfail *-*-* }
+** usubq:
 ** ...
 **	ld1b\tz([0-9]+)\.b, .*
 **	ld1b\tz([0-9]+)\.b, .*
diff --git a/gcc/testsuite/gcc.target/aarch64/sve/saturating_arithmetic_3.c b/gcc/testsuite/gcc.target/aarch64/sve/saturating_arithmetic_3.c
index 14e2de59b1e..def7c82e256 100644
--- a/gcc/testsuite/gcc.target/aarch64/sve/saturating_arithmetic_3.c
+++ b/gcc/testsuite/gcc.target/aarch64/sve/saturating_arithmetic_3.c
@@ -40,7 +40,7 @@ 
 ** ...
 */
 /*
-** usubq: { xfail *-*-* }
+** usubq:
 ** ...
 **	ld1w\tz([0-9]+)\.s, .*
 **	ld1w\tz([0-9]+)\.s, .*
diff --git a/gcc/testsuite/gcc.target/aarch64/sve/saturating_arithmetic_4.c b/gcc/testsuite/gcc.target/aarch64/sve/saturating_arithmetic_4.c
index 05a5786b4ab..5b9f8740ed4 100644
--- a/gcc/testsuite/gcc.target/aarch64/sve/saturating_arithmetic_4.c
+++ b/gcc/testsuite/gcc.target/aarch64/sve/saturating_arithmetic_4.c
@@ -40,7 +40,7 @@ 
 ** ...
 */
 /*
-** usubq: { xfail *-*-* }
+** usubq:
 ** ...
 **	ld1d\tz([0-9]+)\.d, .*
 **	ld1d\tz([0-9]+)\.d, .*