From: Kyrylo Tkachov <[email protected]>
X - MIN (X, Y) is unsigned saturating subtraction, but subtraction
statements were not checked for this form.
Recognize the form and check MINUS_EXPR statements for saturation. Require
the MIN to have one use so that the replacement removes it. If a replacement
changes the current statement, do not try to widen that statement.
AArch64 -O2:
before:
cmp w1, w0
csel w1, w1, w0, ls
sub w0, w0, w1
after:
subs w0, w0, w1
csel w0, w0, wzr, cs
The vector form becomes one UQSUB instead of a comparison, a select, and a
subtraction.
Bootstrapped and tested on aarch64-none-linux-gnu.
Ok for trunk?
gcc/ChangeLog:
* match-sat-alu.pd (unsigned_integer_sat_sub): Add the
X - MIN (X, Y) form.
* tree-ssa-math-opts.cc
(math_opts_dom_walker::before_dom_children): Call
match_unsigned_saturation_sub for MINUS_EXPR as well, and
only widen while the statement is unchanged.
gcc/testsuite/ChangeLog:
* gcc.target/aarch64/sat_u_sub_minmax-1.c: New test.
* gcc.target/aarch64/sat_u_sub_minmax-2.c: New test.
* gcc.target/aarch64/sat_u_sub_minmax-3.c: New test.
Signed-off-by: Kyrylo Tkachov <[email protected]>
---
gcc/match-sat-alu.pd | 6 ++++
.../gcc.target/aarch64/sat_u_sub_minmax-1.c | 18 +++++++++++
.../gcc.target/aarch64/sat_u_sub_minmax-2.c | 32 +++++++++++++++++++
.../gcc.target/aarch64/sat_u_sub_minmax-3.c | 27 ++++++++++++++++
gcc/tree-ssa-math-opts.cc | 5 +--
5 files changed, 86 insertions(+), 2 deletions(-)
create mode 100644 gcc/testsuite/gcc.target/aarch64/sat_u_sub_minmax-1.c
create mode 100644 gcc/testsuite/gcc.target/aarch64/sat_u_sub_minmax-2.c
create mode 100644 gcc/testsuite/gcc.target/aarch64/sat_u_sub_minmax-3.c
diff --git a/gcc/match-sat-alu.pd b/gcc/match-sat-alu.pd
index 7156529f589..1b35b35cff8 100644
--- a/gcc/match-sat-alu.pd
+++ b/gcc/match-sat-alu.pd
@@ -131,6 +131,12 @@ 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))))
+ (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
+ replacing it, which costs an instruction. */
+ (minus @0 (min:c@2 @0 @1))
+ (if (single_use (@2))))
(match (unsigned_integer_sat_sub @0 @1)
/* DIFF = SUB_OVERFLOW (X, Y)
SAT_U_SUB = REALPART (DIFF) | (IMAGPART (DIFF) + (-1)) */
diff --git a/gcc/testsuite/gcc.target/aarch64/sat_u_sub_minmax-1.c
b/gcc/testsuite/gcc.target/aarch64/sat_u_sub_minmax-1.c
new file mode 100644
index 00000000000..aa1d7b6f031
--- /dev/null
+++ b/gcc/testsuite/gcc.target/aarch64/sat_u_sub_minmax-1.c
@@ -0,0 +1,18 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -fdump-tree-optimized" } */
+
+#define DEF_MIN(T) \
+ T min_##T (T a, T b) { return a - (a < b ? a : b); } \
+ T nim_##T (T a, T b) { return a - (b < a ? b : a); }
+
+typedef unsigned char u8;
+typedef unsigned short u16;
+typedef unsigned int u32;
+typedef unsigned long long u64;
+
+DEF_MIN (u8)
+DEF_MIN (u16)
+DEF_MIN (u32)
+DEF_MIN (u64)
+
+/* { dg-final { scan-tree-dump-times "\\.SAT_SUB " 8 "optimized" } } */
diff --git a/gcc/testsuite/gcc.target/aarch64/sat_u_sub_minmax-2.c
b/gcc/testsuite/gcc.target/aarch64/sat_u_sub_minmax-2.c
new file mode 100644
index 00000000000..dcf8ab46309
--- /dev/null
+++ b/gcc/testsuite/gcc.target/aarch64/sat_u_sub_minmax-2.c
@@ -0,0 +1,32 @@
+/* { dg-do compile } */
+/* { dg-options "-O3 -fdump-tree-optimized" } */
+
+typedef unsigned char u8;
+typedef unsigned int u32;
+
+/* The recognition must reach the vectoriser, so that the loop becomes a
+ single uqsub rather than a compare, a select and a subtraction. */
+
+void
+min_loop (u8 *__restrict d, u8 *__restrict a, u8 *__restrict b, int n)
+{
+ for (int i = 0; i < n; i++)
+ {
+ u8 x = a[i], y = b[i];
+ d[i] = x - (x < y ? x : y);
+ }
+}
+
+void
+min_loop32 (u32 *__restrict d, u32 *__restrict a, u32 *__restrict b, int n)
+{
+ for (int i = 0; i < n; i++)
+ {
+ u32 x = a[i], y = b[i];
+ d[i] = x - (y < x ? y : x);
+ }
+}
+
+/* { dg-final { scan-tree-dump "\\.SAT_SUB " "optimized" } } */
+/* { dg-final { scan-assembler "uqsub\tv\[0-9\]+\\.16b" } } */
+/* { dg-final { scan-assembler "uqsub\tv\[0-9\]+\\.4s" } } */
diff --git a/gcc/testsuite/gcc.target/aarch64/sat_u_sub_minmax-3.c
b/gcc/testsuite/gcc.target/aarch64/sat_u_sub_minmax-3.c
new file mode 100644
index 00000000000..029c136b7d0
--- /dev/null
+++ b/gcc/testsuite/gcc.target/aarch64/sat_u_sub_minmax-3.c
@@ -0,0 +1,27 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -fdump-tree-optimized" } */
+
+typedef unsigned int u32;
+
+/* While the MIN stays live the saturating subtract would be computed beside
+ it rather than instead of it, so the rules do not fire. */
+
+u32
+min_live (u32 a, u32 b, u32 *o)
+{
+ u32 m = a < b ? a : b;
+ *o = m;
+ return a - m;
+}
+
+u32
+add_min_live (u32 a, u32 b, u32 *o)
+{
+ u32 t = ~a;
+ u32 m = b < t ? b : t;
+ *o = m;
+ return a + m;
+}
+
+/* { dg-final { scan-tree-dump-not "\\.SAT_SUB " "optimized" } } */
+/* { dg-final { scan-tree-dump-not "\\.SAT_ADD " "optimized" } } */
diff --git a/gcc/tree-ssa-math-opts.cc b/gcc/tree-ssa-math-opts.cc
index b371b5b7cff..ed3abb7d5c4 100644
--- a/gcc/tree-ssa-math-opts.cc
+++ b/gcc/tree-ssa-math-opts.cc
@@ -7332,10 +7332,11 @@ math_opts_dom_walker::after_dom_children (basic_block
bb)
case PLUS_EXPR:
match_saturation_add_with_assign (&gsi, as_a<gassign *> (stmt));
- match_unsigned_saturation_sub (&gsi, as_a<gassign *> (stmt));
/* fall-through */
case MINUS_EXPR:
- if (!convert_plusminus_to_widen (&gsi, stmt, code))
+ match_unsigned_saturation_sub (&gsi, as_a<gassign *> (stmt));
+ if (gsi_stmt (gsi) == stmt
+ && !convert_plusminus_to_widen (&gsi, stmt, code))
{
match_arith_overflow (&gsi, stmt, code, m_cfg_changed_p);
if (gsi_stmt (gsi) == stmt)
--
2.50.1 (Apple Git-155)
