We vectorise:
int
f (int *a, int n)
{
int count = 0;
for (int i = 0; i < n; ++i)
if (a[i] < 255)
count += 1;
return count;
}
using an add reduction of a VEC_COND_EXPR <COND, {1, 1, ...}, {0, 0, ...}>.
This leads to the main loop having an AND with a loop invariant {1, 1, ...}.
E.g. on aarch64:
movi v2.4s, 0x1
.L4:
lsl x5, x4, 4
add x4, x4, 1
cmp w2, w4
ldr q1, [x0, x5]
cmge v1.4s, v3.4s, v1.4s
and v1.16b, v2.16b, v1.16b
add v0.4s, v0.4s, v1.4s
bhi .L4
This patch converts an ADD of that VEC_COND_EXPR into a SUB of COND:
.L4:
lsl x5, x4, 4
add x4, x4, 1
cmp w2, w4
ldr q1, [x0, x5]
cmge v1.4s, v2.4s, v1.4s
sub v0.4s, v0.4s, v1.4s
bhi .L4
At the moment the simplification is done during forwprop4, after the last
dce pass, and so the VEC_COND_EXPR survives until expand. Richi says
this a known problem. Of course, the expression gets deleted by
rtl dce, but it means that a scan-tree-dump of the *.optimized output
can't easily tell that the optimisation has triggered. I've therefore
added a scan-assembler test instead.
Bootstrapped & regression-tested on x86_64-linux-gnu. Also tested
on aarch64-elf. OK to install?
Thanks,
Richard
gcc/
* match.pd: Add patterns for vec_conds between -1 and 0, and
between 1 and 0.
gcc/testsuite/
* gcc.target/aarch64/vect-add-sub-cond.c: New test.
Index: gcc/match.pd
===================================================================
--- gcc/match.pd 2015-06-23 11:42:23.644645975 +0100
+++ gcc/match.pd 2015-06-23 11:42:23.760644655 +0100
@@ -973,6 +973,36 @@ along with GCC; see the file COPYING3.
(cnd @0 @2 @1)))
+/* Vector comparisons are defined to produce all-one or all-zero results. */
+(simplify
+ (vec_cond @0 integer_all_onesp@1 integer_zerop@2)
+ (if (tree_nop_conversion_p (type, TREE_TYPE (@0)))
+ (convert @0)))
+
+/* We could instead convert all instances of the vec_cond to negate,
+ but that isn't necessarily a win on its own. */
+(simplify
+ (plus:c @3 (vec_cond @0 integer_each_onep@1 integer_zerop@2))
+ (if (tree_nop_conversion_p (type, TREE_TYPE (@0)))
+ (minus @3 (convert @0))))
+
+(simplify
+ (plus:c @3 (view_convert_expr
+ (vec_cond @0 integer_each_onep@1 integer_zerop@2)))
+ (if (tree_nop_conversion_p (type, TREE_TYPE (@0)))
+ (minus @3 (convert @0))))
+
+(simplify
+ (minus @3 (vec_cond @0 integer_each_onep@1 integer_zerop@2))
+ (if (tree_nop_conversion_p (type, TREE_TYPE (@0)))
+ (plus @3 (convert @0))))
+
+(simplify
+ (minus @3 (view_convert_expr
+ (vec_cond @0 integer_each_onep@1 integer_zerop@2)))
+ (if (tree_nop_conversion_p (type, TREE_TYPE (@0)))
+ (plus @3 (convert @0))))
+
/* Simplifications of comparisons. */
/* We can simplify a logical negation of a comparison to the
Index: gcc/testsuite/gcc.target/aarch64/vect-add-sub-cond.c
===================================================================
--- /dev/null 2015-06-02 17:27:28.541944012 +0100
+++ gcc/testsuite/gcc.target/aarch64/vect-add-sub-cond.c 2015-06-23
12:06:27.120203685 +0100
@@ -0,0 +1,94 @@
+/* Make sure that vector comaprison results are not unnecessarily ANDed
+ with vectors of 1. */
+/* { dg-do compile } */
+/* { dg-options "-O2 -ftree-vectorize" } */
+
+#define COUNT1(X) if (X) count += 1
+#define COUNT2(X) if (X) count -= 1
+#define COUNT3(X) count += (X)
+#define COUNT4(X) count -= (X)
+
+#define COND1(X) (X)
+#define COND2(X) ((X) ? 1 : 0)
+#define COND3(X) ((X) ? -1 : 0)
+#define COND4(X) ((X) ? 0 : 1)
+#define COND5(X) ((X) ? 0 : -1)
+
+#define TEST_LT(X, Y) ((X) < (Y))
+#define TEST_LE(X, Y) ((X) <= (Y))
+#define TEST_GT(X, Y) ((X) > (Y))
+#define TEST_GE(X, Y) ((X) >= (Y))
+#define TEST_EQ(X, Y) ((X) == (Y))
+#define TEST_NE(X, Y) ((X) != (Y))
+
+#define COUNT_LOOP(ID, TYPE, CMP_ARRAY, TEST, COUNT) \
+ TYPE \
+ reduc_##ID (__typeof__ (CMP_ARRAY[0]) x) \
+ { \
+ TYPE count = 0; \
+ for (unsigned int i = 0; i < 1024; ++i) \
+ COUNT (TEST (CMP_ARRAY[i], x)); \
+ return count; \
+ }
+
+#define COND_LOOP(ID, ARRAY, CMP_ARRAY, TEST, COND) \
+ void \
+ plus_##ID (__typeof__ (CMP_ARRAY[0]) x) \
+ { \
+ for (unsigned int i = 0; i < 1024; ++i) \
+ ARRAY[i] += COND (TEST (CMP_ARRAY[i], x)); \
+ } \
+ void \
+ plusc_##ID (void) \
+ { \
+ for (unsigned int i = 0; i < 1024; ++i) \
+ ARRAY[i] += COND (TEST (CMP_ARRAY[i], 10)); \
+ } \
+ void \
+ minus_##ID (__typeof__ (CMP_ARRAY[0]) x) \
+ { \
+ for (unsigned int i = 0; i < 1024; ++i) \
+ ARRAY[i] -= COND (TEST (CMP_ARRAY[i], x)); \
+ } \
+ void \
+ minusc_##ID (void) \
+ { \
+ for (unsigned int i = 0; i < 1024; ++i) \
+ ARRAY[i] += COND (TEST (CMP_ARRAY[i], 1)); \
+ }
+
+#define ALL_LOOPS(ID, ARRAY, CMP_ARRAY, TEST) \
+ typedef __typeof__(ARRAY[0]) ID##_type; \
+ COUNT_LOOP (ID##_1, ID##_type, CMP_ARRAY, TEST, COUNT1) \
+ COUNT_LOOP (ID##_2, ID##_type, CMP_ARRAY, TEST, COUNT2) \
+ COUNT_LOOP (ID##_3, ID##_type, CMP_ARRAY, TEST, COUNT3) \
+ COUNT_LOOP (ID##_4, ID##_type, CMP_ARRAY, TEST, COUNT4) \
+ COND_LOOP (ID##_1, ARRAY, CMP_ARRAY, TEST, COND1) \
+ COND_LOOP (ID##_2, ARRAY, CMP_ARRAY, TEST, COND2) \
+ COND_LOOP (ID##_3, ARRAY, CMP_ARRAY, TEST, COND3) \
+ COND_LOOP (ID##_4, ARRAY, CMP_ARRAY, TEST, COND4) \
+ COND_LOOP (ID##_5, ARRAY, CMP_ARRAY, TEST, COND5)
+
+signed int asi[1024] __attribute__ ((aligned (16)));
+unsigned int aui[1024] __attribute__ ((aligned (16)));
+signed long long asl[1024] __attribute__ ((aligned (16)));
+unsigned long long aul[1024] __attribute__ ((aligned (16)));
+float af[1024] __attribute__ ((aligned (16)));
+double ad[1024] __attribute__ ((aligned (16)));
+
+ALL_LOOPS (si_si, aui, asi, TEST_LT)
+ALL_LOOPS (ui_si, aui, asi, TEST_LE)
+ALL_LOOPS (si_ui, aui, asi, TEST_GT)
+ALL_LOOPS (ui_ui, aui, asi, TEST_GE)
+ALL_LOOPS (sl_sl, asl, asl, TEST_NE)
+ALL_LOOPS (ul_ul, aul, aul, TEST_NE)
+ALL_LOOPS (si_f, asi, af, TEST_LE)
+ALL_LOOPS (ui_f, aui, af, TEST_GT)
+ALL_LOOPS (sl_d, asl, ad, TEST_GE)
+ALL_LOOPS (ul_d, aul, ad, TEST_GT)
+
+/* { dg-final { scan-assembler-not "\tand\t" } } */
+/* { dg-final { scan-assembler-not "\tld\[^\t\]*\t\[wx\]" } } */
+/* { dg-final { scan-assembler-not "\tst\[^\t\]*\t\[wx\]" } } */
+/* { dg-final { scan-assembler "\tldr\tq" } } */
+/* { dg-final { scan-assembler "\tstr\tq" } } */
