https://gcc.gnu.org/g:4af8db3eca12b2db3753ce4b098cbd0ae32b4796
commit r15-4763-g4af8db3eca12b2db3753ce4b098cbd0ae32b4796
Author: xuli <xu...@eswincomputing.com>
Date: Tue Oct 22 09:48:03 2024 +0000
Match: Simplify (x != 0 ? x + ~0 : 0) to (x - x != 0).
When the imm operand op1=1 in the unsigned scalar sat_sub form2 below,
we can simplify (x != 0 ? x + ~0 : 0) to (x - x != 0), thereby eliminating
a branch instruction.This simplification also applies to signed integer.
Form2:
T __attribute__((noinline)) \
sat_u_sub_imm##IMM##_##T##_fmt_2 (T x) \
{ \
return x >= (T)IMM ? x - (T)IMM : 0; \
}
Take below form 2 as example:
DEF_SAT_U_SUB_IMM_FMT_2(uint8_t, 1)
Before this patch:
__attribute__((noinline))
uint8_t sat_u_sub_imm1_uint8_t_fmt_2 (uint8_t x)
{
uint8_t _1;
uint8_t _3;
<bb 2> [local count: 1073741824]:
if (x_2(D) != 0)
goto <bb 3>; [50.00%]
else
goto <bb 4>; [50.00%]
<bb 3> [local count: 536870912]:
_3 = x_2(D) + 255;
<bb 4> [local count: 1073741824]:
# _1 = PHI <x_2(D)(2), _3(3)>
return _1;
}
Assembly code:
sat_u_sub_imm1_uint8_t_fmt_2:
beq a0,zero,.L2
addiw a0,a0,-1
andi a0,a0,0xff
.L2:
ret
After this patch:
__attribute__((noinline))
uint8_t sat_u_sub_imm1_uint8_t_fmt_2 (uint8_t x)
{
_Bool _1;
unsigned char _2;
uint8_t _4;
<bb 2> [local count: 1073741824]:
_1 = x_3(D) != 0;
_2 = (unsigned char) _1;
_4 = x_3(D) - _2;
return _4;
}
Assembly code:
sat_u_sub_imm1_uint8_t_fmt_2:
snez a5,a0
subw a0,a0,a5
andi a0,a0,0xff
ret
The below test suites are passed for this patch:
1. The rv64gcv fully regression tests.
2. The x86 bootstrap tests.
3. The x86 fully regression tests.
Signed-off-by: Li Xu <xu...@eswincomputing.com>
gcc/ChangeLog:
* match.pd: Simplify (x != 0 ? x + ~0 : 0) to (x - x != 0).
gcc/testsuite/ChangeLog:
* gcc.dg/tree-ssa/phi-opt-44.c: New test.
* gcc.dg/tree-ssa/phi-opt-45.c: New test.
Diff:
---
gcc/match.pd | 10 ++++++++++
gcc/testsuite/gcc.dg/tree-ssa/phi-opt-44.c | 26 ++++++++++++++++++++++++++
gcc/testsuite/gcc.dg/tree-ssa/phi-opt-45.c | 26 ++++++++++++++++++++++++++
3 files changed, 62 insertions(+)
diff --git a/gcc/match.pd b/gcc/match.pd
index 809c717bc862..c851ac56e37c 100644
--- a/gcc/match.pd
+++ b/gcc/match.pd
@@ -3391,6 +3391,16 @@ DEFINE_INT_AND_FLOAT_ROUND_FN (RINT)
}
(if (wi::eq_p (sum, wi::uhwi (0, precision)))))))
+/* The boundary condition for case 10: IMM = 1:
+ SAT_U_SUB = X >= IMM ? (X - IMM) : 0.
+ simplify (X != 0 ? X + ~0 : 0) to (X - X != 0). */
+(simplify
+ (cond (ne@1 @0 integer_zerop)
+ (nop_convert? (plus (nop_convert? @0) integer_all_onesp))
+ integer_zerop)
+ (if (INTEGRAL_TYPE_P (type))
+ (minus @0 (convert @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;
diff --git a/gcc/testsuite/gcc.dg/tree-ssa/phi-opt-44.c
b/gcc/testsuite/gcc.dg/tree-ssa/phi-opt-44.c
new file mode 100644
index 000000000000..962bf0954f62
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/tree-ssa/phi-opt-44.c
@@ -0,0 +1,26 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -fdump-tree-phiopt1" } */
+
+#include <stdint.h>
+
+uint8_t f1 (uint8_t x)
+{
+ return x >= (uint8_t)1 ? x - (uint8_t)1 : 0;
+}
+
+uint16_t f2 (uint16_t x)
+{
+ return x >= (uint16_t)1 ? x - (uint16_t)1 : 0;
+}
+
+uint32_t f3 (uint32_t x)
+{
+ return x >= (uint32_t)1 ? x - (uint32_t)1 : 0;
+}
+
+uint64_t f4 (uint64_t x)
+{
+ return x >= (uint64_t)1 ? x - (uint64_t)1 : 0;
+}
+
+/* { dg-final { scan-tree-dump-not "goto" "phiopt1" } } */
diff --git a/gcc/testsuite/gcc.dg/tree-ssa/phi-opt-45.c
b/gcc/testsuite/gcc.dg/tree-ssa/phi-opt-45.c
new file mode 100644
index 000000000000..62a2ab631846
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/tree-ssa/phi-opt-45.c
@@ -0,0 +1,26 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -fdump-tree-phiopt1" } */
+
+#include <stdint.h>
+
+int8_t f1 (int8_t x)
+{
+ return x != 0 ? x - (int8_t)1 : 0;
+}
+
+int16_t f2 (int16_t x)
+{
+ return x != 0 ? x - (int16_t)1 : 0;
+}
+
+int32_t f3 (int32_t x)
+{
+ return x != 0 ? x - (int32_t)1 : 0;
+}
+
+int64_t f4 (int64_t x)
+{
+ return x != 0 ? x - (int64_t)1 : 0;
+}
+
+/* { dg-final { scan-tree-dump-not "goto" "phiopt1" } } */
