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 <xuli1@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 --git a/gcc/match.pd b/gcc/match.pd
index 809c717bc86272ac85c863c9e5179f770c9b22c0..c851ac56e37c56bea3ebcda5ce5877961fb3c7a4 100644 (file)
--- 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 (file)
index 0000000..962bf09
--- /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 (file)
index 0000000..62a2ab6
--- /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" } } */