[v1,3/3] RISC-V: Split "(a & (1UL << bitno)) ? 0 : 1" to bext + xori
Commit Message
We avoid reassociating "(~(a >> BIT_NO)) & 1" into "((~a) >> BIT_NO) & 1"
by splitting it into a zero-extraction (bext) and an xori. This both
avoids burning a register on a temporary and generates a sequence that
clearly captures 'extract bit, then invert bit'.
This change improves the previously generated
srl a0,a0,a1
not a0,a0
andi a0,a0,1
into
bext a0,a0,a1
xori a0,a0,1
Signed-off-by: Philipp Tomsich <philipp.tomsich@vrull.eu>
gcc/ChangeLog:
* config/riscv/bitmanip.md: Add split covering
"(a & (1 << BIT_NO)) ? 0 : 1".
gcc/testsuite/ChangeLog:
* gcc.target/riscv/zbs-bext.c: Add testcases.
* gcc.target/riscv/zbs-bexti.c: Add testcases.
---
gcc/config/riscv/bitmanip.md | 13 +++++++++++++
gcc/testsuite/gcc.target/riscv/zbs-bext.c | 10 ++++++++--
gcc/testsuite/gcc.target/riscv/zbs-bexti.c | 10 ++++++++--
3 files changed, 29 insertions(+), 4 deletions(-)
@@ -365,3 +365,16 @@ (define_split
"TARGET_ZBS"
[(set (match_dup 0) (zero_extract:GPR (match_dup 1) (const_int 1) (match_dup 2)))
(set (match_dup 0) (plus:GPR (match_dup 0) (const_int -1)))])
+
+;; Split for "(a & (1 << BIT_NO)) ? 0 : 1":
+;; We avoid reassociating "(~(a >> BIT_NO)) & 1" into "((~a) >> BIT_NO) & 1",
+;; so we don't have to use a temporary. Instead we extract the bit and then
+;; invert bit 0 ("a ^ 1") only.
+(define_split
+ [(set (match_operand:X 0 "register_operand")
+ (and:X (not:X (lshiftrt:X (match_operand:X 1 "register_operand")
+ (subreg:QI (match_operand:X 2 "register_operand") 0)))
+ (const_int 1)))]
+ "TARGET_ZBS"
+ [(set (match_dup 0) (zero_extract:X (match_dup 1) (const_int 1) (match_dup 2)))
+ (set (match_dup 0) (xor:X (match_dup 0) (const_int 1)))])
@@ -23,16 +23,22 @@ long bext64_1(long a, char bitno)
long bext64_2(long a, char bitno)
{
- return (a & (1UL << bitno)) ? 0 : -1;
+ return (a & (1UL << bitno)) ? 0 : 1;
}
long bext64_3(long a, char bitno)
+{
+ return (a & (1UL << bitno)) ? 0 : -1;
+}
+
+long bext64_4(long a, char bitno)
{
return (a & (1UL << bitno)) ? -1 : 0;
}
/* { dg-final { scan-assembler-times "bexti\t" 1 } } */
-/* { dg-final { scan-assembler-times "bext\t" 4 } } */
+/* { dg-final { scan-assembler-times "bext\t" 5 } } */
+/* { dg-final { scan-assembler-times "xori\t|snez\t" 1 } } */
/* { dg-final { scan-assembler-times "addi\t" 1 } } */
/* { dg-final { scan-assembler-times "neg\t" 1 } } */
/* { dg-final { scan-assembler-not "andi" } } */
\ No newline at end of file
@@ -12,14 +12,20 @@ long bexti64_1(long a, char bitno)
long bexti64_2(long a, char bitno)
{
- return (a & (1UL << BIT_NO)) ? 0 : -1;
+ return (a & (1UL << BIT_NO)) ? 0 : 1;
}
long bexti64_3(long a, char bitno)
+{
+ return (a & (1UL << BIT_NO)) ? 0 : -1;
+}
+
+long bexti64_4(long a, char bitno)
{
return (a & (1UL << BIT_NO)) ? -1 : 0;
}
-/* { dg-final { scan-assembler-times "bexti\t" 3 } } */
+/* { dg-final { scan-assembler-times "bexti\t" 4 } } */
+/* { dg-final { scan-assembler-times "xori\t|snez\t" 1 } } */
/* { dg-final { scan-assembler-times "addi\t" 1 } } */
/* { dg-final { scan-assembler-times "neg\t" 1 } } */
\ No newline at end of file