> James Greenhalgh wrote:
> On Mon, Apr 27, 2015 at 05:57:26PM +0100, Wilco Dijkstra wrote:
> > > James Greenhalgh wrote:
> > > On Mon, Apr 27, 2015 at 02:42:36PM +0100, Wilco Dijkstra wrote:
> > > > > -----Original Message-----
> > > > > From: Wilco Dijkstra [mailto:wdijk...@arm.com]
> > > > > Sent: 03 March 2015 16:19
> > > > > To: GCC Patches
> > > > > Subject: [PATCH][AArch64] Use conditional negate for abs expansion
> > > > >
> > > > > Expand abs into a compare and conditional negate. This is the most
> > > > > obvious expansion,
> > > enables
> > > > > merging of the comparison into ALU instructions and is faster on all
> > > > > implementations.
> > > > > Bootstrapped & regression tested.
> > > > >
> > > > > int f(int x) { return abs (x + 1); }
> > > > >
> > > > > Before:
> > > > > add w0, w0, 1
> > > > > sxtw x0, w0
> > > > > eor x1, x0, x0, asr 63
> > > > > sub x1, x1, x0, asr 63
> > > > > mov x0, x1
> > > > > ret
> > > > >
> > > > > After:
> > > > > adds w0, w0, 1
> > > > > csneg w0, w0, w0, pl
> > > > > ret
> > > > >
> > > > > ChangeLog:
> > > > >
> > > > > 2015-03-03 Wilco Dijkstra <wdijk...@arm.com>
> > > > >
> > > > > * gcc/config/aarch64/aarch64.md (absdi2): optimize abs
> > > > > expansion.
> > > > > (csneg3<mode>_insn): enable expansion of pattern.
> > > > > * gcc/testsuite/gcc.target/aarch64/abs_1.c (abs64): update test
> > > > > for new abs expansion. (abs64_in_dreg): likewise.
> > >
> > >
> > > This looks like it breaks support for abs in a D register (for example
> > > at the end of a loop, or extracted from Neon Intrinsics, etc).
> > >
> > > e.g. (totally contrived...)
> > >
> > > int64x1_t
> > > abs_max (int64x2_t x, int64_t *wb)
> > > {
> > > int64_t y = vgetq_lane_s64 (x, 0);
> > > if (y < 0)
> > > y = -y;
> > > return vdup_n_s64 (y);
> > > }
> > >
> > > Which currently generates:
> > >
> > > abs_max:
> > > abs d0, d0
> > > ret
> > >
> > > I suppose we don't need to worry too much about that (and the current
> > > implementation doesn't seem to catch it reliably anyway), but it would be
> > > good if we could keep the support - even if it is rarely used.
> >
> > Well it may be possible to write a peephole for this rare case, but I hope
> > people would use a vabs if that's what they wanted...
>
> OK, I've seen some of the pain of our current abs expansion code, so I
> suppose that we want to get the common case right first, rather
> than be too concerned about contrived corner cases.
>
> This patch is OK.
Jiong, could you check this in please?
Wilco
---
gcc/config/aarch64/aarch64.md | 33 +++++++-------------------------
gcc/testsuite/gcc.target/aarch64/abs_1.c | 5 ++---
2 files changed, 9 insertions(+), 29 deletions(-)
diff --git a/gcc/config/aarch64/aarch64.md b/gcc/config/aarch64/aarch64.md
index 1f4169e..46b7a63 100644
--- a/gcc/config/aarch64/aarch64.md
+++ b/gcc/config/aarch64/aarch64.md
@@ -2172,35 +2172,16 @@
[(set_attr "type" "alu_ext")]
)
-(define_insn_and_split "absdi2"
- [(set (match_operand:DI 0 "register_operand" "=&r,w")
- (abs:DI (match_operand:DI 1 "register_operand" "r,w")))]
+(define_expand "abs<mode>2"
+ [(match_operand:GPI 0 "register_operand" "")
+ (match_operand:GPI 1 "register_operand" "")]
""
- "@
- #
- abs\\t%d0, %d1"
- "reload_completed
- && GP_REGNUM_P (REGNO (operands[0]))
- && GP_REGNUM_P (REGNO (operands[1]))"
- [(const_int 0)]
{
- emit_insn (gen_rtx_SET (VOIDmode, operands[0],
- gen_rtx_XOR (DImode,
- gen_rtx_ASHIFTRT (DImode,
- operands[1],
- GEN_INT (63)),
- operands[1])));
- emit_insn (gen_rtx_SET (VOIDmode,
- operands[0],
- gen_rtx_MINUS (DImode,
- operands[0],
- gen_rtx_ASHIFTRT (DImode,
- operands[1],
- GEN_INT (63)))));
+ rtx ccreg = aarch64_gen_compare_reg (LT, operands[1], const0_rtx);
+ rtx x = gen_rtx_LT (VOIDmode, ccreg, const0_rtx);
+ emit_insn (gen_csneg3<mode>_insn (operands[0], x, operands[1],
operands[1]));
DONE;
}
- [(set_attr "type" "alu_sreg")
- (set_attr "simd" "no,yes")]
)
(define_insn "neg<mode>2"
@@ -2879,7 +2860,7 @@
[(set_attr "type" "csel")]
)
-(define_insn "*csneg3<mode>_insn"
+(define_insn "csneg3<mode>_insn"
[(set (match_operand:GPI 0 "register_operand" "=r")
(if_then_else:GPI
(match_operand 1 "aarch64_comparison_operation" "")
diff --git a/gcc/testsuite/gcc.target/aarch64/abs_1.c
b/gcc/testsuite/gcc.target/aarch64/abs_1.c
index 938bc84..11f1095 100644
--- a/gcc/testsuite/gcc.target/aarch64/abs_1.c
+++ b/gcc/testsuite/gcc.target/aarch64/abs_1.c
@@ -7,15 +7,14 @@ extern void abort (void);
long long
abs64 (long long a)
{
- /* { dg-final { scan-assembler "eor\t" } } */
- /* { dg-final { scan-assembler "sub\t" } } */
+ /* { dg-final { scan-assembler "csneg\t" } } */
return llabs (a);
}
long long
abs64_in_dreg (long long a)
{
- /* { dg-final { scan-assembler "abs\td\[0-9\]+, d\[0-9\]+" } } */
+ /* { dg-final { scan-assembler "csneg\t" } } */
register long long x asm ("d8") = a;
register long long y asm ("d9");
asm volatile ("" : : "w" (x));
--
1.9.1
