[x86] PR target/107548: Handle vec_select in STV.
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This patch enhances x86's STV pass to handle VEC_SELECT during general
scalar chain conversion, performing SImode scalar extraction from V4SI
and DImode scalar extraction from V2DI vector registers.
The motivating test case from bugzilla is:
typedef unsigned int v4si __attribute__((vector_size(16)));
unsigned int f (v4si a, v4si b)
{
a[0] += b[0];
return a[0] + a[1];
}
currently with -O2 -march=znver2 this generates:
vpextrd $1, %xmm0, %edx
vmovd %xmm0, %eax
addl %edx, %eax
vmovd %xmm1, %edx
addl %edx, %eax
ret
which performs three transfers from the vector unit to the scalar unit,
and performs the two additions there. With this patch, we now generate:
vmovdqa %xmm0, %xmm2
vpshufd $85, %xmm0, %xmm0
vpaddd %xmm0, %xmm2, %xmm0
vpaddd %xmm1, %xmm0, %xmm0
vmovd %xmm0, %eax
ret
which performs the two additions in the vector unit, and then transfers
the result to the scalar unit. Technically the (cheap) movdqa isn't
needed with better register allocation (or this could be cleaned up
during peephole2), but even so this transform is still a win.
This patch has been tested on x86_64-pc-linux-gnu with make bootstrap
and make -k check, both with and without --target_board=unix{-m32},
with no new failures. Ok for mainline?
2022-12-22 Roger Sayle <roger@nextmovesoftware.com>
gcc/ChangeLog
PR target/107548
* config/i386/i386-features.cc (scalar_chain::add_insn): The
operands of a VEC_SELECT don't need to added to the scalar chain.
(general_scalar_chain::compute_convert_gain) <case VEC_SELECT>:
Provide gains for performing STV on a VEC_SELECT.
(general_scalar_chain::convert_insn): Convert VEC_SELECT to pshufd,
psrldq or no-op.
(general_scalar_to_vector_candidate_p): Handle VEC_SELECT of a
single element from a vector register to a scalar register.
gcc/testsuite/ChangeLog
PR target/107548
* gcc.target/i386/pr107548-1.c: New test V4SI case.
* gcc.target/i386/pr107548-1.c: New test V2DI case.
Thanks in advance,
Roger
--
Comments
On Fri, Dec 23, 2022 at 12:19 AM Roger Sayle <roger@nextmovesoftware.com> wrote:
>
>
> This patch enhances x86's STV pass to handle VEC_SELECT during general
> scalar chain conversion, performing SImode scalar extraction from V4SI
> and DImode scalar extraction from V2DI vector registers.
>
> The motivating test case from bugzilla is:
>
> typedef unsigned int v4si __attribute__((vector_size(16)));
>
> unsigned int f (v4si a, v4si b)
> {
> a[0] += b[0];
> return a[0] + a[1];
> }
>
> currently with -O2 -march=znver2 this generates:
>
> vpextrd $1, %xmm0, %edx
> vmovd %xmm0, %eax
> addl %edx, %eax
> vmovd %xmm1, %edx
> addl %edx, %eax
> ret
>
> which performs three transfers from the vector unit to the scalar unit,
> and performs the two additions there. With this patch, we now generate:
>
> vmovdqa %xmm0, %xmm2
> vpshufd $85, %xmm0, %xmm0
> vpaddd %xmm0, %xmm2, %xmm0
> vpaddd %xmm1, %xmm0, %xmm0
> vmovd %xmm0, %eax
> ret
>
> which performs the two additions in the vector unit, and then transfers
> the result to the scalar unit. Technically the (cheap) movdqa isn't
> needed with better register allocation (or this could be cleaned up
> during peephole2), but even so this transform is still a win.
>
> This patch has been tested on x86_64-pc-linux-gnu with make bootstrap
> and make -k check, both with and without --target_board=unix{-m32},
> with no new failures. Ok for mainline?
>
>
> 2022-12-22 Roger Sayle <roger@nextmovesoftware.com>
>
> gcc/ChangeLog
> PR target/107548
> * config/i386/i386-features.cc (scalar_chain::add_insn): The
> operands of a VEC_SELECT don't need to added to the scalar chain.
> (general_scalar_chain::compute_convert_gain) <case VEC_SELECT>:
> Provide gains for performing STV on a VEC_SELECT.
> (general_scalar_chain::convert_insn): Convert VEC_SELECT to pshufd,
> psrldq or no-op.
> (general_scalar_to_vector_candidate_p): Handle VEC_SELECT of a
> single element from a vector register to a scalar register.
>
> gcc/testsuite/ChangeLog
> PR target/107548
> * gcc.target/i386/pr107548-1.c: New test V4SI case.
> * gcc.target/i386/pr107548-1.c: New test V2DI case.
LGTM.
Thanks,
Uros.
@@ -429,6 +429,11 @@ scalar_chain::add_insn (bitmap candidates, unsigned int insn_uid)
for (ref = DF_INSN_UID_DEFS (insn_uid); ref; ref = DF_REF_NEXT_LOC (ref))
if (!HARD_REGISTER_P (DF_REF_REG (ref)))
analyze_register_chain (candidates, ref);
+
+ /* The operand(s) of VEC_SELECT don't need to be converted/convertible. */
+ if (def_set && GET_CODE (SET_SRC (def_set)) == VEC_SELECT)
+ return;
+
for (ref = DF_INSN_UID_USES (insn_uid); ref; ref = DF_REF_NEXT_LOC (ref))
if (!DF_REF_REG_MEM_P (ref))
analyze_register_chain (candidates, ref);
@@ -629,6 +634,23 @@ general_scalar_chain::compute_convert_gain ()
}
break;
+ case VEC_SELECT:
+ if (XVECEXP (XEXP (src, 1), 0, 0) == const0_rtx)
+ {
+ // movd (4 bytes) replaced with movdqa (4 bytes).
+ if (!optimize_insn_for_size_p ())
+ igain += ix86_cost->sse_to_integer - ix86_cost->xmm_move;
+ }
+ else
+ {
+ // pshufd; movd replaced with pshufd.
+ if (optimize_insn_for_size_p ())
+ igain += COSTS_N_BYTES (4);
+ else
+ igain += ix86_cost->sse_to_integer;
+ }
+ break;
+
default:
gcc_unreachable ();
}
@@ -1167,6 +1189,24 @@ general_scalar_chain::convert_insn (rtx_insn *insn)
convert_op (&src, insn);
break;
+ case VEC_SELECT:
+ if (XVECEXP (XEXP (src, 1), 0, 0) == const0_rtx)
+ src = XEXP (src, 0);
+ else if (smode == DImode)
+ {
+ rtx tmp = gen_lowpart (V1TImode, XEXP (src, 0));
+ dst = gen_lowpart (V1TImode, dst);
+ src = gen_rtx_LSHIFTRT (V1TImode, tmp, GEN_INT (64));
+ }
+ else
+ {
+ rtx tmp = XVECEXP (XEXP (src, 1), 0, 0);
+ rtvec vec = gen_rtvec (4, tmp, tmp, tmp, tmp);
+ rtx par = gen_rtx_PARALLEL (VOIDmode, vec);
+ src = gen_rtx_VEC_SELECT (vmode, XEXP (src, 0), par);
+ }
+ break;
+
default:
gcc_unreachable ();
}
@@ -1917,6 +1957,16 @@ general_scalar_to_vector_candidate_p (rtx_insn *insn, enum machine_mode mode)
case CONST_INT:
return REG_P (dst);
+ case VEC_SELECT:
+ /* Excluding MEM_P (dst) avoids intefering with vpextr[dq]. */
+ return REG_P (dst)
+ && REG_P (XEXP (src, 0))
+ && GET_MODE (XEXP (src, 0)) == (mode == DImode ? V2DImode
+ : V4SImode)
+ && GET_CODE (XEXP (src, 1)) == PARALLEL
+ && XVECLEN (XEXP (src, 1), 0) == 1
+ && CONST_INT_P (XVECEXP (XEXP (src, 1), 0, 0));
+
default:
return false;
}
new file mode 100644
@@ -0,0 +1,25 @@
+/* { dg-do compile { target { ! ia32 } } } */
+/* { dg-options "-O2 -mstv -mno-stackrealign" } */
+typedef unsigned int v4si __attribute__((vector_size(16)));
+
+unsigned int foo1 (v4si a, v4si b)
+{
+ a[0] += b[0];
+ return a[0] + a[1];
+}
+
+unsigned int foo2 (v4si a, v4si b)
+{
+ a[0] += b[0];
+ return a[0] + a[2];
+}
+
+unsigned int foo3 (v4si a, v4si b)
+{
+ a[0] += b[0];
+ return a[0] + a[3];
+}
+
+/* { dg-final { scan-assembler-times "\tmovd\t" 3 } } */
+/* { dg-final { scan-assembler-times "paddd" 6 } } */
+/* { dg-final { scan-assembler-not "addl" } } */
new file mode 100644
@@ -0,0 +1,13 @@
+/* { dg-do compile { target { ! ia32 } } } */
+/* { dg-options "-O2 -mstv -mno-stackrealign" } */
+typedef unsigned long long v2di __attribute__((vector_size(16)));
+
+unsigned long long foo(v2di a, v2di b)
+{
+ a[0] += b[0];
+ return a[0] + a[1];
+}
+
+/* { dg-final { scan-assembler-not "\taddq\t" } } */
+/* { dg-final { scan-assembler-times "paddq" 2 } } */
+/* { dg-final { scan-assembler "psrldq" } } */