On Fri, Oct 06, 2017 at 09:33:21AM +0000, Shalnov, Sergey wrote:
> Hi,
> GCC uses full 512-bit register in case of moving SF/DF value between two
> registers.
> The patch avoid 512-bit register usage if "-mprefer-avx256" option used.
>
> 2017-10-06 Sergey Shalnov <[email protected]>
>
> gcc/
> * config/i386/i386.md(*movsf_internal, *movdf_internal):
> Avoid 512-bit AVX modes for TARGET_PREFER_AVX256.
>
>From b96e657153b9aea24ff002e7e156ba12b2d443b5 Mon Sep 17 00:00:00 2001
From: Sergey Shalnov <[email protected]>
Date: Fri, 6 Oct 2017 10:45:40 +0300
Subject: [PATCH 1/1] Avoid 512-bit mode MOV for prefer-avx256 option
---
gcc/config/i386/i386.md | 10 ++++++----
1 file changed, 6 insertions(+), 4 deletions(-)
diff --git a/gcc/config/i386/i386.md b/gcc/config/i386/i386.md
index 99497a9..a6d7cca 100644
--- a/gcc/config/i386/i386.md
+++ b/gcc/config/i386/i386.md
@@ -3564,8 +3564,9 @@
/* movaps is one byte shorter for non-AVX targets. */
(eq_attr "alternative" "13,17")
- (cond [(ior (match_operand 0 "ext_sse_reg_operand")
- (match_operand 1 "ext_sse_reg_operand"))
+ (cond [(and (not (match_test "TARGET_PREFER_AVX256"))
+ (ior (match_operand 0 "ext_sse_reg_operand")
+ (match_operand 1 "ext_sse_reg_operand")))
(const_string "V8DF")
(ior (not (match_test "TARGET_SSE2"))
(match_test
"TARGET_SSE_PACKED_SINGLE_INSN_OPTIMAL"))
How does that work with -mprefer-avx256 -mavx512f -mno-avx512vl?
The constraints in these alternatives use v, and [SD]Fmode are included in
VALID_AVX512F_SCALAR_MODE and thus you can get e.g. %?mm23 among the
operands.
EVEX encoded VMOVAPD or VMOVAPS is AVX512F cpuid only with 512-bit operands,
with 128-bit/256-bit it is AVX512VL + AVX512F.
So, in both of the spots you've changed in this patch, but also in the
spots you've changed earlier, you need to use
TARGET_PREFER_AVX256 && TARGET_AVX512VL rather than just
TARGET_PREFER_AVX256, because without TARGET_AVX512VL it is not a matter
of preferring it, but a must. Unless we disable %xmm16+ registers
for TARGET_PREFER_AVX256 && !TARGET_AVX512VL code, but that would be weird:
an optimization preference would e.g. break people using %xmm16+ register
variables etc.
@@ -3739,8 +3740,9 @@
better to maintain the whole registers in single format
to avoid problems on using packed logical operations. */
(eq_attr "alternative" "6")
- (cond [(ior (match_operand 0 "ext_sse_reg_operand")
- (match_operand 1 "ext_sse_reg_operand"))
+ (cond [(and (not (match_test "TARGET_PREFER_AVX256"))
+ (ior (match_operand 0 "ext_sse_reg_operand")
+ (match_operand 1 "ext_sse_reg_operand")))
(const_string "V16SF")
(ior (match_test "TARGET_SSE_PARTIAL_REG_DEPENDENCY")
(match_test "TARGET_SSE_SPLIT_REGS"))
--
1.8.3.1
Jakub
