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* [gcc r10-10987] [nvptx] Add uniform_warp_check insn
@ 2022-09-14 10:09 Thomas Schwinge
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From: Thomas Schwinge @ 2022-09-14 10:09 UTC (permalink / raw)
To: gcc-cvs
https://gcc.gnu.org/g:3875b025a97ae667523bebf9f4cf157a8f5854ce
commit r10-10987-g3875b025a97ae667523bebf9f4cf157a8f5854ce
Author: Tom de Vries <tdevries@suse.de>
Date: Fri Jan 28 10:28:59 2022 +0100
[nvptx] Add uniform_warp_check insn
On a GT 1030, with driver version 470.94 and -mptx=3.1 I run into:
...
FAIL: libgomp.oacc-c/../libgomp.oacc-c-c++-common/parallel-dims.c \
-DACC_DEVICE_TYPE_nvidia=1 -DACC_MEM_SHARED=0 -foffload=nvptx-none \
-O2 execution test
...
which minimizes to the same test-case as listed in commit "[nvptx]
Update default ptx isa to 6.3".
The problem is again that the first diverging branch is not handled as such in
SASS, which causes problems with a subsequent shfl insn, but given that we
have -mptx=3.1 we can't use the bar.warp.sync insn.
Given that the default is now -mptx=6.3, and consequently -mptx=3.1 is of a
lesser importance, implement the next best thing: abort when detecting
non-convergence using this insn:
...
{ .reg.b32 act;
vote.ballot.b32 act,1;
.reg.pred uni;
setp.eq.b32 uni,act,0xffffffff;
@ !uni trap;
@ !uni exit;
}
...
Interestingly, the effect of this is that rather than aborting, the test-case
now passes.
Tested on x86_64 with nvptx accelerator.
gcc/ChangeLog:
2022-01-31 Tom de Vries <tdevries@suse.de>
* config/nvptx/nvptx.c (nvptx_single): Use nvptx_uniform_warp_check.
* config/nvptx/nvptx.md (define_c_enum "unspecv"): Add
UNSPECV_UNIFORM_WARP_CHECK.
(define_insn "nvptx_uniform_warp_check"): New define_insn.
(cherry picked from commit f32f74c2e8cef5fe37af6d4e8d7e8f6b4c8ae9a8)
Diff:
---
gcc/config/nvptx/nvptx.c | 22 ++++++++++++++++++----
gcc/config/nvptx/nvptx.md | 18 ++++++++++++++++++
2 files changed, 36 insertions(+), 4 deletions(-)
diff --git a/gcc/config/nvptx/nvptx.c b/gcc/config/nvptx/nvptx.c
index eec07fc3d13..0b67d544e48 100644
--- a/gcc/config/nvptx/nvptx.c
+++ b/gcc/config/nvptx/nvptx.c
@@ -4425,15 +4425,29 @@ nvptx_single (unsigned mask, basic_block from, basic_block to)
if (tail_branch)
{
label_insn = emit_label_before (label, before);
- if (TARGET_PTX_6_0 && mode == GOMP_DIM_VECTOR)
- warp_sync = emit_insn_after (gen_nvptx_warpsync (), label_insn);
+ if (mode == GOMP_DIM_VECTOR)
+ {
+ if (TARGET_PTX_6_0)
+ warp_sync = emit_insn_after (gen_nvptx_warpsync (),
+ label_insn);
+ else
+ warp_sync = emit_insn_after (gen_nvptx_uniform_warp_check (),
+ label_insn);
+ }
before = label_insn;
}
else
{
label_insn = emit_label_after (label, tail);
- if (TARGET_PTX_6_0 && mode == GOMP_DIM_VECTOR)
- warp_sync = emit_insn_after (gen_nvptx_warpsync (), label_insn);
+ if (mode == GOMP_DIM_VECTOR)
+ {
+ if (TARGET_PTX_6_0)
+ warp_sync = emit_insn_after (gen_nvptx_warpsync (),
+ label_insn);
+ else
+ warp_sync = emit_insn_after (gen_nvptx_uniform_warp_check (),
+ label_insn);
+ }
if ((mode == GOMP_DIM_VECTOR || mode == GOMP_DIM_WORKER)
&& CALL_P (tail) && find_reg_note (tail, REG_NORETURN, NULL))
emit_insn_after (gen_exit (), label_insn);
diff --git a/gcc/config/nvptx/nvptx.md b/gcc/config/nvptx/nvptx.md
index b2350ab0d2d..34062027312 100644
--- a/gcc/config/nvptx/nvptx.md
+++ b/gcc/config/nvptx/nvptx.md
@@ -56,6 +56,7 @@
UNSPECV_XCHG
UNSPECV_BARSYNC
UNSPECV_WARPSYNC
+ UNSPECV_UNIFORM_WARP_CHECK
UNSPECV_MEMBAR
UNSPECV_MEMBAR_CTA
UNSPECV_DIM_POS
@@ -1483,6 +1484,23 @@
"\\tbar.warp.sync\\t0xffffffff;"
[(set_attr "predicable" "false")])
+(define_insn "nvptx_uniform_warp_check"
+ [(unspec_volatile [(const_int 0)] UNSPECV_UNIFORM_WARP_CHECK)]
+ ""
+ {
+ output_asm_insn ("{", NULL);
+ output_asm_insn ("\\t" ".reg.b32" "\\t" "act;", NULL);
+ output_asm_insn ("\\t" "vote.ballot.b32" "\\t" "act,1;", NULL);
+ output_asm_insn ("\\t" ".reg.pred" "\\t" "uni;", NULL);
+ output_asm_insn ("\\t" "setp.eq.b32" "\\t" "uni,act,0xffffffff;",
+ NULL);
+ output_asm_insn ("@ !uni\\t" "trap;", NULL);
+ output_asm_insn ("@ !uni\\t" "exit;", NULL);
+ output_asm_insn ("}", NULL);
+ return "";
+ }
+ [(set_attr "predicable" "false")])
+
(define_expand "memory_barrier"
[(set (match_dup 0)
(unspec_volatile:BLK [(match_dup 0)] UNSPECV_MEMBAR))]
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