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[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.cc (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.
This commit is contained in:
Tom de Vries 2022-01-28 10:28:59 +01:00
parent bba61d403d
commit f32f74c2e8
2 changed files with 36 additions and 4 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

22
gcc/config/nvptx/nvptx.cc
View File

@ -4631,15 +4631,29 @@ 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);

18
gcc/config/nvptx/nvptx.md
View File

@ -57,6 +57,7 @@
UNSPECV_XCHG
UNSPECV_BARSYNC
UNSPECV_WARPSYNC
UNSPECV_UNIFORM_WARP_CHECK
UNSPECV_MEMBAR
UNSPECV_MEMBAR_CTA
UNSPECV_MEMBAR_GL
@ -1985,6 +1986,23 @@
"\\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))]