[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.
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@ -4631,15 +4631,29 @@ nvptx_single (unsigned mask, basic_block from, basic_block to)
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if (tail_branch)
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{
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label_insn = emit_label_before (label, before);
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if (TARGET_PTX_6_0 && mode == GOMP_DIM_VECTOR)
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warp_sync = emit_insn_after (gen_nvptx_warpsync (), label_insn);
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if (mode == GOMP_DIM_VECTOR)
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{
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if (TARGET_PTX_6_0)
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warp_sync = emit_insn_after (gen_nvptx_warpsync (),
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label_insn);
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else
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warp_sync = emit_insn_after (gen_nvptx_uniform_warp_check (),
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label_insn);
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}
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before = label_insn;
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}
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else
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{
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label_insn = emit_label_after (label, tail);
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if (TARGET_PTX_6_0 && mode == GOMP_DIM_VECTOR)
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warp_sync = emit_insn_after (gen_nvptx_warpsync (), label_insn);
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if (mode == GOMP_DIM_VECTOR)
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{
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if (TARGET_PTX_6_0)
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warp_sync = emit_insn_after (gen_nvptx_warpsync (),
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label_insn);
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else
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warp_sync = emit_insn_after (gen_nvptx_uniform_warp_check (),
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label_insn);
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}
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if ((mode == GOMP_DIM_VECTOR || mode == GOMP_DIM_WORKER)
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&& CALL_P (tail) && find_reg_note (tail, REG_NORETURN, NULL))
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emit_insn_after (gen_exit (), label_insn);
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@ -57,6 +57,7 @@
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UNSPECV_XCHG
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UNSPECV_BARSYNC
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UNSPECV_WARPSYNC
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UNSPECV_UNIFORM_WARP_CHECK
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UNSPECV_MEMBAR
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UNSPECV_MEMBAR_CTA
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UNSPECV_MEMBAR_GL
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@ -1985,6 +1986,23 @@
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"\\tbar.warp.sync\\t0xffffffff;"
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[(set_attr "predicable" "false")])
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(define_insn "nvptx_uniform_warp_check"
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[(unspec_volatile [(const_int 0)] UNSPECV_UNIFORM_WARP_CHECK)]
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""
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{
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output_asm_insn ("{", NULL);
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output_asm_insn ("\\t" ".reg.b32" "\\t" "act;", NULL);
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output_asm_insn ("\\t" "vote.ballot.b32" "\\t" "act,1;", NULL);
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output_asm_insn ("\\t" ".reg.pred" "\\t" "uni;", NULL);
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output_asm_insn ("\\t" "setp.eq.b32" "\\t" "uni,act,0xffffffff;",
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NULL);
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output_asm_insn ("@ !uni\\t" "trap;", NULL);
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output_asm_insn ("@ !uni\\t" "exit;", NULL);
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output_asm_insn ("}", NULL);
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return "";
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}
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[(set_attr "predicable" "false")])
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(define_expand "memory_barrier"
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[(set (match_dup 0)
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(unspec_volatile:BLK [(match_dup 0)] UNSPECV_MEMBAR))]
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