[Bug libgomp/83589] [nvptx] mode-transitions.c and private-variables.{c,f90} execution FAILs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=83589 --- Comment #1 from Tom de Vries --- Using the patch from PR83920 comment 3 and testing libgomp.oacc-c/c.exp makes the libgomp.oacc-c/c.exp failures of this PR go away. So, this might be a duplicate.
[Bug libgomp/83589] [nvptx] mode-transitions.c and private-variables.{c,f90} execution FAILs at GOMP_NVPTX_JIT=-O0
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=83589
--- Comment #2 from Tom de Vries ---
I've minimized mode-transitions.c to:
...
#define n 32
int
main (void)
{
int arr_a[n];
#pragma acc parallel copyout(arr_a) num_gangs(1) num_workers(1)
vector_length(32)
{
#pragma acc loop vector
for (int m = 0; m < 32; m++)
;
#pragma acc loop vector
for (int m = 0; m < 32; m++)
arr_a[m] = 0;
}
}
...
and the ptx to:
...
.version 3.1
.target sm_30
.address_size 64
.entry main$_omp_fn$0 (.param .u64 %in_ar0);
.entry main$_omp_fn$0 (.param .u64 %in_ar0)
{
.reg .u64 %ar0;
ld.param.u64 %ar0,[%in_ar0];
.reg .pred %r36;
{
.reg .u32 %x;
mov.u32 %x,%tid.x;
setp.ne.u32 %r36,%x,0;
}
.reg .u64 %r26;
mov.u64 %r26,%ar0;
@ %r36 bra $L5;
$L5:
{
.reg .u32 %r32;
.reg .u32 %r33;
mov.b64 {%r32,%r33},%r26;
shfl.idx.b32 %r32,%r32,0,31;
shfl.idx.b32 %r33,%r33,0,31;
mov.b64 %r26,{%r32,%r33};
}
ld.u64 %r26,[%r26];
@ %r36 bra $L6;
st.u32 [%r26],0;
$L6:
ret;
}
...
Either removing:
- the broad cast bit, which is an identity operation, or
- the redundant branch to $L5
make the test pass.
This looks like another nvidia driver problem (with driver version 384.111).
[Bug libgomp/83589] [nvptx] mode-transitions.c and private-variables.{c,f90} execution FAILs at GOMP_NVPTX_JIT=-O0
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=83589
--- Comment #3 from Tom de Vries ---
(In reply to Tom de Vries from comment #2)
> This looks like another nvidia driver problem (with driver version 384.111).
Confirmed.
The empty branch
> @ %r36 bra $L5;
> $L5:
is translated into:
...
/*0128*/ @P0 BRA `(.L_1);
.L_1:
...
so, no sync after the branch (or ssy before the branch).
Consequently, when executing the shfl.idx a bit later:
...
/*0158*/ SHFL.IDX PT, R0, R0, RZ, 0x1f;
/*0168*/ SHFL.IDX PT, R2, R2, RZ, 0x1f;
...
we are in divergent mode and get undefined results.
Inserting some sort of nop in the branched-around part:
...
@ %r36 bra $L5;
{
.reg .u32 %nop_src;
.reg .u32 %nop_dst;
mov.u32 %nop_dst, %nop_src;
}
$L5:
...
makes the test pass, because then we generate:
...
/*0128*/ SSY `(.L_1);
/*0130*/ @P0 SYNC (*"TARGET= .L_1 "*);
/*0138*/ SYNC (*"TARGET= .L_1 "*);
.L_1:
...
[Bug libgomp/83589] [nvptx] mode-transitions.c and private-variables.{c,f90} execution FAILs at GOMP_NVPTX_JIT=-O0
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=83589
--- Comment #4 from Tom de Vries ---
Using this rudimentary workaround, I got the failing tests of this PR passing
again:
...
diff --git a/gcc/config/nvptx/nvptx.c b/gcc/config/nvptx/nvptx.c
index afb0e4dd185..3ac28b3d903 100644
--- a/gcc/config/nvptx/nvptx.c
+++ b/gcc/config/nvptx/nvptx.c
@@ -78,6 +78,7 @@
#include "target-def.h"
#define WORKAROUND_PTXJIT_BUG 1
+#define WORKAROUND_PTXJIT_BUG_2 1
/* The various PTX memory areas an object might reside in. */
enum nvptx_data_area
@@ -4431,6 +4432,12 @@ nvptx_reorg (void)
if (TARGET_UNIFORM_SIMT)
nvptx_reorg_uniform_simt ();
+#if WORKAROUND_PTXJIT_BUG_2
+ for (rtx_insn *insn = get_insns (); insn; insn = NEXT_INSN (insn))
+if (LABEL_P (insn))
+ emit_insn_before (gen_fake_nop (), insn);
+#endif
+
regstat_free_n_sets_and_refs ();
df_finish_pass (true);
diff --git a/gcc/config/nvptx/nvptx.md b/gcc/config/nvptx/nvptx.md
index f9c087b6d22..909484c329a 100644
--- a/gcc/config/nvptx/nvptx.md
+++ b/gcc/config/nvptx/nvptx.md
@@ -994,6 +994,15 @@
""
"")
+(define_insn "fake_nop"
+ [(const_int 1)]
+ ""
+ "{
+ .reg .u32 %%nop_src;
+ .reg .u32 %%nop_dst;
+ mov.u32 %%nop_dst, %%nop_src;
+ }")
+
(define_insn "return"
[(return)]
""
...
[Bug libgomp/83589] [nvptx] mode-transitions.c and private-variables.{c,f90} execution FAILs at GOMP_NVPTX_JIT=-O0
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=83589 --- Comment #5 from Tom de Vries --- Using the workaround, I get pretty good results: ... Running /home/vries/openacc/trunk/source-gcc/libgomp/testsuite/libgomp.c/c.exp ... FAIL: libgomp.c/target-32.c (test for excess errors) FAIL: libgomp.c/target-33.c execution test FAIL: libgomp.c/target-34.c execution test FAIL: libgomp.c/target-link-1.c (test for excess errors) FAIL: libgomp.c/thread-limit-2.c (test for excess errors) Running /home/vries/openacc/trunk/source-gcc/libgomp/testsuite/libgomp.c++/c++.exp ... Running /home/vries/openacc/trunk/source-gcc/libgomp/testsuite/libgomp.fortran/fortran.exp ... FAIL: libgomp.fortran/target2.f90 -O0 execution test FAIL: libgomp.fortran/target2.f90 -O1 execution test Running /home/vries/openacc/trunk/source-gcc/libgomp/testsuite/libgomp.graphite/graphite.exp ... Running /home/vries/openacc/trunk/source-gcc/libgomp/testsuite/libgomp.hsa.c/c.exp ... Running /home/vries/openacc/trunk/source-gcc/libgomp/testsuite/libgomp.oacc-c/c.exp ... Running /home/vries/openacc/trunk/source-gcc/libgomp/testsuite/libgomp.oacc-c++/c++.exp ... Running /home/vries/openacc/trunk/source-gcc/libgomp/testsuite/libgomp.oacc-fortran/fortran.exp ... === libgomp Summary === # of expected passes8731 # of unexpected failures7 # of unresolved testcases 3 # of unsupported tests 240 ...
[Bug libgomp/83589] [nvptx] mode-transitions.c and private-variables.{c,f90} execution FAILs at GOMP_NVPTX_JIT=-O0
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=83589
--- Comment #6 from Jakub Jelinek ---
(In reply to Tom de Vries from comment #4)
> Using this rudimentary workaround, I got the failing tests of this PR
> passing again:
> ...
> diff --git a/gcc/config/nvptx/nvptx.c b/gcc/config/nvptx/nvptx.c
> index afb0e4dd185..3ac28b3d903 100644
> --- a/gcc/config/nvptx/nvptx.c
> +++ b/gcc/config/nvptx/nvptx.c
> @@ -78,6 +78,7 @@
> #include "target-def.h"
>
> #define WORKAROUND_PTXJIT_BUG 1
> +#define WORKAROUND_PTXJIT_BUG_2 1
>
> /* The various PTX memory areas an object might reside in. */
> enum nvptx_data_area
> @@ -4431,6 +4432,12 @@ nvptx_reorg (void)
>if (TARGET_UNIFORM_SIMT)
> nvptx_reorg_uniform_simt ();
>
> +#if WORKAROUND_PTXJIT_BUG_2
> + for (rtx_insn *insn = get_insns (); insn; insn = NEXT_INSN (insn))
> +if (LABEL_P (insn))
> + emit_insn_before (gen_fake_nop (), insn);
> +#endif
> +
>regstat_free_n_sets_and_refs ();
>
>df_finish_pass (true);
> diff --git a/gcc/config/nvptx/nvptx.md b/gcc/config/nvptx/nvptx.md
> index f9c087b6d22..909484c329a 100644
> --- a/gcc/config/nvptx/nvptx.md
> +++ b/gcc/config/nvptx/nvptx.md
> @@ -994,6 +994,15 @@
>""
>"")
>
> +(define_insn "fake_nop"
> + [(const_int 1)]
> + ""
> + "{
> + .reg .u32 %%nop_src;
> + .reg .u32 %%nop_dst;
> + mov.u32 %%nop_dst, %%nop_src;
> + }")
> +
> (define_insn "return"
>[(return)]
>""
> ...
Shouldn't it be sufficient to emit this only for JUMP_Ps that jump to
immediately following LABEL_Ps (without intervening non-note insns)?
[Bug libgomp/83589] [nvptx] mode-transitions.c and private-variables.{c,f90} execution FAILs at GOMP_NVPTX_JIT=-O0
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=83589 --- Comment #7 from Tom de Vries --- (In reply to Jakub Jelinek from comment #6) > (In reply to Tom de Vries from comment #4) > > Using this rudimentary workaround, I got the failing tests of this PR > > passing again: > Shouldn't it be sufficient to emit this only for JUMP_Ps that jump to > immediately following LABEL_Ps (without intervening non-note insns)? The emitted code actually looks like: ... @ %r36 bra $L5; // join x; // fork x; $L5: ... so we'll have to skip over this pattern as well (given that the join are fork are individual insns) . But indeed, this is a rudimentary workaround, not a minimal one.
[Bug libgomp/83589] [nvptx] mode-transitions.c and private-variables.{c,f90} execution FAILs at GOMP_NVPTX_JIT=-O0
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=83589 --- Comment #8 from Tom de Vries --- Created attachment 43209 --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=43209&action=edit Patch inserting fake_nop only in case of branch-around-nothing
