[PATCH 2/2] nvptx: Prevent emitting duplicate declarations for '__nvptx_stacks', '__nvptx_uni'

[Thomas Schwinge <thomas@codesourcery.com>]

As I have reported to Nvidia in 2022-12-01 'NVIDIA Incident Report (3891704):
ptxas: Duplicate declaration error: "cannot be resolved by a '.static'"',
'ptxas' has an inscrutable error mode for duplicate declarations:

    ptxas softstack-decl-1.o, line 11; error   : '.extern' variable '__nvptx_stacks' cannot be resolved by a '.static'
    ptxas fatal   : Ptx assembly aborted due to errors
    nvptx-as: ptxas returned 255 exit status

    ptxas uniform-simt-decl-1.o, line 12; error   : '.extern' variable '__nvptx_uni' cannot be resolved by a '.static'
    ptxas fatal   : Ptx assembly aborted due to errors
    nvptx-as: ptxas returned 255 exit status

This is inscrutable, because (a) what is "cannot be resolved by a '.static'"
supposed to tell me (there is no '.static' in PTX?), and (b) why arent't
repeated declaration just verified to match the first, but otherwise a no-op
(like in other programming languages)?

        gcc/
        * config/nvptx/nvptx.cc (nvptx_assemble_undefined_decl): Notice
        '__nvptx_stacks', '__nvptx_uni' declarations.
        (nvptx_file_end): Don't emit duplicate declarations for those.
        gcc/testsuite/
        * gcc.target/nvptx/softstack-decl-1.c: Make 'dg-do assemble',
        adjust.
        * gcc.target/nvptx/uniform-simt-decl-1.c: Likewise.
---
 gcc/config/nvptx/nvptx.cc                          | 14 ++++++++++++--
 gcc/testsuite/gcc.target/nvptx/softstack-decl-1.c  |  8 ++++----
 .../gcc.target/nvptx/uniform-simt-decl-1.c         |  8 ++++----
 3 files changed, 20 insertions(+), 10 deletions(-)

diff --git a/gcc/config/nvptx/nvptx.cc b/gcc/config/nvptx/nvptx.cc
index 8e49dd9c647..b93a253ab31 100644
--- a/gcc/config/nvptx/nvptx.cc
+++ b/gcc/config/nvptx/nvptx.cc
@@ -180,9 +180,11 @@ static GTY(()) tree global_lock_var;

 /* True if any function references __nvptx_stacks.  */
 static bool need_softstack_decl;
+static bool have_softstack_decl;

 /* True if any function references __nvptx_uni.  */
 static bool need_unisimt_decl;
+static bool have_unisimt_decl;

 static int nvptx_mach_max_workers ();

@@ -2571,6 +2573,13 @@ nvptx_assemble_undefined_decl (FILE *file, const char *name, const_tree decl)
                             TREE_TYPE (decl), size ? tree_to_shwi (size) : 0,
                             DECL_ALIGN (decl), true);
   nvptx_assemble_decl_end ();
+
+  static tree softstack_id = get_identifier ("__nvptx_stacks");
+  static tree unisimt_id = get_identifier ("__nvptx_uni");
+  if (DECL_NAME (decl) == softstack_id)
+    have_softstack_decl = true;
+  else if (DECL_NAME (decl) == unisimt_id)
+    have_unisimt_decl = true;
 }

 /* Output a pattern for a move instruction.  */
@@ -6002,7 +6011,7 @@ nvptx_file_end (void)
     write_shared_buffer (asm_out_file, gang_private_shared_sym,
                         gang_private_shared_align, gang_private_shared_size);

-  if (need_softstack_decl)
+  if (need_softstack_decl && !have_softstack_decl)
     {
       write_var_marker (asm_out_file, false, true, "__nvptx_stacks");
       /* 32 is the maximum number of warps in a block.  Even though it's an
@@ -6011,7 +6020,8 @@ nvptx_file_end (void)
       fprintf (asm_out_file, ".extern .shared .u%d __nvptx_stacks[32];\n",
               POINTER_SIZE);
     }
-  if (need_unisimt_decl)
+
+  if (need_unisimt_decl && !have_unisimt_decl)
     {
       write_var_marker (asm_out_file, false, true, "__nvptx_uni");
       fprintf (asm_out_file, ".extern .shared .u32 __nvptx_uni[32];\n");
diff --git a/gcc/testsuite/gcc.target/nvptx/softstack-decl-1.c b/gcc/testsuite/gcc.target/nvptx/softstack-decl-1.c
index c502eacc1b3..2415f6adb1f 100644
--- a/gcc/testsuite/gcc.target/nvptx/softstack-decl-1.c
+++ b/gcc/testsuite/gcc.target/nvptx/softstack-decl-1.c
@@ -1,4 +1,4 @@
-/* { dg-do compile } */
+/* { dg-do assemble } */
 /* { dg-options {-save-temps -O0 -msoft-stack} } */

 extern void *__nvptx_stacks[32] __attribute__((shared,nocommon));
@@ -14,7 +14,7 @@ void *f()
   return stack_array[5];
 }

-/* The implicit (via 'need_softstack_decl') and explicit declarations of
-   '__nvptx_stacks' are both emitted:
-   { dg-final { scan-assembler-times {(?n)\.extern .* __nvptx_stacks\[32\];} 2 } }
+/* Of the implicit (via 'need_softstack_decl') and explicit declarations of
+   '__nvptx_stacks', only one is emitted:
+   { dg-final { scan-assembler-times {(?n)\.extern .* __nvptx_stacks\[32\];} 1 } }
 */
diff --git a/gcc/testsuite/gcc.target/nvptx/uniform-simt-decl-1.c b/gcc/testsuite/gcc.target/nvptx/uniform-simt-decl-1.c
index 486456ab243..5a975bdb269 100644
--- a/gcc/testsuite/gcc.target/nvptx/uniform-simt-decl-1.c
+++ b/gcc/testsuite/gcc.target/nvptx/uniform-simt-decl-1.c
@@ -1,4 +1,4 @@
-/* { dg-do compile } */
+/* { dg-do assemble } */
 /* { dg-options {-save-temps -O0 -muniform-simt} } */

 extern unsigned __nvptx_uni[32] __attribute__((shared,nocommon));
@@ -23,7 +23,7 @@ int f (void)
                                      MEMMODEL_RELAXED);
 }

-/* The implicit (via 'need_unisimt_decl') and explicit declarations of
-   '__nvptx_uni' are both emitted:
-   { dg-final { scan-assembler-times {(?n)\.extern .* __nvptx_uni\[32\];} 2 } }
+/* Of the implicit (via 'need_unisimt_decl') and explicit declarations of
+   '__nvptx_uni', only one is emitted:
+   { dg-final { scan-assembler-times {(?n)\.extern .* __nvptx_uni\[32\];} 1 } }
 */
--
2.25.1

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