[committed][nvptx] Set -misa=sm_35 by default

[Tom de Vries]

Hi,

The nvptx-as assembler verifies the ptx code using ptxas, if there's any
in the PATH.

The default in the nvptx port for -misa=sm_xx is sm_30, but the ptxas of the
latest cuda release (11.1) no longer supports sm_30.

Consequently we cannot build gcc against that release (although we should
still be able to build without any cuda release).

Fix this by setting -misa=sm_35 by default.

Tested check-gcc on nvptx.

Tested libgomp on x86_64-linux with nvpx accelerator.

Both build against cuda 9.1.

Committed to trunk.

Thanks,
- Tom

[nvptx] Set -misa=sm_35 by default

gcc/ChangeLog:

2020-10-09  Tom de Vries  <tdevr...@suse.de>

        PR target/97348
        * config/nvptx/nvptx.h (ASM_SPEC): Also pass -m to nvptx-as if
        default is used.
        * config/nvptx/nvptx.opt (misa): Init with PTX_ISA_SM35.

---
 gcc/config/nvptx/nvptx.h   | 5 ++++-
 gcc/config/nvptx/nvptx.opt | 3 ++-
 2 files changed, 6 insertions(+), 2 deletions(-)

diff --git a/gcc/config/nvptx/nvptx.h b/gcc/config/nvptx/nvptx.h
index 6ebcc760771..17fe157058c 100644
--- a/gcc/config/nvptx/nvptx.h
+++ b/gcc/config/nvptx/nvptx.h
@@ -29,7 +29,10 @@
 
 #define STARTFILE_SPEC "%{mmainkernel:crt0.o}"
 
-#define ASM_SPEC "%{misa=*:-m %*}"
+/* Default needs to be in sync with default for misa in nvptx.opt.
+   We add a default here to work around a hard-coded sm_30 default in
+   nvptx-as.  */
+#define ASM_SPEC "%{misa=*:-m %*; :-m sm_35}"
 
 #define TARGET_CPU_CPP_BUILTINS()              \
   do                                           \
diff --git a/gcc/config/nvptx/nvptx.opt b/gcc/config/nvptx/nvptx.opt
index 75c3d54864e..d6910a96cf0 100644
--- a/gcc/config/nvptx/nvptx.opt
+++ b/gcc/config/nvptx/nvptx.opt
@@ -59,6 +59,7 @@ Enum(ptx_isa) String(sm_30) Value(PTX_ISA_SM30)
 EnumValue
 Enum(ptx_isa) String(sm_35) Value(PTX_ISA_SM35)
 
+; Default needs to be in sync with default in ASM_SPEC in nvptx.h.
 misa=
-Target RejectNegative ToLower Joined Enum(ptx_isa) Var(ptx_isa_option) 
Init(PTX_ISA_SM30)
+Target RejectNegative ToLower Joined Enum(ptx_isa) Var(ptx_isa_option) 
Init(PTX_ISA_SM35)
 Specify the version of the ptx ISA to use.