[nvptx, testsuite] Fix gcc.target/nvptx/alias-*.c on sm_80

When running test-cases gcc.target/nvptx/alias-*.c on target board
nvptx-none-run/-misa=sm_80 we run into fails because the test-cases add
-mptx=6.3, which doesn't support sm_80.

Fix this by only adding -mptx=6.3 if necessary, and simplify the test-cases by
using ptx_alias feature abstractions:
...
/* { dg-do run { target runtime_ptx_alias } } */
/* { dg-add-options ptx_alias } */
...

Tested on nvptx.

gcc/testsuite/ChangeLog:

2022-04-01  Tom de Vries  <tdevries@suse.de>

	* gcc.target/nvptx/nvptx.exp
	(check_effective_target_runtime_ptx_isa_version_6_3): Rename and
	generalize to ...
	(check_effective_target_runtime_ptx_isa_version_at_least): .. this.
	(check_effective_target_default_ptx_isa_version_at_least)
	(check_effective_target_runtime_ptx_alias, add_options_for_ptx_alias):
	New proc.
	* gcc.target/nvptx/alias-1.c: Use "target runtime_ptx_alias" and
	"dg-add-options ptx_alias".
	* gcc.target/nvptx/alias-2.c: Same.
	* gcc.target/nvptx/alias-3.c: Same.
	* gcc.target/nvptx/alias-4.c: Same.

gcc/testsuite/gcc.target/nvptx/alias-1.c

@@ -1,6 +1,7 @@
 /* { dg-do link } */
-/* { dg-do run { target runtime_ptx_isa_version_6_3 } } */
-/* { dg-options "-save-temps -malias -mptx=6.3" } */
+/* { dg-do run { target runtime_ptx_alias } } */
+/* { dg-options "-save-temps" } */
+/* { dg-add-options ptx_alias } */
 
 int v;
 

gcc/testsuite/gcc.target/nvptx/alias-2.c

@@ -1,6 +1,7 @@
 /* { dg-do link } */
-/* { dg-do run { target runtime_ptx_isa_version_6_3 } } */
-/* { dg-options "-save-temps -malias -mptx=6.3 -O2" } */
+/* { dg-do run { target runtime_ptx_alias } } */
+/* { dg-options "-save-temps -O2" } */
+/* { dg-add-options ptx_alias } */
 
 #include "alias-1.c"
 

gcc/testsuite/gcc.target/nvptx/alias-3.c

@@ -1,6 +1,7 @@
 /* { dg-do link } */
-/* { dg-do run { target runtime_ptx_isa_version_6_3 } } */
-/* { dg-options "-save-temps -malias -mptx=6.3" } */
+/* { dg-do run { target runtime_ptx_alias } } */
+/* { dg-options "-save-temps" } */
+/* { dg-add-options ptx_alias } */
 
 /* Copy of alias-1.c, with static __f and f.  */
 

gcc/testsuite/gcc.target/nvptx/alias-4.c

@@ -1,6 +1,7 @@
 /* { dg-do link } */
-/* { dg-do run { target runtime_ptx_isa_version_6_3 } } */
-/* { dg-options "-save-temps -malias -mptx=6.3 -O2" } */
+/* { dg-do run { target runtime_ptx_alias } } */
+/* { dg-options "-save-temps -O2" } */
+/* { dg-add-options ptx_alias } */
 
 #include "alias-3.c"
 

gcc/testsuite/gcc.target/nvptx/nvptx.exp

@@ -25,11 +25,65 @@ if ![istarget nvptx*-*-*] then {
 # Load support procs.
 load_lib gcc-dg.exp
 
-# Return 1 if code with -mptx=6.3 can be run.
-proc check_effective_target_runtime_ptx_isa_version_6_3 { args } {
-    return [check_runtime run_ptx_isa_6_3 {
+# Return 1 if code by default compiles for at least PTX ISA version
+# major.minor.
+proc check_effective_target_default_ptx_isa_version_at_least { major minor } {
+    set name default_ptx_isa_version_at_least_${major}_${minor}
+
+    set supported_p \
+	[concat \
+	     "((__PTX_ISA_VERSION_MAJOR__ == $major" \
+	     "  && __PTX_ISA_VERSION_MINOR__ >= $minor)" \
+	     " || (__PTX_ISA_VERSION_MAJOR__ > $major))"]
+
+    set src \
+	[list \
+	     "#if $supported_p" \
+	     "#else" \
+	     "#error unsupported" \
+	     "#endif"]
+    set src [join $src "\n"]
+    
+    set res [check_no_compiler_messages $name assembly $src ""]
+
+    return $res
+}
+
+# Return 1 if code with PTX ISA version major.minor or higher can be run.
+proc check_effective_target_runtime_ptx_isa_version_at_least { major minor } {
+    set name runtime_ptx_isa_version_${major}_${minor}
+
+    set default \
+	[check_effective_target_default_ptx_isa_version_at_least \
+	     ${major} ${minor}]
+
+    if { $default } {
+	set flag ""
+    } else {
+	set flag "-mptx=$major.$minor"
+    }
+
+    set res [check_runtime $name {
 	int main (void) { return 0; }
-    } "-mptx=6.3"]
+    } $flag]
+
+    return $res
+}
+
+# Return 1 if runtime environment support the PTX ISA directive .alias.
+proc check_effective_target_runtime_ptx_alias { } {
+    return [check_effective_target_runtime_ptx_isa_version_at_least 6 3]
+}
+
+# Add options to enable using PTX ISA directive .alias.
+proc add_options_for_ptx_alias { flags } {
+    append flags " -malias"
+
+    if { ![check_effective_target_default_ptx_isa_version_at_least 6 3] } {
+	append flags " -mptx=6.3"
+    }
+
+    return $flags
 }
 
 # If a testcase doesn't have special options, use these.