[final] Handle compiler-generated asm insn

For the nvptx port, with -mptx-comment we have in pr53465.s:
...
        // #APP
// 9 "gcc/testsuite/gcc.c-torture/execute/pr53465.c" 1
        // Start: Added by -minit-regs=3:
        // #NO_APP
                mov.u32 %r26, 0;
        // #APP
// 9 "gcc/testsuite/gcc.c-torture/execute/pr53465.c" 1
        // End: Added by -minit-regs=3:
        // #NO_APP
...

The comments where generated using the compiler-generated equivalent of:
...
  asm ("// Comment");
...
but both the printed location and the NO_APP/APP are unnecessary for a
compiler-generated asm insn.

Fix this by:
- adding new flag ASM_INPUT_ARTIFICIAL_P
- in gen_comment:
  - setting ASM_INPUT_ARTIFICIAL_P to 1
  - setting ASM_INPUT_SOURCE_LOCATION to UNKNOWN_LOCATION,
- in final_scan_insn_1:
  - handling ASM_INPUT_SOURCE_LOCATION == UNKNOWN_LOCATION and
  ASM_INPUT_ARTIFICIAL_P
such what we simply get:
...
        // Start: Added by -minit-regs=3:
                mov.u32 %r26, 0;
        // End: Added by -minit-regs=3:
...

Tested on nvptx.

gcc/ChangeLog:

2022-02-21  Tom de Vries  <tdevries@suse.de>

	PR rtl-optimization/104596
	* rtl.h (struct rtx_def): Document use of jump flag in ASM_INPUT.
	(ASM_INPUT_ARTIFICIAL_P): New macro.
	* config/nvptx/nvptx.cc (gen_comment): Use gen_rtx_ASM_INPUT instead
	of gen_rtx_ASM_INPUT_loc.  Set ASM_INPUT_ARTIFICIAL_P.
	* final.cc (final_scan_insn_1): Handle
	ASM_INPUT_SOURCE_LOCATION == UNKNOWN_LOCATION and
	ASM_INPUT_ARTIFICIAL_P.

---
 gcc/config/nvptx/nvptx.cc |  5 +++--
 gcc/final.cc              | 18 ++++++++++++------
 gcc/rtl.h                 |  3 +++
 3 files changed, 18 insertions(+), 8 deletions(-)

diff --git a/gcc/config/nvptx/nvptx.cc b/gcc/config/nvptx/nvptx.cc
index 87efc23bd96a..93df3f309d18 100644
--- a/gcc/config/nvptx/nvptx.cc
+++ b/gcc/config/nvptx/nvptx.cc
@@ -5442,8 +5442,9 @@ gen_comment (const char *s)
   size_t len = strlen (ASM_COMMENT_START) + strlen (sep) + strlen (s) + 1;
   char *comment = (char *) alloca (len);
   snprintf (comment, len, "%s%s%s", ASM_COMMENT_START, sep, s);
-  return gen_rtx_ASM_INPUT_loc (VOIDmode, ggc_strdup (comment),
-				DECL_SOURCE_LOCATION (cfun->decl));
+  rtx asm_input = gen_rtx_ASM_INPUT (VOIDmode, ggc_strdup (comment));
+  ASM_INPUT_ARTIFICIAL_P (asm_input) = 1;
+  return asm_input;
 }
 
 /* Initialize all declared regs at function entry.
diff --git a/gcc/final.cc b/gcc/final.cc
index a9868861bd2c..fee512869482 100644
--- a/gcc/final.cc
+++ b/gcc/final.cc
@@ -2642,15 +2642,21 @@ final_scan_insn_1 (rtx_insn *insn, FILE *file, int optimize_p ATTRIBUTE_UNUSED,
 	    if (string[0])
 	      {
 		expanded_location loc;
+		bool unknown_loc_p
+		  = ASM_INPUT_SOURCE_LOCATION (body) == UNKNOWN_LOCATION;
 
-		app_enable ();
-		loc = expand_location (ASM_INPUT_SOURCE_LOCATION (body));
-		if (*loc.file && loc.line)
-		  fprintf (asm_out_file, "%s %i \"%s\" 1\n",
-			   ASM_COMMENT_START, loc.line, loc.file);
+		if (!ASM_INPUT_ARTIFICIAL_P (body))
+		  app_enable ();
+		if (!unknown_loc_p)
+		  {
+		    loc = expand_location (ASM_INPUT_SOURCE_LOCATION (body));
+		    if (*loc.file && loc.line)
+		      fprintf (asm_out_file, "%s %i \"%s\" 1\n",
+			       ASM_COMMENT_START, loc.line, loc.file);
+		  }
 		fprintf (asm_out_file, "\t%s\n", string);
 #if HAVE_AS_LINE_ZERO
-		if (*loc.file && loc.line)
+		if (!unknown_loc_p && *loc.file && loc.line)
 		  fprintf (asm_out_file, "%s 0 \"\" 2\n", ASM_COMMENT_START);
 #endif
 	      }
diff --git a/gcc/rtl.h b/gcc/rtl.h
index 9df2fab622e7..3d7cc2be45c4 100644
--- a/gcc/rtl.h
+++ b/gcc/rtl.h
@@ -325,6 +325,7 @@ struct GTY((desc("0"), tag("0"),
      1 in a VALUE is SP_BASED_VALUE_P in cselib.cc.
      1 in a SUBREG generated by LRA for reload insns.
      1 in a REG if this is a static chain register.
+     1 in an ASM_INPUT if it is compiler-generated.
      Dumped as "/j" in RTL dumps.  */
   unsigned int jump : 1;
   /* In a CODE_LABEL, part of the two-bit alternate entry field.
@@ -2592,6 +2593,8 @@ do {								        \
 #define ASM_OPERANDS_LABEL(RTX, N) XCVECEXP (RTX, 5, N, ASM_OPERANDS)
 #define ASM_OPERANDS_SOURCE_LOCATION(RTX) XCUINT (RTX, 6, ASM_OPERANDS)
 #define ASM_INPUT_SOURCE_LOCATION(RTX) XCUINT (RTX, 1, ASM_INPUT)
+#define ASM_INPUT_ARTIFICIAL_P(RTX) \
+  (RTL_FLAG_CHECK1 ("ASM_INPUT_ARTIFICIAL_P", (RTX), ASM_INPUT)->jump)
 
 /* 1 if RTX is a mem that is statically allocated in read-only memory.  */
 #define MEM_READONLY_P(RTX) \