[PATCH] Avoid generating unused labels in genmatch.

["Roger Sayle" <roger@nextmovesoftware.com>]

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This patch is the second of two changes to genmatch that don't affect
the executable code, but reduce the amount of debugging information
generated in stage3 of a build, but adhering more closely to GNU style
guidelines.

This patch avoids generating "next_after_fail1:;" label statements
in genmatch, if this label is unused/never referenced as the target
of a goto.  Because jumps to these labels are always forwards, we
know at the point the label is emitted whether it is used or not.
Because a debugger may set a breakpoint these labels, this increase
the size of g{imple,eneric}-match.o in a stage3 build.  To save a
little extra space, I also shorten the label to "Lfail1:;" and only
increment the counter when necessary.  This reduces the size of
gimple-match.o by 58K on x86_64-pc-linux-gnu.

This patch has been tested on x86_64-pc-linux-gnu with make bootstrap
and make -k check with no new failures.  Ok for mainline?


2022-03-16  Roger Sayle  <roger@nextmovesoftware.com>

gcc/ChangeLog
	* gcc/genmatch.cc (fail_label_used): New global variable.
	(expr::gen_transform): Set fail_label_used whenever a goto
	FAIL_LABEL is generated.
	(dt_simplify::gen_1): Clear fail_label_used when generating
	a new (provisional) fail_label.  Set fail_label used whenever
	a goto fail_label is generated.  Avoid emitting fail_label:
	if fail_label_used is false, instead decrement fail_label_cnt.


Thanks in advance,
Roger
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diff --git a/gcc/genmatch.cc b/gcc/genmatch.cc
index 2eda730..4a61f4e 100644
--- a/gcc/genmatch.cc
+++ b/gcc/genmatch.cc
@@ -2356,6 +2356,8 @@ capture_info::walk_c_expr (c_expr *e)
 /* The current label failing the current matched pattern during
    code generation.  */
 static char *fail_label;
+/* Record that a reference/goto to the above label been generated.  */
+static bool fail_label_used;
 
 /* Code generation off the decision tree and the refered AST nodes.  */
 
@@ -2533,6 +2535,7 @@ expr::gen_transform (FILE *f, int indent, const char *dest, bool gimple,
       fprintf_indent (f, indent,
 		      "if (!_r%d) goto %s;\n",
 		      depth, fail_label);
+      fail_label_used = true;
       if (*opr == CONVERT_EXPR)
 	{
 	  indent -= 4;
@@ -2560,13 +2563,15 @@ expr::gen_transform (FILE *f, int indent, const char *dest, bool gimple,
       fprintf (f, ");\n");
       if (opr->kind != id_base::CODE)
 	{
-	  fprintf_indent (f, indent, "if (!_r%d)\n", depth);
-	  fprintf_indent (f, indent, "  goto %s;\n", fail_label);
+	  fprintf_indent (f, indent, "if (!_r%d) goto %s;\n",
+			  depth, fail_label);
+	  fail_label_used = true;
 	}
       if (force_leaf)
 	{
 	  fprintf_indent (f, indent, "if (EXPR_P (_r%d))\n", depth);
 	  fprintf_indent (f, indent, "  goto %s;\n", fail_label);
+	  fail_label_used = true;
 	}
       if (*opr == CONVERT_EXPR)
 	{
@@ -3285,8 +3290,9 @@ dt_simplify::gen_1 (FILE *f, int indent, bool gimple, operand *result)
 
   static unsigned fail_label_cnt;
   char local_fail_label[256];
-  snprintf (local_fail_label, 256, "next_after_fail%u", ++fail_label_cnt);
+  snprintf (local_fail_label, 256, "Lfail%u", ++fail_label_cnt);
   fail_label = local_fail_label;
+  fail_label_used = false;
 
   /* Analyze captures and perform early-outs on the incoming arguments
      that cover cases we cannot handle.  */
@@ -3301,6 +3307,7 @@ dt_simplify::gen_1 (FILE *f, int indent, bool gimple, operand *result)
 		fprintf_indent (f, indent,
 				"if (TREE_SIDE_EFFECTS (_p%d)) goto %s;\n",
 				i, fail_label);
+		fail_label_used = true;
 		if (verbose >= 1)
 		  warning_at (as_a <expr *> (s->match)->ops[i]->location,
 			      "forcing toplevel operand to have no "
@@ -3316,6 +3323,7 @@ dt_simplify::gen_1 (FILE *f, int indent, bool gimple, operand *result)
 		fprintf_indent (f, indent,
 				"if (TREE_SIDE_EFFECTS (captures[%d])) "
 				"goto %s;\n", i, fail_label);
+		fail_label_used = true;
 		if (verbose >= 1)
 		  warning_at (cinfo.info[i].c->location,
 			      "forcing captured operand to have no "
@@ -3358,7 +3366,12 @@ dt_simplify::gen_1 (FILE *f, int indent, bool gimple, operand *result)
     }
 
   if (s->kind == simplify::SIMPLIFY)
-    fprintf_indent (f, indent, "if (__builtin_expect (!dbg_cnt (match), 0)) goto %s;\n", fail_label);
+    {
+      fprintf_indent (f, indent,
+		      "if (__builtin_expect (!dbg_cnt (match), 0)) goto %s;\n",
+		      fail_label);
+      fail_label_used = true;
+    }
 
   fprintf_indent (f, indent, "if (__builtin_expect (dump_file && (dump_flags & TDF_FOLDING), 0)) "
 	   "fprintf (dump_file, \"%s ",
@@ -3430,9 +3443,12 @@ dt_simplify::gen_1 (FILE *f, int indent, bool gimple, operand *result)
 	      fprintf_indent (f, indent,
 			      "res_op->resimplify (lseq, valueize);\n");
 	      if (e->force_leaf)
-		fprintf_indent (f, indent,
-				"if (!maybe_push_res_to_seq (res_op, NULL)) "
-				"goto %s;\n", fail_label);
+		{
+		  fprintf_indent (f, indent,
+				  "if (!maybe_push_res_to_seq (res_op, NULL))"
+				  " goto %s;\n", fail_label);
+		  fail_label_used = true;
+		}
 	    }
 	}
       else if (result->type == operand::OP_CAPTURE
@@ -3488,9 +3504,12 @@ dt_simplify::gen_1 (FILE *f, int indent, bool gimple, operand *result)
 		  continue;
 		if (cinfo.info[i].result_use_count
 		    > cinfo.info[i].match_use_count)
-		  fprintf_indent (f, indent,
-				  "if (! tree_invariant_p (captures[%d])) "
-				  "goto %s;\n", i, fail_label);
+		  {
+		    fprintf_indent (f, indent,
+				    "if (! tree_invariant_p (captures[%d]))"
+				    " goto %s;\n", i, fail_label);
+		    fail_label_used = true;
+		  }
 	      }
 	  for (unsigned j = 0; j < e->ops.length (); ++j)
 	    {
@@ -3539,8 +3558,9 @@ dt_simplify::gen_1 (FILE *f, int indent, bool gimple, operand *result)
 		  fprintf (f, ");\n");
 		  if (!is_a <operator_id *> (opr))
 		    {
-		      fprintf_indent (f, indent, "if (!_r)\n");
-		      fprintf_indent (f, indent, "  goto %s;\n", fail_label);
+		      fprintf_indent (f, indent, "if (!_r) goto %s;\n",
+				      fail_label);
+		      fail_label_used = true;
 		    }
 		}
 	    }
@@ -3581,7 +3601,10 @@ dt_simplify::gen_1 (FILE *f, int indent, bool gimple, operand *result)
     }
   indent -= 2;
   fprintf_indent (f, indent, "}\n");
-  fprintf (f, "%s:;\n", fail_label);
+  if (fail_label_used)
+    fprintf (f, "%s:;\n", fail_label);
+  else
+    fail_label_cnt--;
   fail_label = NULL;
 }