[debug] Reuse debug exprs generated in remap_ssa_name

When compiling gcc.dg/vla-1.c with -O3 -g, vla a and b in f1 are optimized
away, and f1 is cloned to a version f1.constprop with no parameters, eliminating
parameter i.  Debug info is generated to describe the sizes of a and b, but
that process generates debug expressions that are not reused.

Fix the duplication by saving and reusing the generated debug expressions in
remap_ssa_name.  Concretely: reuse D#7 here instead of generating D#8:
...
 __attribute__((noinline))
 f1.constprop ()
 {
   intD.6 iD.1935;

   <bb 3>
   # DEBUG D#10 s=> iD.1897
   # DEBUG iD.1935 => D#10

   <bb 2>
-  # DEBUG D#8 s=> iD.1935
   # DEBUG D#7 s=> iD.1935
   saved_stack.2_1 = __builtin_stack_save ();
   # DEBUG BEGIN_STMT
   # DEBUG D#6 => D#7 + 1
   # DEBUG D#5 => (long intD.8) D#6
   # DEBUG D#4 => D#5 + -1
   # DEBUG D.1937 => (sizetype) D#4
   # DEBUG a.0D.1942 => NULL
   # DEBUG BEGIN_STMT
-  # DEBUG D#3 => D#8 + 2
+  # DEBUG D#3 => D#7 + 2
   # DEBUG D#2 => (long intD.8) D#3
   # DEBUG D#1 => D#2 + -1
   # DEBUG D.1944 => (sizetype) D#1
   # DEBUG b.1D.1949 => NULL
...

Bootstrapped and reg-tested on x86_64.

2018-07-13  Tom de Vries  <tdevries@suse.de>

	* tree-inline.c (remap_ssa_name): Save and reuse debug exprs generated
	in remap_ssa_name.

	* gcc.dg/vla-1.c: Update.

From-SVN: r262628

gcc/ChangeLog

+2018-07-13  Tom de Vries  <tdevries@suse.de>
+
+	* tree-inline.c (remap_ssa_name): Save and reuse debug exprs generated
+	in remap_ssa_name.
+
 2018-07-13  Jackson Woodruff  <jackson.woodruff@arm.com>
 
 	* config/aarch64/aarch64.c (aarch64_operands_adjust_ok_for_ldpstp): Use

gcc/testsuite/ChangeLog

 2018-07-13  Tom de Vries  <tdevries@suse.de>
 
+	* gcc.dg/vla-1.c: Update.
+
+2018-07-13  Tom de Vries  <tdevries@suse.de>
+
 	* gcc.src/maintainers.exp: New file.
 
 2018-07-13  Kugan Vivekanandarajah  <kuganv@linaro.org>

gcc/testsuite/gcc.dg/vla-1.c

@@ -20,6 +20,7 @@ main ()
   return 0;
 }
 
-/* One debug source bind is generated for the parameter, and two to describe the
+/* One debug source bind is generated for the parameter, and one to describe the
    sizes of a and b.  */
-/* { dg-final { scan-tree-dump-times " s=> i" 3 "optimized" } } */
+/* { dg-final { scan-tree-dump-times " s=> i" 2 "optimized" } } */
+

gcc/tree-inline.c

@@ -214,12 +214,16 @@ remap_ssa_name (tree name, copy_body_data *id)
 	      processing_debug_stmt = -1;
 	      return name;
 	    }
+	  n = id->decl_map->get (val);
+	  if (n && TREE_CODE (*n) == DEBUG_EXPR_DECL)
+	    return *n;
 	  def_temp = gimple_build_debug_source_bind (vexpr, val, NULL);
 	  DECL_ARTIFICIAL (vexpr) = 1;
 	  TREE_TYPE (vexpr) = TREE_TYPE (name);
 	  SET_DECL_MODE (vexpr, DECL_MODE (SSA_NAME_VAR (name)));
 	  gsi = gsi_after_labels (single_succ (ENTRY_BLOCK_PTR_FOR_FN (cfun)));
 	  gsi_insert_before (&gsi, def_temp, GSI_SAME_STMT);
+	  insert_decl_map (id, val, vexpr);
 	  return vexpr;
 	}