Patchwork [C++,Path] PR 38958

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Submitter Paolo Carlini
Date June 12, 2013, 6:40 p.m.
Message ID <51B8C0BB.4000201@oracle.com>
Download mbox | patch
Permalink /patch/250863/
State New
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Comments

Paolo Carlini - June 12, 2013, 6:40 p.m.
Hi,

On 06/12/2013 07:46 PM, Jason Merrill wrote:
> On 06/12/2013 01:37 PM, Paolo Carlini wrote:
>> Rewording: as the one line comment says, I only call non_reference at 
>> the outset when I know that either we'll end up producing the normal 
>> unused-variable warning or nothing at all.
> Oh, I see.  But that's a rather subtle difference; better to have 
> 'type' mean something consistent and leave the unused-but-set code 
> checking TREE_TYPE (decl).
Yeah. Earlier today I had something similar in my tree. I'm finishing 
testing the below then.

Thanks,
Paolo.
Jason Merrill - June 12, 2013, 7:49 p.m.
OK.

Jason

Patch

Index: cp/decl.c
===================================================================
--- cp/decl.c	(revision 200012)
+++ cp/decl.c	(working copy)
@@ -622,17 +622,20 @@  poplevel (int keep, int reverse, int functionbody)
 	   push_local_binding where the list of decls returned by
 	   getdecls is built.  */
 	decl = TREE_CODE (d) == TREE_LIST ? TREE_VALUE (d) : d;
+	// See through references for improved -Wunused-variable (PR 38958).
+	tree type = non_reference (TREE_TYPE (decl));
 	if (VAR_P (decl)
 	    && (! TREE_USED (decl) || !DECL_READ_P (decl))
 	    && ! DECL_IN_SYSTEM_HEADER (decl)
 	    && DECL_NAME (decl) && ! DECL_ARTIFICIAL (decl)
-	    && TREE_TYPE (decl) != error_mark_node
-	    && (!CLASS_TYPE_P (TREE_TYPE (decl))
-		|| !TYPE_HAS_NONTRIVIAL_DESTRUCTOR (TREE_TYPE (decl))))
+	    && type != error_mark_node
+	    && (!CLASS_TYPE_P (type)
+		|| !TYPE_HAS_NONTRIVIAL_DESTRUCTOR (type)))
 	  {
 	    if (! TREE_USED (decl))
 	      warning (OPT_Wunused_variable, "unused variable %q+D", decl);
 	    else if (DECL_CONTEXT (decl) == current_function_decl
+		     // For -Wunused-but-set-variable leave references alone.
 		     && TREE_CODE (TREE_TYPE (decl)) != REFERENCE_TYPE
 		     && errorcount == unused_but_set_errorcount)
 	      {
Index: testsuite/g++.dg/warn/Wunused-var-20.C
===================================================================
--- testsuite/g++.dg/warn/Wunused-var-20.C	(revision 0)
+++ testsuite/g++.dg/warn/Wunused-var-20.C	(working copy)
@@ -0,0 +1,19 @@ 
+// PR c++/38958
+// { dg-options "-Wunused" }
+
+volatile int g;
+
+struct Lock
+{
+  ~Lock() { g = 0; }
+};
+
+Lock AcquireLock() { return Lock(); }
+
+int main()
+{
+  const Lock& lock = AcquireLock();
+  g = 1;
+  g = 2;
+  g = 3;
+}