-Werror,-Wunused-but-set-variable

...which was apparently meant as a "Possible debugger breakpoint" in
DBG_UTIL-only sw_DebugRedline.  The obvious fix is to mark nDummy as volatile,
but increment of a volatile variable is deprecated, so replace those with reads
of the variable, but which triggered false loplugin:casttovoid so fix that too.

Change-Id: I07376e665caa4fd9befaba06d261a50df7a63a10
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/132237
Tested-by: Jenkins
Reviewed-by: Stephan Bergmann <sbergman@redhat.com>

compilerplugins/clang/casttovoid.cxx

@@ -202,6 +202,9 @@ public:
         if (var == nullptr) {
             return true;
         }
+        if (var->getType().isVolatileQualified()) {
+            return true;
+        }
         auto & usage = vars_[var->getCanonicalDecl()];
         if (!castToVoid_.empty() && castToVoid_.top().sub == expr) {
             usage.castToVoid.push_back(castToVoid_.top().cast);
@@ -506,6 +509,9 @@ private:
         if (var == nullptr) {
             return;
         }
+        if (var->getType().isVolatileQualified()) {
+            return;
+        }
         auto & usage = vars_[var->getCanonicalDecl()];
         if (usage.firstConsumption != nullptr) {
             return;

compilerplugins/clang/test/casttovoid.cxx

@@ -115,6 +115,8 @@ int main() {
     int n8 = 0;
     ASSERT(USE(USE(n8 == 0)));
     (void) n8;
+    int volatile n9 = 0;
+    (void) n9;
     return n1 // expected-note 8 {{first consumption is here [loplugin:casttovoid]}}
         + n2 // expected-note {{first consumption is here [loplugin:casttovoid]}}
         + n3;

sw/source/core/doc/docredln.cxx

@@ -69,13 +69,13 @@ using namespace com::sun::star;
         const SwRedlineTable& rTable = pDoc->getIDocumentRedlineAccess().GetRedlineTable();
         for( SwRedlineTable::size_type n = 0; n < rTable.size(); ++n )
         {
-            SwRedlineTable::size_type nDummy = 0;
+            volatile SwRedlineTable::size_type nDummy = 0;
             const SwRangeRedline* pCurrent = rTable[ n ];
             const SwRangeRedline* pNext = n+1 < rTable.size() ? rTable[ n+1 ] : nullptr;
             if( pCurrent == pNext )
-                ++nDummy;
+                (void) nDummy;
             if( n == nWatch )
-                ++nDummy; // Possible debugger breakpoint
+                (void) nDummy; // Possible debugger breakpoint
         }
     }