Index: lib/Sema/SemaStmt.cpp
===================================================================
--- lib/Sema/SemaStmt.cpp
+++ lib/Sema/SemaStmt.cpp
@@ -195,7 +195,7 @@
   if (isUnevaluatedContext())
     return;
 
-  SourceLocation ExprLoc = E->IgnoreParens()->getExprLoc();
+  SourceLocation ExprLoc = E->IgnoreParenImpCasts()->getExprLoc();
   // In most cases, we don't want to warn if the expression is written in a
   // macro body, or if the macro comes from a system header. If the offending
   // expression is a call to a function with the warn_unused_result attribute,
@@ -218,6 +218,16 @@
   if (isa<StmtExpr>(E) && Loc.isMacroID())
     return;
 
+  // Check if this is the UNREFERENCED_PARAMETER from the Microsoft headers.
+  // That macro is frequently used to suppress "unused parameter" warnings,
+  // but its implementation makes clang's -Wunused-value fire.  Prevent this.
+  if (getLangOpts().MSVCCompat && isa<ParenExpr>(E->IgnoreImpCasts()) &&
+      Loc.isMacroID()) {
+    SourceLocation SpellLoc = Loc;
+    if (findMacroSpelling(SpellLoc, "UNREFERENCED_PARAMETER"))
+      return;
+  }
+
   // Okay, we have an unused result.  Depending on what the base expression is,
   // we might want to make a more specific diagnostic.  Check for one of these
   // cases now.
Index: test/Sema/unused-expr.c
===================================================================
--- test/Sema/unused-expr.c
+++ test/Sema/unused-expr.c
@@ -1,4 +1,5 @@
 // RUN: %clang_cc1 -fsyntax-only -verify %s -Wno-unreachable-code
+// RUN: %clang_cc1 -DMS_COMPAT -fms-compatibility -fsyntax-only -verify %s -Wno-unreachable-code
 
 int foo(int X, int Y);
 
@@ -156,3 +157,13 @@
 #undef M5
 #undef M6
 #undef M7
+
+#define UNREFERENCED_PARAMETER(x) (x)
+
+void unused_parm(int a) {
+#ifdef MS_COMPAT
+  UNREFERENCED_PARAMETER(a);
+#else
+  UNREFERENCED_PARAMETER(a); // expected-warning {{expression result unused}}
+#endif
+}