c89 does not perform array -> pointer promotion unless the array is an lvalue. This

is different than C99.  This fixes the rest of rdar://6095180.

llvm-svn: 54064

3 files changed, 34 insertions, 8 deletions

diff --git a/clang/lib/Sema/SemaExpr.cpp b/clang/lib/Sema/SemaExpr.cpp
index 8a4752ab1e6..9ffca0870c8 100644
--- a/clang/lib/Sema/SemaExpr.cpp
+++ b/clang/lib/Sema/SemaExpr.cpp
@@ -58,8 +58,16 @@ void Sema::DefaultFunctionArrayConversion(Expr *&E) {
   }
   if (Ty->isFunctionType())
     ImpCastExprToType(E, Context.getPointerType(Ty));
-  else if (Ty->isArrayType())
-    ImpCastExprToType(E, Context.getArrayDecayedType(Ty));
+  else if (Ty->isArrayType()) {
+    // In C90 mode, arrays only promote to pointers if the array expression is
+    // an lvalue.  The relevant legalese is C90 6.2.2.1p3: "an lvalue that has
+    // type 'array of type' is converted to an expression that has type 'pointer
+    // to type'...".  In C99 this was changed to: C99 6.3.2.1p3: "an expression
+    // that has type 'array of type' ...".  The relevant change is "an lvalue"
+    // (C90) to "an expression" (C99).
+    if (getLangOptions().C99 || E->isLvalue() == Expr::LV_Valid)
+      ImpCastExprToType(E, Context.getArrayDecayedType(Ty));
+  }
 }
 
 /// UsualUnaryConversions - Performs various conversions that are common to most
diff --git a/clang/test/Sema/expr-comma-c89.c b/clang/test/Sema/expr-comma-c89.c
new file mode 100644
index 00000000000..4949ee3a83f
--- /dev/null
+++ b/clang/test/Sema/expr-comma-c89.c
@@ -0,0 +1,18 @@
+// RUN: clang %s -fsyntax-only -verify -std=c99
+// rdar://6095180
+
+#include <assert.h>
+struct s { char c[17]; };
+extern struct s foo(void);
+
+struct s a, b, c;
+
+int A[sizeof((foo().c)) == 17 ? 1 : -1];
+int B[sizeof((a.c)) == 17 ? 1 : -1];
+
+
+// comma does array/function promotion in c99.
+int X[sizeof(0, (foo().c)) == sizeof(char*) ? 1 : -1];
+int Y[sizeof(0, (a,b).c) == sizeof(char*) ? 1 : -1];
+int Z[sizeof(0, (a=b).c) == sizeof(char*) ? 1 : -1];
+
diff --git a/clang/test/Sema/expr-comma.c b/clang/test/Sema/expr-comma.c
index 4949ee3a83f..849e8d5ae8b 100644
--- a/clang/test/Sema/expr-comma.c
+++ b/clang/test/Sema/expr-comma.c
@@ -1,4 +1,4 @@
-// RUN: clang %s -fsyntax-only -verify -std=c99
+// RUN: clang %s -fsyntax-only -verify -std=c89
 // rdar://6095180
 
 #include <assert.h>
@@ -11,8 +11,8 @@ int A[sizeof((foo().c)) == 17 ? 1 : -1];
 int B[sizeof((a.c)) == 17 ? 1 : -1];
 
 
-// comma does array/function promotion in c99.
-int X[sizeof(0, (foo().c)) == sizeof(char*) ? 1 : -1];
-int Y[sizeof(0, (a,b).c) == sizeof(char*) ? 1 : -1];
-int Z[sizeof(0, (a=b).c) == sizeof(char*) ? 1 : -1];
-
+// comma does not promote array/function in c90 unless they are lvalues.
+int W[sizeof(0, a.c) == sizeof(char*) ? 1 : -1];
+int X[sizeof(0, (foo().c)) == 17 ? 1 : -1];
+int Y[sizeof(0, (a,b).c) == 17 ? 1 : -1];
+int Z[sizeof(0, (a=b).c) == 17 ? 1 : -1];