r237839 - Evaluate union cast subexpressions when the cast value is unused

[Reid Kleckner]

Author: rnk
Date: Wed May 20 16:59:25 2015
New Revision: 237839

URL: http://llvm.org/viewvc/llvm-project?rev=237839&view=rev
Log:
Evaluate union cast subexpressions when the cast value is unused

Fixes PR23597.

Modified:
    cfe/trunk/lib/CodeGen/CGExprAgg.cpp
    cfe/trunk/test/CodeGen/exprs.c

Modified: cfe/trunk/lib/CodeGen/CGExprAgg.cpp
URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/lib/CodeGen/CGExprAgg.cpp?rev=237839&r1=237838&r2=237839&view=diff
==============================================================================
--- cfe/trunk/lib/CodeGen/CGExprAgg.cpp (original)
+++ cfe/trunk/lib/CodeGen/CGExprAgg.cpp Wed May 20 16:59:25 2015
@@ -584,7 +584,12 @@ void AggExprEmitter::VisitCastExpr(CastE
   }
       
   case CK_ToUnion: {
-    if (Dest.isIgnored()) break;
+    // Evaluate even if the destination is ignored.
+    if (Dest.isIgnored()) {
+      CGF.EmitAnyExpr(E->getSubExpr(), AggValueSlot::ignored(),
+                      /*ignoreResult=*/true);
+      break;
+    }
 
     // GCC union extension
     QualType Ty = E->getSubExpr()->getType();

Modified: cfe/trunk/test/CodeGen/exprs.c
URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/test/CodeGen/exprs.c?rev=237839&r1=237838&r2=237839&view=diff
==============================================================================
--- cfe/trunk/test/CodeGen/exprs.c (original)
+++ cfe/trunk/test/CodeGen/exprs.c Wed May 20 16:59:25 2015
@@ -184,3 +184,14 @@ void f17() {
   extfunc(x);
 // CHECK: add nsw i128 %{{.}}, -1
 }
+
+// PR23597: We should evaluate union cast operands even if the cast is unused.
+typedef union u {
+    int i;
+} strct;
+int returns_int(void);
+void f18() {
+  (strct)returns_int();
+}
+// CHECK-LABEL: define void @f18()
+// CHECK: call i32 @returns_int()