From a04a1538ee5e286e94e3374caf51ba1094d289b0 Mon Sep 17 00:00:00 2001
From: Eli Friedman <eli.friedman@gmail.com>
Date: Fri, 30 May 2008 19:58:50 +0000
Subject: [PATCH] Fix and enable generating general union initializers.
 Essentially, what this does is reconstruct the type for structs and arrays if
 the type wouldn't be compatible otherwise.

The assertion about packing in the struct type reconstruction code
sucks, but I don't see any obvious way to fix it.  Maybe we need a general
utility method to take a list of types and alignments and try to construct an
unpacked type if possible?



git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@51785 91177308-0d34-0410-b5e6-96231b3b80d8
---
 lib/CodeGen/CGExprConstant.cpp | 35 +++++++++++++++++++++++++---------
 test/CodeGen/union-init.c      | 31 ++++++++++++++++++++++++++++++
 2 files changed, 57 insertions(+), 9 deletions(-)
 create mode 100644 test/CodeGen/union-init.c

diff --git a/lib/CodeGen/CGExprConstant.cpp b/lib/CodeGen/CGExprConstant.cpp
index 1144cf1c91..4cb3c7bb2a 100644
--- a/lib/CodeGen/CGExprConstant.cpp
+++ b/lib/CodeGen/CGExprConstant.cpp
@@ -92,15 +92,26 @@ public:
 
     // Copy initializer elements.
     unsigned i = 0;
+    bool RewriteType = false;
     for (; i < NumInitableElts; ++i) {
       llvm::Constant *C = Visit(ILE->getInit(i));
+      RewriteType |= (C->getType() != ElemTy);
       Elts.push_back(C);
     }
-    
+
     // Initialize remaining array elements.
     for (; i < NumElements; ++i)
       Elts.push_back(llvm::Constant::getNullValue(ElemTy));
 
+    if (RewriteType) {
+      // FIXME: Try to avoid packing the array
+      std::vector<const llvm::Type*> Types;
+      for (unsigned i = 0; i < Elts.size(); ++i)
+        Types.push_back(Elts[i]->getType());
+      const llvm::StructType *SType = llvm::StructType::get(Types, true);
+      return llvm::ConstantStruct::get(SType, Elts);
+    }
+
     return llvm::ConstantArray::get(AType, Elts);    
   }
 
@@ -166,6 +177,7 @@ public:
     // Copy initializer elements. Skip padding fields.
     unsigned EltNo = 0;  // Element no in ILE
     int FieldNo = 0; // Field no in RecordDecl
+    bool RewriteType = false;
     while (EltNo < ILE->getNumInits() && FieldNo < RD->getNumMembers()) {
       FieldDecl* curField = RD->getMember(FieldNo);
       FieldNo++;
@@ -175,22 +187,27 @@ public:
       if (curField->isBitField()) {
         InsertBitfieldIntoStruct(Elts, curField, ILE->getInit(EltNo));
       } else {
-        Elts[CGM.getTypes().getLLVMFieldNo(curField)] =
-            Visit(ILE->getInit(EltNo));
+        unsigned FieldNo = CGM.getTypes().getLLVMFieldNo(curField);
+        llvm::Constant* C = Visit(ILE->getInit(EltNo));
+        RewriteType |= (C->getType() != Elts[FieldNo]->getType());
+        Elts[FieldNo] = C;
       }
       EltNo++;
     }
 
+    if (RewriteType) {
+      // FIXME: Make this work for non-packed structs
+      assert(SType->isPacked() && "Cannot recreate unpacked structs");
+      std::vector<const llvm::Type*> Types;
+      for (unsigned i = 0; i < Elts.size(); ++i)
+        Types.push_back(Elts[i]->getType());
+      SType = llvm::StructType::get(Types, true);
+    }
+
     return llvm::ConstantStruct::get(SType, Elts);
   }
 
   llvm::Constant *EmitUnionInitialization(InitListExpr *ILE) {
-    // FIXME: Need to make this work correctly for unions in structs/arrays
-    CGM.WarnUnsupported(ILE, "bitfield initialization");
-    return llvm::UndefValue::get(CGM.getTypes().ConvertType(ILE->getType()));
-
-    // Following is a partial implementation; it doesn't work correctly
-    // because the parent struct/arrays don't adapt their type yet, though
     RecordDecl *RD = ILE->getType()->getAsRecordType()->getDecl();
     const llvm::Type *Ty = ConvertType(ILE->getType());
 
diff --git a/test/CodeGen/union-init.c b/test/CodeGen/union-init.c
new file mode 100644
index 0000000000..9a515a72d9
--- /dev/null
+++ b/test/CodeGen/union-init.c
@@ -0,0 +1,31 @@
+// RUN: clang -emit-llvm < %s -o -
+
+// A nice and complicated initialization example with unions from Python
+typedef int Py_ssize_t;
+
+typedef union _gc_head {
+	struct {
+		union _gc_head *gc_next;
+		union _gc_head *gc_prev;
+		Py_ssize_t gc_refs;
+	} gc;
+	long double dummy;  /* force worst-case alignment */
+} PyGC_Head;
+
+struct gc_generation {
+	PyGC_Head head;
+	int threshold; /* collection threshold */
+	int count; /* count of allocations or collections of younger
+		      generations */
+};
+
+#define NUM_GENERATIONS 3
+#define GEN_HEAD(n) (&generations[n].head)
+
+/* linked lists of container objects */
+struct gc_generation generations[NUM_GENERATIONS] = {
+	/* PyGC_Head,				threshold,	count */
+	{{{GEN_HEAD(0), GEN_HEAD(0), 0}},	700,		0},
+	{{{GEN_HEAD(1), GEN_HEAD(1), 0}},	10,		0},
+	{{{GEN_HEAD(2), GEN_HEAD(2), 0}},	10,		0},
+};
-- 
2.40.0