[CGExprAgg] Don't create zero index GEP

With opaque pointers, we no longer need a zero-index GEP to get
the first element.

Author: nikic

clang/lib/CodeGen/CGExprAgg.cpp

@@ -448,11 +448,7 @@ AggExprEmitter::VisitCXXStdInitializerListExpr(CXXStdInitializerListExpr *E) {
   AggValueSlot Dest = EnsureSlot(E->getType());
   LValue DestLV = CGF.MakeAddrLValue(Dest.getAddress(), E->getType());
   LValue Start = CGF.EmitLValueForFieldInitialization(DestLV, *Field);
-  llvm::Value *Zero = llvm::ConstantInt::get(CGF.PtrDiffTy, 0);
-  llvm::Value *IdxStart[] = { Zero, Zero };
-  llvm::Value *ArrayStart = Builder.CreateInBoundsGEP(
-      ArrayPtr.getElementType(), ArrayPtr.emitRawPointer(CGF), IdxStart,
-      "arraystart");
+  llvm::Value *ArrayStart = ArrayPtr.emitRawPointer(CGF);
   CGF.EmitStoreThroughLValue(RValue::get(ArrayStart), Start);
   ++Field;
 
@@ -467,6 +463,7 @@ AggExprEmitter::VisitCXXStdInitializerListExpr(CXXStdInitializerListExpr *E) {
       Ctx.hasSameType(Field->getType()->getPointeeType(),
                       ArrayType->getElementType())) {
     // End pointer.
+    llvm::Value *Zero = llvm::ConstantInt::get(CGF.PtrDiffTy, 0);
     llvm::Value *IdxEnd[] = { Zero, Size };
     llvm::Value *ArrayEnd = Builder.CreateInBoundsGEP(
         ArrayPtr.getElementType(), ArrayPtr.emitRawPointer(CGF), IdxEnd,

clang/test/CodeGenCXX/cxx0x-initializer-stdinitializerlist-startend.cpp

@@ -49,7 +49,6 @@ void fn1(int i) {
   // CHECK-NEXT: store
   // init the list
   // CHECK-NEXT: getelementptr
-  // CHECK-NEXT: getelementptr inbounds [3 x i32], ptr
   // CHECK-NEXT: store ptr
   // CHECK-NEXT: getelementptr
   // CHECK-NEXT: getelementptr inbounds [3 x i32], ptr [[array]], i{{32|64}} 0, i{{32|64}} 3

clang/test/CodeGenCXX/cxx0x-initializer-stdinitializerlist.cpp

@@ -131,7 +131,6 @@ void fn1(int i) {
   // CHECK-NEXT: store
   // init the list
   // CHECK-NEXT: getelementptr
-  // CHECK-NEXT: getelementptr inbounds [3 x i32], ptr
   // CHECK-NEXT: store ptr
   // CHECK-NEXT: getelementptr
   // CHECK-NEXT: store i{{32|64}} 3