while loops

Note that neither the payload capture variable nor the error capture
variable require a stack allocation.

```zig
export fn entry() void {
    var c: anyerror!i32 = 1234;
    while (c) |hi| {} else |e| {}
}
```

```llvm
define void @entry() #2 !dbg !39 {
Entry:
  %c = alloca { i16, i32 }, align 4
  %0 = bitcast { i16, i32 }* %c to i8*, !dbg !52
  call void @llvm.memcpy.p0i8.p0i8.i64(i8* align 4 %0, i8* align 4 bitcast ({ i16, i32 }* @0 to i8*), i64 8, i1 false), !dbg !52
  call void @llvm.dbg.declare(metadata { i16, i32 }* %c, metadata !43, metadata !DIExpression()), !dbg !52
  br label %WhileCond, !dbg !53

WhileCond:                                        ; preds = %WhileBody, %Entry
  %1 = getelementptr inbounds { i16, i32 }, { i16, i32 }* %c, i32 0, i32 0, !dbg !54
  %2 = load i16, i16* %1, align 2, !dbg !54
  %3 = icmp ne i16 %2, 0, !dbg !54
  br i1 %3, label %WhileElse, label %WhileBody, !dbg !54

WhileBody:                                        ; preds = %WhileCond
  %4 = getelementptr inbounds { i16, i32 }, { i16, i32 }* %c, i32 0, i32 1, !dbg !53
  call void @llvm.dbg.declare(metadata i32* %4, metadata !50, metadata !DIExpression()), !dbg !53
  br label %WhileCond, !dbg !53

WhileElse:                                        ; preds = %WhileCond
  %5 = getelementptr inbounds { i16, i32 }, { i16, i32 }* %c, i32 0, i32 0, !dbg !55
  call void @llvm.dbg.declare(metadata i16* %5, metadata !51, metadata !DIExpression()), !dbg !55
  ret void, !dbg !56
}
```

1 files changed, 6 insertions, 8 deletions

diff --git a/src/codegen.cpp b/src/codegen.cpp
index b03068eb7d..84d5777530 100644
--- a/src/codegen.cpp
+++ b/src/codegen.cpp
@@ -4878,18 +4878,16 @@ static LLVMValueRef ir_render_test_err(CodeGen *g, IrExecutable *executable, IrI
 static LLVMValueRef ir_render_unwrap_err_code(CodeGen *g, IrExecutable *executable,
         IrInstructionUnwrapErrCode *instruction)
 {
-    ZigType *ptr_type = instruction->err_union->value.type;
+    ZigType *ptr_type = instruction->err_union_ptr->value.type;
     assert(ptr_type->id == ZigTypeIdPointer);
     ZigType *err_union_type = ptr_type->data.pointer.child_type;
     ZigType *payload_type = err_union_type->data.error_union.payload_type;
-    LLVMValueRef err_union_ptr = ir_llvm_value(g, instruction->err_union);
-    LLVMValueRef err_union_handle = get_handle_value(g, err_union_ptr, err_union_type, ptr_type);
-
-    if (type_has_bits(payload_type)) {
-        LLVMValueRef err_val_ptr = LLVMBuildStructGEP(g->builder, err_union_handle, err_union_err_index, "");
-        return gen_load_untyped(g, err_val_ptr, 0, false, "");
+    LLVMValueRef err_union_ptr = ir_llvm_value(g, instruction->err_union_ptr);
+    if (!type_has_bits(payload_type)) {
+        return err_union_ptr;
     } else {
-        return err_union_handle;
+        LLVMValueRef err_union_handle = get_handle_value(g, err_union_ptr, err_union_type, ptr_type);
+        return LLVMBuildStructGEP(g->builder, err_union_handle, err_union_err_index, "");
     }
 }