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D.gnu - [Bug 187] New: Nested struct that has non-padded array does not

Date: Thu, 21 May 2015 11:06:05 +0100
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            Bug ID: 187
           Summary: Nested struct that has non-padded array does not
                    initialize fields correctly when compiled with
           Product: GDC
           Version: 4.9.x
          Hardware: x86_64
                OS: Linux
            Status: NEW
          Severity: normal
          Priority: Normal
         Component: gdc
          Assignee: ibuclaw gdcproject.org
          Reporter: liran weka.io

Reproducible on commit b022dd4cac195d85e9c3a6a37f2501a07ade455a from April 7th
on the 4.9 branch.

Consider the following code:
module test;
import std.stdio;

align(1) struct Unpadded {
    align(1) {
        uint unpaddedA;
        ushort unpaddedB;

struct StructWithUnpaddedArray {
    Unpadded[3] unpaddedArray;
    // If initializer differs than ubyte.init then it does get inititalized
    // Naturally, the "= ubyte.init" part is not required for the bug to
    ubyte wontInitialize = ubyte.init;

struct OuterStruct {
    StructWithUnpaddedArray interesting;

void prepareStack()
    byte[255] stackGarbage;
    foreach(i, ref b; stackGarbage) {
        b  = cast(byte)(-i);

void main()
    auto a = OuterStruct(StructWithUnpaddedArray());
    writefln("Value is %s . wontInitialize is %s ", a,
When compiled with optimization, the wontInitialize field ends up being 194,
instead of 0 as by the D spec.

This is the minimal code that I was able to get that reproduces.

example output:
bash-4.3# /opt/gdc/bin/gdc -ggdb -O -ogtest test.d && ./gtest
Value is OuterStruct(StructWithUnpaddedArray([Unpadded(0, 0), Unpadded(0, 0),
Unpadded(0, 0)], 194)) . wontInitialize is 194

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May 21 2015