llvm-gcc PaddingElement optimization results in valid fields not being copied

[llvmbot]

Bugzilla Link	1419
Resolution	FIXED
Resolved on	Feb 22, 2010 12:50
Version	unspecified
OS	Linux
Reporter	LLVM Bugzilla Contributor
CC	@lattner

Extended Description

Test case:

struct A {
short x;
long long :0;
};

struct B {
char a;
char b;
unsigned char i;
};

union X { struct A a; struct B b; };

int check(void) {
union X x, y;

y.b.i = 0xff;
x = y;
return (x.b.i == 0xff);
}

When compiled with -O2:

define i32 @​check() {
entry:
ret i32 0
}

It should return 1. This is because the X.i field is not
being copied by the aggregate copy, since it lives inside
the padding of struct A.

[lattner]

This looks serious. Devang, please consider reverting the optimization if necessary.

[llvmbot]

Fixed.
http://lists.cs.uiuc.edu/pipermail/llvm-commits/Week-of-Mon-20070514/049642.html