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Issue 5239 - optimizer misreports an used before set error
Summary: optimizer misreports an used before set error
Status: RESOLVED FIXED
Alias: None
Product: D
Classification: Unclassified
Component: dmd (show other issues)
Version: D2
Hardware: Other All
: P2 normal
Assignee: No Owner
URL:
Keywords: rejects-valid
Depends on:
Blocks:
 
Reported: 2010-11-18 22:34 UTC by Brad Roberts
Modified: 2011-08-03 17:13 UTC (History)
2 users (show)

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Description Brad Roberts 2010-11-18 22:34:20 UTC 
(an excerpt from runnable/interpret.d)

struct S { int x; }
template Compileable(int z) { bool OK=true;}

int goodfoo3()
{
   S[4] w = void; // uninitialized array of structs
   w[$-2].x = 217; // initialize one member
   return w[2].x; // line 8
}

$ dmd -c -O f.d
f.d(8): Error: variable w used before set

note: filed as d2, but might well exist on d1 as well.. untested
Comment 1 Brad Roberts 2011-08-03 00:06:43 UTC 
Part of the test case for bug 6293 triggers this bug when built with -O.  See runnable/xtet46.d, test6293().  The buggy part is hidden behind version(none).

class C6293 {
    C6293 token;
}
void f6293(in C6293[] a) pure {
    auto x0 = a[0].token;
    assert(x0 is a[0].token.token.token);
    assert(x0 is (&x0).token);
    version(none) {
        auto p1 = &x0 + 1;
        assert(x0 is (p1 - 1).token);
    }
    int c = 0;
    assert(x0 is a[c].token);
}
void test6293() {
    auto x = new C6293;
    x.token = x;
    f6293([x]);
}

See also:
  https://github.com/D-Programming-Language/dmd/pull/243