[Issue 21509] New: alloca and exceptions causes wrong code.

[d-bugmail at puremagic.com]

https://issues.dlang.org/show_bug.cgi?id=21509

          Issue ID: 21509
           Summary: alloca and exceptions causes wrong code.
           Product: D
           Version: D2
          Hardware: x86_64
                OS: Linux
            Status: NEW
          Severity: critical
          Priority: P1
         Component: dmd
          Assignee: nobody at puremagic.com
          Reporter: john.loughran.colvin at gmail.com

immutable ex = new Exception("fdsa");

void main() {
    import std.stdio : writeln;
    import core.stdc.stdlib : alloca;

    auto a = (cast(long*)alloca(8))[0..1];
    try {
        throw ex;
    } catch (Exception) { }
    a[0] = 3;

    writeln(a[0]); // 3
    writeln(*(a.ptr)); // something else, looks like an address of somewhere on
the stack?
}

LDC does the right thing and prints 3 both times.

For future readers: please be careful about closing this as "works for me",
because it's not a very stable bug. E.g. putting asserts in to check for 3 pass
if the writelns aren't there!

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