fix SIGFPE caused by integer division overflow sinteger_t.min / (-1) in constant folding

[MaskRay]

No description provided.

[WalterBright]

I'm not sure how integer division produces a floating point exception?

In any case, this needs a test case.

[MaskRay]

The Mod function already checks for integer division overflow but the Div function didn't, I just copied the code. See http://stackoverflow.com/questions/17176221/is-int-min-1-defined-behavior-in-c for details.

        if (n2 == -1 && !type.isunsigned())
        {
            // Check for int.min % -1
            if (n1 == 0xFFFFFFFF80000000UL && type.toBasetype().ty != Tint64)
            {
                e2.error("integer overflow: int.min % -1");
                n2 = 1;
            }
            else if (n1 == 0x8000000000000000L) // long.min % -1
            {
                e2.error("integer overflow: long.min % -1");
                n2 = 1;
            }
        }

You will get a SIGFPE doing LONG_MIN / (-1) on Linux x86_64,

% /usr/bin/dmd /tmp/a.d
[1]    10707 floating point exception (core dumped)  /usr/bin/dmd /tmp/a.d

[dlang-bot]

Fix	Bugzilla	Description
✗	4682	[CTFE] Run-time Vs Compile-time of int.min % -1

[MartinNowak]

SIGFPE is triggered on divide by zero as well and is used for any arithmetic errors.
The GNU C Library: Program Error Signals

[MartinNowak]

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