Bug 18315 – wrong code for `i > 0`

Found by kdevel who posted to D.learn: https://forum.dlang.org/post/[email protected] ---- void main () { int i = int.min; bool b = i > 0; assert(!b); /* fails */ } ----

Whoops. Accidentally hit "submit". This is what dmd generates for `i > 0`: ---- neg EAX shr EAX,01Fh ---- In D: `(-i) >> 31`. That code assumes that negation always flips the sign bit. But it doesn't for `int.min`. `-int.min` is `int.min` again.

Wow, this is really old. Tested all the way back to 2.040, still fails.

Also fails on MacosX.

Check cdcmp https://github.com/dlang/dmd/blob/62e615bf79f49ccd8c1ab45d6c38b956d2895c21/src/dmd/backend/cod4.c#L2066

Martin, the wrong code is for i > 0, not int.min > 0. int.min > 0 is folded to false: https://run.dlang.io/is/dvHi9a

Commits pushed to master at https://github.com/dlang/dmd https://github.com/dlang/dmd/commit/74904b6e43d0934f7fbcd2f966b04aaa58d4cde9 fix issue 18315 - wrong code for `i > 0` `SBB reg,0` is needed to make this work. There's nothing platform specific about it. Also add comments explaining how this works. https://github.com/dlang/dmd/commit/b4a86786619bcbbd52c9ecf2db4a75a5c3f52911 fixup! fix issue 18315 - wrong code for `i > 0` https://github.com/dlang/dmd/commit/4ccde911c8131dc170212f9a2f6d926ba7bdbe80 Merge pull request #7841 from aG0aep6G/18315 fix issue 18315 - wrong code for `i > 0`

*** Issue 18001 has been marked as a duplicate of this issue. ***