Bug 4506 – Regression(2.034): -O flag breaks some recursive functions.

I wrote a function to count integer partitions. When compiled with dmd test.d, I get the correct result. Adding the -O flag makes the program return the incorrect result: import std.stdio; auto P(int n) { if (n < 0) return 0; if (n == 0) return 1; int c = 1; int r = 0; for (int k = 1; k <= n; ++k) { r += c * (P(n-k*(3*k-1)/2) + P(n-k*(3*k+1)/2)); c *= -1; } return r; } void main() { writeln(P(10)); } $ dmd test.d $ ./test 42 $ dmd -O test.d $ ./test 138 Unfortunately I haven't been able find a more minimal reproduction case. In particular, a basic recursive Fibonacci function works fine in both cases. Using dmd 2.047 on Mac OS X Snow Leopard.

This is very ugly. A reduced test case: void main() { int c = 1; for (int k = 0; k < 2; k++) { assert((k == 0 && c == 1) || (k == 1 && c == -1)); c *= -1; } }

Normal compilation: __Dmain comdat assume CS:__Dmain L0: enter 8,0 mov dword ptr -8[EBP],1 mov dword ptr -4[EBP],0 L12: cmp dword ptr -4[EBP],2 jge L42 cmp dword ptr -4[EBP],0 jne L24 cmp dword ptr -8[EBP],1 je L3A L24: cmp dword ptr -4[EBP],1 jne L30 cmp dword ptr -8[EBP],0FFFFFFFFh je L3A L30: mov EAX,4 call near ptr _D4test8__assertFiZv L3A: neg dword ptr -8[EBP] inc dword ptr -4[EBP] jmp short L12 L42: xor EAX,EAX leave ret __Dmain ends _D4test8__assertFiZv comdat assume CS:_D4test8__assertFiZv L0: enter 4,0 push EAX mov ECX,offset FLAT:_D4test12__ModuleInfoZ push ECX call near ptr __d_assertm leave ret With -O: __Dmain comdat assume CS:__Dmain L0: push EAX push EBX xor EBX,EBX push ESI mov ESI,1 LA: test EBX,EBX je L18 mov EAX,4 call near ptr _D4test8__assertFiZv L18: neg ESI inc EBX cmp EBX,2 jb LA pop ESI xor EAX,EAX pop EBX pop ECX ret __Dmain ends _D4test8__assertFiZv comdat assume CS:_D4test8__assertFiZv L0: push EAX mov ECX,offset FLAT:_D4test12__ModuleInfoZ push EAX push ECX call near ptr __d_assertm pop EAX ret

Great work, bearophile! This worked on 2.032, fails on 2.034 and later. Fails on D1 as well. This bug goes to the top of the list.

A one-line change in 2.034 which caused the regression. I think it's because c *= -1; becomes NEGATE c, which isn't a binary operation. Here's a patch which undoes the change. I'm not sure which bug it was attempting to fix. gother.c, line 480, inside chkprop(). if (d->Eoper == OPasm) /* OPasm elems ruin everything */ goto noprop; - if (OTassign(d->Eoper) && EBIN(d)) // if assignment elem + if (OTassign(d->Eoper)) // if assignment elem { elem *t = Elvalue(d); if (t->Eoper == OPvar)