Bug 3681 – ICE(go.c): when function takes too long to optimize, only with -O.

against 1.055 might be a regression of issue 2773 compiling with optimization crashes the compiler. public final class A { private this() { int i =0; int j = i +1; i = j * 15; j = i * 59; i = j * 15; j = i * 59; i = j * 15; j = i * 59; i = j * 15; j = i * 59; i = j * 15; j = i * 59; i = j * 15; j = i * 59; i = j * 15; j = i * 59; i = j * 15; j = i * 59; i = j * 15; j = i * 59; i = j * 15; j = i * 59; i = j * 15; j = i * 59; i = j * 15; j = i * 59; i = j * 15; j = i * 59; i = j * 15; j = i * 59; i = j * 15; j = i * 59; i = j * 15; j = i * 59; i = j * 15; j = i * 59; i = j * 15; j = i * 59; i = j * 15; j = i * 59; i = j * 15; j = i * 59; i = j * 15; j = i * 59; i = j * 15; j = i * 59; i = j * 15; j = i * 59; i = j * 15; j = i * 59; i = j * 15; j = i * 59; i = j * 15; j = i * 59; i = j * 15; j = i * 59; i = j * 15; j = i * 59; i = j * 15; j = i * 59; i = j * 15; i = j * 15; j = i * 59; i = j * 15; j = i * 59; i = j * 15; j = i * 59; i = j * 15; j = i * 59; i = j * 15; j = i * 59; i = j * 15; j = i * 59; i = j * 15; j = i * 59; i = j * 15; j = i * 59; i = j * 15; j = i * 59; i = j * 15; j = i * 59; i = j * 15; j = i * 59; i = j * 15; j = i * 59; i = j * 15; j = i * 59; i = j * 15; j = i * 59; i = j * 15; j = i * 59; i = j * 15; j = i * 59; i = j * 15; j = i * 59; i = j * 15; j = i * 59; i = j * 15; j = i * 59; i = j * 15; j = i * 59; i = j * 15; j = i * 59; i = j * 15; j = i * 59; i = j * 15; j = i * 59; i = j * 15; j = i * 59; i = j * 15; j = i * 59; i = j * 15; j = i * 59; i = j * 15; j = i * 59; i = j * 15; j = i * 59; i = j * 15; j = i * 59; i = j * 15; j = i * 59; i = j * 15; j = i * 59; i = j * 15; j = i * 59; i = j * 15; j = i * 59; i = j * 15; j = i * 59; i = j * 15; j = i * 59; i = j * 15; j = i * 59; i = j * 15; j = i * 59; i = j * 15; j = i * 59; i = j * 15; j = i * 59; i = j * 15; j = i * 59; i = j * 15; j = i * 59; i = j * 15; j = i * 59; i = j * 15; j = i * 59; i = j * 15; j = i * 59; i = j * 15; j = i * 59; i = j * 15; j = i * 59; i = j * 15; j = i * 59; i = j * 15; j = i * 59; i = j * 15; j = i * 59; i = j * 15; j = i * 59; i = j * 15; j = i * 59; i = j * 15; j = i * 59; i = j * 15; j = i * 59; i = j * 15; j = i * 59; i = j * 15; j = i * 59; i = j * 15; j = i * 59; i = j * 15; j = i * 59; i = j * 15; j = i * 59; i = j * 15; j = i * 59; i = j * 15; j = i * 59; i = j * 15; j = i * 59; i = j * 15; j = i * 59; i = j * 15; j = i * 59; i = j * 15; j = i * 59; i = j * 15; j = i * 59; i = j * 15; j = i * 59; i = j * 15; j = i * 59; i = j * 15; j = i * 59; i = j * 15; j = i * 59; i = j * 15; j = i * 59; i = j * 15; j = i * 59; i = j * 15; j = i * 59; i = j * 15; j = i * 59; i = j * 15; j = i * 59; i = j * 15; j = i * 59; i = j * 15; j = i * 59; i = j * 15; j = i * 59; i = j * 15; j = i * 59; i = j * 15; j = i * 59; i = j * 15; j = i * 59; i = j * 15; j = i * 59; i = j * 15; j = i * 59; i = j * 15; j = i * 59; i = j * 15; j = i * 59; i = j * 15; j = i * 59; i = j * 15; j = i * 59; i = j * 15; j = i * 59; i = j * 15; j = i * 59; i = j * 15; j = i * 59; i = j * 15; j = i * 59; i = j * 15; j = i * 59; i = j * 15; j = i * 59; i = j * 15; j = i * 59; i = j * 15; j = i * 59; i = j * 15; j = i * 59; i = j * 15; j = i * 59; i = j * 15; j = i * 59; i = j * 15; j = i * 59; i = j * 15; j = i * 59; i = j * 15; j = i * 59; i = j * 15; j = i * 59; i = j * 15; j = i * 59; i = j * 15; j = i * 59; i = j * 15; j = i * 59; i = j * 15; j = i * 59; j = i * 59; i = j * 15; j = i * 59; i = j * 15; j = i * 59; i = j * 15; j = i * 59; i = j * 15; j = i * 59; i = j * 15; j = i * 59; i = j * 15; j = i * 59; i = j * 15; j = i * 59; i = j * 15; j = i * 59; i = j * 15; j = i * 59; } }

This also fails with DMD 2.039. Internal error: backend/go.c 244

(In reply to comment #0) > against 1.055 > > might be a regression of issue 2773 It isn't a regression. This is ancient -- it fails on DMD 0.175.

The problem is simply that the optimiser needs too much time. The optimiser loops for a maximum of 200 times, but to optimize this example requires 290 loops. On the line it's faulting on: - assert(++iter < 200); + assert(++iter < 290); However, there'll always be _some_ example where this happens. So a different approach is required. Maybe after 200 check that the number of elements is still decreasing on each pass through the loop; if it is, then just silently exit the loop without ICEing.

SVN Changeset: http://www.dsource.org/projects/dmd/changeset/376

CAUSE: This section of the optimiser can only remove one comma expression per pass. So, the limit should be set based on the depth of comma expressions. I don't know what the minimum iteration limit should be (the number of passes for performing all other optimisations) -- when setting it to 10, as in the code below, the test suite passes; a level of 5 is too low. Note that the total limit used to be set to 80, before it was increased to 200. I am certain that the 80 was caused by comma expressions. Need to run this through the DMC test suite, to see what the minimum iteration limit should be. ---------- PATCH: Add this function to go.c. Actually it needs to used in the fix for bug 4379, as well. So maybe it should go into another file, or appear in a header file. /* Return the maximum nesting of comma expressions in the elem tree. For example, (((a, b) + c),d) * (e,f) has comma depth 2. */ int commaDepth(elem *e) { if ( EBIN(e)) { int depth = (e->Eoper == OPcomma) ? 1 : 0; return depth + commaDepth(e->E1) + commaDepth(e->E2); } else if (EUNA(e)) return commaDepth(e->E1); return 0; } Then, go.c, optfunc(), around line 230: if (localgot) { // Initialize with: // localgot = OPgot; elem *e = el_long(TYnptr, 0); e->Eoper = OPgot; e = el_bin(OPeq, TYnptr, el_var(localgot), e); startblock->Belem = el_combine(e, startblock->Belem); } + // Each pass through the loop can reduce only one level of comma expression. + // The infinite loop check needs to take this into account. + int iterationLimit = 10; + for (b = startblock; b; b = b->Bnext) + { + if (!b->Belem) + continue; + int d = commaDepth(b->Belem); + if (d > iterationLimit) + iterationLimit = d; + } // Some functions can take enormous amounts of time to optimize. // We try to put a lid on it. starttime = clock(); do { //printf("iter = %d\n", iter); #if TX86 //assert(++iter < 80); /* infinite loop check */ - assert(++iter < 200); /* infinite loop + assert(++iter < iterationLimit); /* infinite loop check */ #else