digitalmars.D.bugs - [Issue 6354] New: Optimizer bug on x86_64: Bitshift optimized out when foreach and scope(failure) are used
- d-bugmail puremagic.com (76/76) Jul 20 2011 http://d.puremagic.com/issues/show_bug.cgi?id=6354
- d-bugmail puremagic.com (10/10) Jul 31 2011 http://d.puremagic.com/issues/show_bug.cgi?id=6354
- d-bugmail puremagic.com (13/13) Nov 30 2011 http://d.puremagic.com/issues/show_bug.cgi?id=6354
- d-bugmail puremagic.com (11/11) Dec 27 2012 http://d.puremagic.com/issues/show_bug.cgi?id=6354
http://d.puremagic.com/issues/show_bug.cgi?id=6354 Summary: Optimizer bug on x86_64: Bitshift optimized out when foreach and scope(failure) are used Product: D Version: unspecified Platform: x86_64 OS/Version: Linux Status: NEW Severity: normal Priority: P2 Component: DMD AssignedTo: nobody puremagic.com ReportedBy: jmdavisProg gmx.com PDT --- Okay. This is a weird one, but it only happens on x86_64 when compiling with -O, so presumably it's a bug in the optmizer for x86_64. This code import std.stdio; ushort swapEndian(ushort val) { return ((val & 0xff00U) >> 8) | ((val & 0x00ffU) << 8); } void main() { foreach(j; 0 .. 2) { scope(failure) writefln("j: %s", j); ushort left = 0xffU; left <<= (ushort.sizeof - 1) * 8; ushort right = 0xffU; writefln("%s %s %s %s", swapEndian(left), right, swapEndian(right), left); assert(swapEndian(left) == right); } } does this: 255 65280 255 65280 j: 0 core.exception.AssertError q(25): Assertion failure ---------------- ---------------- Thee writefln at the bottom can be removed, but it helps show what's going on, since the correct output for this program would be 255 255 65280 65280 255 255 65280 65280 While the program does fail on the first iteration, removing the loop makes it so that it succeeds, so the foreach somehow helps cause the bug. Removing the scope(failure) also helps contribute, since removing _it_ gets rid of the bug. However, it fails regardless of whether it's a scope(failure), scope(success), or scope(exit). It also fails regardless of what's in the scope statement (e.g. it fails with scope(failure) int i;). You can also get rid of swapEndian and replace the call to it with its body and have the failure occur assert((((left & 0xff00U) >> 8) | ((left & 0x00ffU) << 8)) == right); so the function call isn't part of the problem (but it's easier to read with swapEndian in there, so I left in there). I can narrow it down to this at it still fails void main() { foreach(j; 0 .. 2) { scope(failure) int i = 0; ushort left = 0xffU; left <<= (ushort.sizeof - 1) * 8; assert((((left & 0xff00U) >> 8) | ((left & 0x00ffU) << 8)) == 0xffu); } } However, sometimes, some combination of changes in between those two states succeeds - probably depending on what the optimizer decides that it can optimize out. In any case, it seems that something is causing the optimizer to think that it can optimize out the bitshifts. And it's something that's going to cause test failures if the swapEndian stuff that I'm currently working on for Phobos gets merged in, so it would be nice if it could be fixed soon. -- Configure issuemail: http://d.puremagic.com/issues/userprefs.cgi?tab=email ------- You are receiving this mail because: -------
Jul 20 2011
http://d.puremagic.com/issues/show_bug.cgi?id=6354 Brad Roberts <braddr puremagic.com> changed: What |Removed |Added ---------------------------------------------------------------------------- Keywords| |wrong-code CC| |braddr puremagic.com Severity|normal |critical -- Configure issuemail: http://d.puremagic.com/issues/userprefs.cgi?tab=email ------- You are receiving this mail because: -------
Jul 31 2011
http://d.puremagic.com/issues/show_bug.cgi?id=6354 Walter Bright <bugzilla digitalmars.com> changed: What |Removed |Added ---------------------------------------------------------------------------- Status|NEW |RESOLVED CC| |bugzilla digitalmars.com Resolution| |FIXED 13:43:39 PST --- https://github.com/D-Programming-Language/dmd/commit/c468e89347d2f7306a64bfaa46e46fc3bf96b612 https://github.com/D-Programming-Language/dmd/commit/062351c39c6337eb09338a209d8e945c489852de -- Configure issuemail: http://d.puremagic.com/issues/userprefs.cgi?tab=email ------- You are receiving this mail because: -------
Nov 30 2011
http://d.puremagic.com/issues/show_bug.cgi?id=6354 Commits pushed to master at https://github.com/D-Programming-Language/phobos https://github.com/D-Programming-Language/phobos/commit/3bb400d4920a3d611fbe8b7b2500d815eb69d13e Decommented unittest that was blocked by bug 6354, which has since been fixed. https://github.com/D-Programming-Language/phobos/commit/901500b1605209638c4deadc38b2d7236be06880 Decommented unittest that was blocked by bug 6354, which has since been ... -- Configure issuemail: http://d.puremagic.com/issues/userprefs.cgi?tab=email ------- You are receiving this mail because: -------
Dec 27 2012