digitalmars.D.bugs - [Issue 12164] New: Function returning ptrdiff_t.min in 64-bit returning 0 when -O is set.
- d-bugmail puremagic.com (49/49) Feb 14 2014 https://d.puremagic.com/issues/show_bug.cgi?id=12164
- d-bugmail puremagic.com (10/10) Feb 15 2014 https://d.puremagic.com/issues/show_bug.cgi?id=12164
- d-bugmail puremagic.com (13/13) Feb 16 2014 https://d.puremagic.com/issues/show_bug.cgi?id=12164
- d-bugmail puremagic.com (24/24) Mar 06 2014 https://d.puremagic.com/issues/show_bug.cgi?id=12164
- d-bugmail puremagic.com (13/15) Mar 09 2014 https://d.puremagic.com/issues/show_bug.cgi?id=12164
- d-bugmail puremagic.com (9/9) Mar 15 2014 https://d.puremagic.com/issues/show_bug.cgi?id=12164
- d-bugmail puremagic.com (9/16) Mar 15 2014 https://d.puremagic.com/issues/show_bug.cgi?id=12164
- d-bugmail puremagic.com (41/44) Mar 31 2014 https://d.puremagic.com/issues/show_bug.cgi?id=12164
- d-bugmail puremagic.com (16/16) Mar 31 2014 https://d.puremagic.com/issues/show_bug.cgi?id=12164
- d-bugmail puremagic.com (8/16) Mar 31 2014 https://d.puremagic.com/issues/show_bug.cgi?id=12164
https://d.puremagic.com/issues/show_bug.cgi?id=12164 Summary: Function returning ptrdiff_t.min in 64-bit returning 0 when -O is set. Product: D Version: D2 Platform: All OS/Version: All Status: NEW Keywords: wrong-code Severity: major Priority: P2 Component: DMD AssignedTo: nobody puremagic.com ReportedBy: opantm2+dbugs gmail.com The title isn't very descriptive, but perhaps the sample is more useful. Reduced from std.variant. Uncommenting the writeln, using -m32, commenting out the if(*rhsPA == *zis) return 0, or not passing in -O causes the problem to not occur. Otherwise compile the below with -O -m64 to have it occur. Sample: import std.stdio, std.exception, std.c.string; struct Foo { ubyte[32] store; this(A value) { memcpy(&store, &value, value.sizeof); } static ptrdiff_t compare(A* rhsPA, A* zis) { if (*rhsPA == *zis) return 0; //writeln("Returning min"); return ptrdiff_t.min; } bool opEquals(Foo rhs) const { auto zis = cast(A*)&store; auto rhsPA = cast(A*)&rhs.store; // Below prints 0 if previous writeln line is commented and -O is set. // Otherwise prints -9223372036854775808 as expected. writeln(compare(rhsPA, zis)); return compare(rhsPA, zis) == 0; } } static struct A { int a; } void main() { enforce(Foo(A(3)) != Foo(A(4))); } -- Configure issuemail: https://d.puremagic.com/issues/userprefs.cgi?tab=email ------- You are receiving this mail because: -------
Feb 14 2014
d-bugmail puremagic.com https://d.puremagic.com/issues/show_bug.cgi?id=12164 yebblies <yebblies gmail.com> changed: What |Removed |Added ---------------------------------------------------------------------------- CC| |yebblies gmail.com Wrong code, yummy! -- Configure issuemail: https://d.puremagic.com/issues/userprefs.cgi?tab=email ------- You are receiving this mail because: -------
Feb 15 2014
https://d.puremagic.com/issues/show_bug.cgi?id=12164 Kapps <opantm2+dbugs gmail.com> changed: What |Removed |Added ---------------------------------------------------------------------------- Severity|major |critical Raised priority to critical as it's a difficult to notice or track down (since trying to observe it with something like a writeln or setting a global variable causes it to no longer occur) bug that will silently result in different behaviour only in release mode. -- Configure issuemail: https://d.puremagic.com/issues/userprefs.cgi?tab=email ------- You are receiving this mail because: -------
Feb 16 2014
https://d.puremagic.com/issues/show_bug.cgi?id=12164 Reduced: ptrdiff_t compare(A* rhsPA, A* zis) { if (*rhsPA == *zis) return 0; return ptrdiff_t.min; } struct A { int a; } void main() { auto a = A(3); auto b = A(4); assert(!compare(&a, &b)); } The backend tried to emit OPmemcmp and screws it up somehow, probably missing a REX_W prefix or two. -- Configure issuemail: https://d.puremagic.com/issues/userprefs.cgi?tab=email ------- You are receiving this mail because: -------
Mar 06 2014
https://d.puremagic.com/issues/show_bug.cgi?id=12164 safety0ff.bugz <safety0ff.bugz gmail.com> changed: What |Removed |Added ---------------------------------------------------------------------------- CC| |safety0ff.bugz gmail.com 22:08:33 PDT ---The backend tried to emit OPmemcmp and screws it up somehow, probably missing a REX_W prefix or two.When I looked at the assembly on my end the memcmp looked fine. The emitted code for returning ptrdiff.min or 0 depending on the memcmp result looks like it has more than one issue in it. -- Configure issuemail: https://d.puremagic.com/issues/userprefs.cgi?tab=email ------- You are receiving this mail because: -------
Mar 09 2014
https://d.puremagic.com/issues/show_bug.cgi?id=12164 Commit pushed to master at https://github.com/D-Programming-Language/phobos https://github.com/D-Programming-Language/phobos/commit/6b91d4e1a1d385cf961ff6b68848bf3e0ca93245 Added workaround for bug 12164. Style: Fix lack of space after if. -- Configure issuemail: https://d.puremagic.com/issues/userprefs.cgi?tab=email ------- You are receiving this mail because: -------
Mar 15 2014
https://d.puremagic.com/issues/show_bug.cgi?id=12164If someone can identify exactly which instructions are wrong, and what they should be, I can probably fix it fairly easily. Otherwise it will have to wait, I don't have the energy to go digging through the assembly right now. -- Configure issuemail: https://d.puremagic.com/issues/userprefs.cgi?tab=email ------- You are receiving this mail because: -------The backend tried to emit OPmemcmp and screws it up somehow, probably missing a REX_W prefix or two.When I looked at the assembly on my end the memcmp looked fine. The emitted code for returning ptrdiff.min or 0 depending on the memcmp result looks like it has more than one issue in it.
Mar 15 2014
https://d.puremagic.com/issues/show_bug.cgi?id=12164 07:33:59 PDT ---If someone can identify exactly which instructions are wrong, and what they should be, I can probably fix it fairly easily. Otherwise it will have to wait, I don't have the energy to go digging through the assembly right now.I don't think the solution is as simple as you think (it's not a simple REX issue): Un-optimized (correct) assembly: 55 push RBP 48 8B EC mov RBP,RSP 48 83 EC 10 sub RSP,010h 48 B9 04 00 00 00 00 00 00 00 mov RCX,4 33 C0 xor EAX,EAX F3 rep A6 cmpsb 75 05 jne L1D 48 31 C0 xor RAX,RAX C9 leave C3 ret L1D: 48 B8 00 00 00 00 00 00 00 80 mov RAX,08000000000000000h C9 leave C3 ret Incorrect -O assembly: 55 push RBP 48 8B EC mov RBP,RSP 48 83 EC 10 sub RSP,010h 48 B9 04 00 00 00 00 00 00 00 mov RCX,4 33 C0 xor EAX,EAX F3 rep A6 cmpsb 74 05 je L1D 1B C0 sbb EAX,EAX 83 D8 FF sbb EAX,0FFFFFFFFFFFFFFFFh L1D: 83 F8 01 cmp EAX,1 19 C0 sbb EAX,EAX 31 C0 xor EAX,EAX 48 8B E5 mov RSP,RBP 5D pop RBP C3 ret As you can see, it invariantly returns zero after doing the memcmp. -- Configure issuemail: https://d.puremagic.com/issues/userprefs.cgi?tab=email ------- You are receiving this mail because: -------
Mar 31 2014
https://d.puremagic.com/issues/show_bug.cgi?id=12164 Orvid King <blah38621 gmail.com> changed: What |Removed |Added ---------------------------------------------------------------------------- CC| |blah38621 gmail.com One thing I am curious of in that generated code, why is it allocating 16 bytes on the stack when it doesn't use the stack? (sub RSP, 0x10) Also, I missing something here, but when did parameters start getting passed in ESI and EDI? As a bonus question, I have to ask, why are we doing that comparison with cmpsb when the size of the values being compared is known to be a multiple of 4, in which case, shouldn't we be using cmpsd? (this is quite literally a 4x speed improvement, as both instructions have the same cycle count) -- Configure issuemail: https://d.puremagic.com/issues/userprefs.cgi?tab=email ------- You are receiving this mail because: -------
Mar 31 2014
https://d.puremagic.com/issues/show_bug.cgi?id=12164One thing I am curious of in that generated code, why is it allocating 16 bytes on the stack when it doesn't use the stack? (sub RSP, 0x10) Also, I missing something here, but when did parameters start getting passed in ESI and EDI? As a bonus question, I have to ask, why are we doing that comparison with cmpsb when the size of the values being compared is known to be a multiple of 4, in which case, shouldn't we be using cmpsd? (this is quite literally a 4x speed improvement, as both instructions have the same cycle count)I seem to have forgotten about cmpsq, which is available on x64, for the same cycle count, which would be 8x faster. -- Configure issuemail: https://d.puremagic.com/issues/userprefs.cgi?tab=email ------- You are receiving this mail because: -------
Mar 31 2014