* Fwd: Help to understand instructions [not found] ` <CAJCbrz6n6V2OaXhJ+mRwsMZEwoyLGqV-znufOAKir78tcK_QWg@mail.gmail.com> @ 2012-11-07 12:49 ` Sergey Ivanov 2012-11-07 19:24 ` Kalle Olavi Niemitalo 0 siblings, 1 reply; 2+ messages in thread From: Sergey Ivanov @ 2012-11-07 12:49 UTC (permalink / raw) To: gcc-help Have compiled program with -g O3 together. Now learn it output via objdump (with code mixed format) and see (sorry for rather long one, just environment for question): .......... inline void Box::MinCoordDistance(double &r, const int i) const { if (r >= halfL[i]) 41f06d: f2 0f 10 48 38 movsd xmm1,QWORD PTR [rax+0x38] */ inline double Box::distanceSq(const Vec r1, const Vec r2, Vec dr) const { for (int i = 0; i < 3; i++) { dr[i] = r1[i] - r2[i]; 41f072: f2 41 0f 5c 40 10 subsd xmm0,QWORD PTR [r8+0x10] return distanceSq(r1, r2, dr); } inline void Box::MinCoordDistance(double &r, const int i) const { if (r >= halfL[i]) 41f078: 66 0f 2e c1 ucomisd xmm0,xmm1 */ inline double Box::distanceSq(const Vec r1, const Vec r2, Vec dr) const { for (int i = 0; i < 3; i++) { dr[i] = r1[i] - r2[i]; 41f07c: f2 0f 11 44 24 18 movsd QWORD PTR [rsp+0x18],xmm0 return distanceSq(r1, r2, dr); } inline void Box::MinCoordDistance(double &r, const int i) const { if (r >= halfL[i]) 41f082: 0f 83 50 01 00 00 jae 41f1d8 <CbDoubleBridgeBase<EnsembleNVT, Homopolymer>::scanBridgingForwardOne(int)+0x258> r -= L[i]; else if (r < -halfL[i]) 41f088: f2 0f 10 15 90 55 02 movsd xmm2,QWORD PTR [rip+0x25590] # 444620 <typeinfo name for SpeciesDependedMove<GeneralPolymerChain>+0x80> <<<<<<<<<<<<<<<question is here 41f08f: 00 41f090: 66 0f 57 ca xorpd xmm1,xmm2 41f094: 66 0f 2e c8 ucomisd xmm1,xmm0 41f098: 76 0b jbe 41f0a5 <CbDoubleBridgeBase<EnsembleNVT, Homopolymer>::scanBridgingForwardOne(int)+0x125> r += L[i]; 41f09a: f2 0f 58 40 20 addsd xmm0,QWORD PTR [rax+0x20] 41f09f: f2 0f 11 44 24 18 movsd QWORD PTR [rsp+0x18],xmm0 */ inline double Box::distanceSq(const Vec r1, const Vec r2, Vec dr) const { for (int i = 0; i < 3; i++) { dr[i] = r1[i] - r2[i]; 41f0a5: f2 0f 10 47 18 movsd xmm0,QWORD PTR [rdi+0x18] return distanceSq(r1, r2, dr); } inline void Box::MinCoordDistance(double &r, const int i) const { if (r >= halfL[i]) 41f0aa: f2 0f 10 48 40 movsd xmm1,QWORD PTR [rax+0x40] */ inline double Box::distanceSq(const Vec r1, const Vec r2, Vec dr) const { for (int i = 0; i < 3; i++) { dr[i] = r1[i] - r2[i]; 41f0af: f2 41 0f 5c 40 18 subsd xmm0,QWORD PTR [r8+0x18] return distanceSq(r1, r2, dr); } ................. What implicit addressation via rip means? Is it kind of protection or is it bug of objdump? -- Kind regards, Sergey Ivanov ^ permalink raw reply [flat|nested] 2+ messages in thread
* Re: Fwd: Help to understand instructions 2012-11-07 12:49 ` Fwd: Help to understand instructions Sergey Ivanov @ 2012-11-07 19:24 ` Kalle Olavi Niemitalo 0 siblings, 0 replies; 2+ messages in thread From: Kalle Olavi Niemitalo @ 2012-11-07 19:24 UTC (permalink / raw) To: Sergey Ivanov; +Cc: gcc-help Sergey Ivanov <icegood1980@gmail.com> writes: > else if (r < -halfL[i]) > 41f088: f2 0f 10 15 90 55 02 movsd xmm2,QWORD PTR > [rip+0x25590] # 444620 <typeinfo name for > SpeciesDependedMove<GeneralPolymerChain>+0x80> <<<<<<<<<<<<<<<question > is here [...] > What implicit addressation via rip means? Is it kind of protection or > is it bug of objdump? It just loads some constant from memory. I suppose the compiler did not emit a name for the constant in the debug information, so objdump displays the nearest preceding symbol, which happens to be typeinfo name for SpeciesDependedMove<GeneralPolymerChain>. Somewhat reproduced like this: #include <typeinfo> struct Box { double L[4]; double halfL[4]; void MinCoordDistance(double &r, const int i) const; }; const std::type_info &dummy = typeid(Box); void Box::MinCoordDistance(double &r, const int i) const { if (r >= halfL[i]) r -= L[i]; else if (r < -halfL[i]) r += L[i]; } Compiling this with g++ (Debian 4.7.1-7) 4.7.1, options -m64 -O3 -g -S: .file "xmm.c" .text .Ltext0: .align 2 .p2align 4,,15 .globl _ZNK3Box16MinCoordDistanceERdi .type _ZNK3Box16MinCoordDistanceERdi, @function _ZNK3Box16MinCoordDistanceERdi: .LFB19: .file 1 "xmm.c" .loc 1 13 0 .cfi_startproc .LVL0: .loc 1 14 0 movslq %edx, %rdx movsd (%rsi), %xmm0 movsd 32(%rdi,%rdx,8), %xmm1 ucomisd %xmm1, %xmm0 jae .L10 .loc 1 16 0 movsd .LC0(%rip), %xmm2 <<<<<<<<<<<<<<<question is here xorpd %xmm2, %xmm1 ucomisd %xmm0, %xmm1 jbe .L1 .loc 1 17 0 addsd (%rdi,%rdx,8), %xmm0 movsd %xmm0, (%rsi) .L1: rep ret .p2align 4,,10 .p2align 3 .L10: .loc 1 15 0 subsd (%rdi,%rdx,8), %xmm0 movsd %xmm0, (%rsi) ret .cfi_endproc .LFE19: .size _ZNK3Box16MinCoordDistanceERdi, .-_ZNK3Box16MinCoordDistanceERdi .globl dummy .section .rodata .align 8 .type dummy, @object .size dummy, 8 dummy: .quad _ZTI3Box .weak _ZTI3Box .section .rodata._ZTI3Box,"aG",@progbits,_ZTI3Box,comdat .align 16 .type _ZTI3Box, @object .size _ZTI3Box, 16 _ZTI3Box: .quad _ZTVN10__cxxabiv117__class_type_infoE+16 .quad _ZTS3Box .weak _ZTS3Box .section .rodata._ZTS3Box,"aG",@progbits,_ZTS3Box,comdat .type _ZTS3Box, @object .size _ZTS3Box, 5 _ZTS3Box: .string "3Box" .section .rodata.cst16,"aM",@progbits,16 .align 16 .LC0: .long 0 .long -2147483648 .long 0 .long 0 .text ... the rest omitted for brevity. The "movsd .LC0(%rip), %xmm2" instruction loads a value from .LC0, which is in the rodata.cst16 section and is thus a constant. It looks like this constant is double[2] { -0.0, 0.0 } and the function computes -halfL[i] by toggling the sign bit with xor. The debug information in the assembly file does not refer to .LC0. ^ permalink raw reply [flat|nested] 2+ messages in thread
end of thread, other threads:[~2012-11-07 19:24 UTC | newest]
Thread overview: 2+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
[not found] <CAJCbrz5L5YabB5BEeS4gi-ybbZxNqggKqTknTaeU6SswM5hz0Q@mail.gmail.com>
[not found] ` <CAJCbrz6n6V2OaXhJ+mRwsMZEwoyLGqV-znufOAKir78tcK_QWg@mail.gmail.com>
2012-11-07 12:49 ` Fwd: Help to understand instructions Sergey Ivanov
2012-11-07 19:24 ` Kalle Olavi Niemitalo
This is a public inbox, see mirroring instructions for how to clone and mirror all data and code used for this inbox; as well as URLs for read-only IMAP folder(s) and NNTP newsgroup(s).