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- Pragma directive [ #pragma optimize ( "", off | on ) ] - Does it really work?
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SKost
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09-23-2016
08:51 PM
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Pragma directive [ #pragma optimize ( "", off | on ) ] - Does it really work?
*** Pragma directive [ #pragma optimize ( "", off | on ) ] - Does it really work? ***
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SKost
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09-23-2016
08:57 PM
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[ Abstract ]
Pragma directive [ #pragma optimize ( "", off | on ) ] - Does it really work?
A set of tests was completed for Microsoft and Intel C++ compilers and it looks
like the directive does not work. Generated binary codes are the same when the switch is on or off.
SKost
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09-23-2016
09:00 PM
133 Views
[ Microsoft C++ compiler ]
...
#pragma optimize ( "", on )
// C/C++ codes for a function
...
Assembler codes
...
00248B10 push ebp
00248B11 mov ebp, esp
00248B13 sub esp, 10h
00248B16 push esi
00248B17 rdtsc
00248B19 mov dword ptr [ebp-10h], eax
00248B1C mov dword ptr [ebp-0Ch], edx
00248B1F mov eax, dword ptr [ebp+8]
00248B22 clflush [eax]
00248B25 rdtsc
00248B27 mov dword ptr [ebp-8], eax
00248B2A mov dword ptr [ebp-4], edx
00248B2D mov edx, dword ptr [ebp-8]
00248B30 mov eax, dword ptr [ebp-4]
00248B33 mov ecx, dword ptr [ebp-10h]
00248B36 mov esi, dword ptr [ebp-0Ch]
00248B39 sub edx, ecx
00248B3B sbb eax, esi
00248B3D push edx
00248B3E push 24C420h
00248B43 call dword ptr ds:[24A234h]
00248B49 add esp, 8
00248B4C pop esi
00248B4D mov esp, ebp
00248B4F pop ebp
00248B50 ret
...
SKost
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09-23-2016
09:04 PM
133 Views
[ Microsoft C++ compiler ]
...
#pragma optimize ( "", off )
// C/C++ codes for a function
...
Assembler codes
...
00248B10 push ebp
00248B11 mov ebp, esp
00248B13 sub esp, 10h
00248B16 push esi
00248B17 rdtsc
00248B19 mov dword ptr [ebp-10h], eax
00248B1C mov dword ptr [ebp-0Ch], edx
00248B1F mov eax, dword ptr [ebp+8]
00248B22 clflush [eax]
00248B25 rdtsc
00248B27 mov dword ptr [ebp-8], eax
00248B2A mov dword ptr [ebp-4], edx
00248B2D mov edx, dword ptr [ebp-8]
00248B30 mov eax, dword ptr [ebp-4]
00248B33 mov ecx, dword ptr [ebp-10h]
00248B36 mov esi, dword ptr [ebp-0Ch]
00248B39 sub edx, ecx
00248B3B sbb eax, esi
00248B3D push edx
00248B3E push 24C420h
00248B43 call dword ptr ds:[24A234h]
00248B49 add esp, 8
00248B4C pop esi
00248B4D mov esp, ebp
00248B4F pop ebp
00248B50 ret
...
SKost
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09-23-2016
09:08 PM
133 Views
[ Intel C++ compiler ]
...
#pragma optimize ( "", on )
// C/C++ codes for a function
...
Assembler codes
...
004034A0 push ebp
004034A1 mov ebp, esp
004034A3 sub esp, 38h
004034A6 rdtsc
004034A8 mov dword ptr [ebp-30h], eax
004034AB mov dword ptr [ebp-2Ch], edx
004034AE mov eax, dword ptr [ebp-30h]
004034B1 mov edx, dword ptr [ebp-2Ch]
004034B4 mov dword ptr [ebp-28h], eax
004034B7 mov dword ptr [ebp-24h], edx
004034BA mov eax, dword ptr [ebp+8]
004034BD clflush [eax]
004034C0 rdtsc
004034C2 mov dword ptr [ebp-20h], eax
004034C5 mov dword ptr [ebp-1Ch], edx
004034C8 mov eax, dword ptr [ebp-20h]
004034CB mov edx, dword ptr [ebp-1Ch]
004034CE mov dword ptr [ebp-18h], eax
004034D1 mov dword ptr [ebp-14h], edx
004034D4 mov eax, dword ptr [ebp-18h]
004034D7 mov edx, dword ptr [ebp-14h]
004034DA mov dword ptr [ebp-10h], eax
004034DD mov dword ptr [ebp-0Ch], edx
004034E0 mov eax, dword ptr [ebp-28h]
004034E3 mov edx, dword ptr [ebp-24h]
004034E6 mov dword ptr [ebp-8], eax
004034E9 mov dword ptr [ebp-4], edx
004034EC add esp, 0FFFFFFF8h
004034EF mov dword ptr [esp], 425F60h
004034F6 mov eax, dword ptr [ebp-8]
004034F9 mov edx, 0
004034FE sub edx, eax
00403500 add edx, dword ptr [ebp-10h]
00403503 mov dword ptr [esp+4], edx
00403507 call InitMemoryTracer+12Dh (40A821h)
0040350C add esp, 8
0040350F mov dword ptr [ebp-38h], eax
00403512 leave
00403513 ret
...
SKost
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09-23-2016
09:11 PM
133 Views
[ Intel C++ compiler ]
...
#pragma optimize ( "", off )
// C/C++ codes for a function
...
Assembler codes
...
004034A0 push ebp
004034A1 mov ebp, esp
004034A3 sub esp, 38h
004034A6 rdtsc
004034A8 mov dword ptr [ebp-30h], eax
004034AB mov dword ptr [ebp-2Ch], edx
004034AE mov eax, dword ptr [ebp-30h]
004034B1 mov edx, dword ptr [ebp-2Ch]
004034B4 mov dword ptr [ebp-28h], eax
004034B7 mov dword ptr [ebp-24h], edx
004034BA mov eax, dword ptr [ebp+8]
004034BD clflush [eax]
004034C0 rdtsc
004034C2 mov dword ptr [ebp-20h], eax
004034C5 mov dword ptr [ebp-1Ch], edx
004034C8 mov eax, dword ptr [ebp-20h]
004034CB mov edx, dword ptr [ebp-1Ch]
004034CE mov dword ptr [ebp-18h], eax
004034D1 mov dword ptr [ebp-14h], edx
004034D4 mov eax, dword ptr [ebp-18h]
004034D7 mov edx, dword ptr [ebp-14h]
004034DA mov dword ptr [ebp-10h], eax
004034DD mov dword ptr [ebp-0Ch], edx
004034E0 mov eax, dword ptr [ebp-28h]
004034E3 mov edx, dword ptr [ebp-24h]
004034E6 mov dword ptr [ebp-8], eax
004034E9 mov dword ptr [ebp-4], edx
004034EC add esp, 0FFFFFFF8h
004034EF mov dword ptr [esp], 425F60h
004034F6 mov eax, dword ptr [ebp-8]
004034F9 mov edx, 0
004034FE sub edx, eax
00403500 add edx, dword ptr [ebp-10h]
00403503 mov dword ptr [esp+4], edx
00403507 call InitMemoryTracer+12Dh (40A821h)
0040350C add esp, 8
0040350F mov dword ptr [ebp-38h], eax
00403512 leave
00403513 ret
...
SKost
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09-25-2016
10:48 AM
133 Views
[ Command Line Options ]
[ Microsoft C++ compiler ( VS2005 PE ) 32-bit ]
[ Compiler ]
/O2 /Ob1 /Oi /Ot /Oy /GL /I "..\..\Include" /D "WIN32" /D "_CONSOLE" /D "NDEBUG" /D "_WIN32_MSC" /D "_VC80_UPGRADE=0x0710" /D "_UNICODE" /D "UNICODE" /GF /Gm /MT /GS- /fp:fast /GR- /openmp /Yu"Stdphf.h" /Fp"Release\MscTestApp.pch" /Fo"Release/" /Fd"Release/" /W4 /nologo /c /Wp64 /Zi /Gd /TP /wd4005 /U "_WINCE_MSC" /U "WIN32_PLATFORM_PSPC" /U "WIN32_PLATFORM_WFSP" /U "WIN32_PLATFORM_WM50" /U "_WIN32_MGW" /U "_WIN32_BCC" /U "_COS16_TCC" /U "_WIN32_ICC" /U "_WIN32_WCC" /errorReport:prompt /arch:SSE2
[ Linker ]
/OUT:"Release/MscTestApp.exe" /INCREMENTAL:NO /NOLOGO /MANIFEST /MANIFESTFILE:"Release\MscTestApp.exe.intermediate.manifest" /NODEFAULTLIB:"../../Bin/Release/ScaLib.lib" /SUBSYSTEM:CONSOLE /STACK:268435456 /LARGEADDRESSAWARE /LTCG /MACHINE:X86 /ERRORREPORT:PROMPT kernel32.lib user32.lib gdi32.lib winspool.lib comdlg32.lib advapi32.lib shell32.lib ole32.lib oleaut32.lib uuid.lib odbc32.lib odbccp32.lib "..\..\bin\release\scalib.lib"
SKost
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09-25-2016
11:18 AM
133 Views
[ Command Line Options ]
[ Intel C++ compiler v12.1.7 ( u371 ) 32-bit ]
[ Compiler ]
/c /O3 /Ob1 /Oi /Ot /Oy /Qipo /I "..\..\Include" /D "WIN32" /D "_CONSOLE" /D "NDEBUG" /D "_WIN32_ICC" /D "INTEL_SUITE_VERSION=PE121_300" /D "_VC80_UPGRADE=0x0710" /D "_UNICODE" /D "UNICODE" /GF /MT /GS- /fp:fast=2 /GR- /Yu"Stdphf.h" /Fp"Release\IccTestApp.pch" /Fo"Release/" /W5 /nologo /Wp64 /Zi /Gd /TP /Qdiag-disable:2012 /Qdiag-disable:2013 /Qdiag-disable:2014 /Qdiag-disable:2015 /Qdiag-disable:2017 /Qdiag-disable:2021 /Qdiag-disable:2022 /Qdiag-disable:2304 /U "_WIN32_MSC" /U "_WINCE_MSC" /U "WIN32_PLATFORM_PSPC" /U "WIN32_PLATFORM_WFSP" /U "WIN32_PLATFORM_WM50" /U "_WIN32_MGW" /U "_WIN32_BCC" /U "_COS16_TCC" /U "_WIN32_WCC" /Qopenmp /Qfp-speculation:fast /Qopt-matmul /Qparallel /Qstd=c++0x /Qrestrict /Qdiag-disable:111,673,10121
/Wport /Qeffc++ /QxSSE2 /Qansi-alias /Qvec-report=0 /Qfma /Qunroll:8 /Qunroll-aggressive /Qopt-streaming-stores:always /Qopt-block-factor:128 /Qopt-mem-layout-trans:2 /Wport /Qeffc++ /QxSSE2 /Qansi-alias /Qvec-report=0 /Qfma /Qunroll:8 /Qunroll-aggressive /Qopt-streaming-stores:always /Qopt-block-factor:128 /Qopt-mem-layout-trans:2
[ Linker ]
kernel32.lib user32.lib gdi32.lib winspool.lib comdlg32.lib advapi32.lib shell32.lib ole32.lib oleaut32.lib uuid.lib odbc32.lib odbccp32.lib /OUT:"Release/IccTestApp.exe" /INCREMENTAL:NO /nologo /MANIFEST /MANIFESTFILE:"Release\IccTestApp.exe.intermediate.manifest" /NODEFAULTLIB:"../../Bin/Release/ScaLib.lib" /TLBID:1 /SUBSYSTEM:CONSOLE /STACK:268435456 /LARGEADDRESSAWARE /MACHINE:X86 /qdiag-disable:111,673,10121
SKost
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09-25-2016
11:25 AM
133 Views
[ C codes for the function]
...
// #pragma optimize ( "", on )
// #pragma optimize ( "", off )
_RTINLINE RTvoid CrtClflush( RTvoid RTconst *pvAddress )
{
_RTvolatile RTuint64 uiClock1 = IrtRdtsc();
IrtClflush( pvAddress );
_RTvolatile RTuint64 uiClock2 = IrtRdtsc();
CrtPrintf( RTU("[ CrtClflush ] - Executed in %u clock cycles\n"),
( RTuint )( uiClock2 - uiClock1 ) );
}
...
For more complete information about compiler optimizations, see our Optimization Notice.