https://gcc.gnu.org/bugzilla/show_bug.cgi?id=27077
--- Comment #8 from Helmut Schellong <var at schellong dot biz> ---
Test case is a special measurement program.
See assembler code below:
strlen / repnz scasb
clock_gettime
gcc6 + gcc5
The exact gcc version is not critical.
Each gcc that injects an intel string instruction
injects slow code (on many cpus).
Practical experience (use) is important.
CPU: Intel(R) Core(TM)2 Duo CPU E8600 @ 3.33GHz (3333.40-MHz K8-class CPU)
Origin = "GenuineIntel" Id = 0x1067a Family = 0x6 Model = 0x17 Stepping =
10
Features=0xbfebfbff<FPU,VME,DE,PSE,TSC,MSR,PAE,MCE,CX8,APIC,SEP,MTRR,PGE,MCA,CMOV,PAT,PSE36,CLFLUSH,DTS,ACPI,MMX,FXSR,SSE,SSE2,SS,HTT,TM,PBE>
Features2=0xc08e3fd<SSE3,DTES64,MON,DS_CPL,VMX,SMX,EST,TM2,SSSE3,CX16,xTPR,PDCM,SSE4.1,XSAVE,OSXSAVE>
AMD Features=0x20100800<SYSCALL,NX,LM>
AMD Features2=0x1<LAHF>
VT-x: HLT,PAUSE
TSC: P-state invariant, performance statistics
gcc6 -v
Using built-in specs.
COLLECT_GCC=gcc6
COLLECT_LTO_WRAPPER=/usr/local/libexec/gcc6/gcc/x86_64-portbld-freebsd10.1/6.2.0/lto-wrapper
Target: x86_64-portbld-freebsd10.1
Configured with: ...
Thread model: posix
gcc version 6.2.0 (FreeBSD Ports Collection)
gcc5 -v
Using built-in specs.
COLLECT_GCC=gcc5
COLLECT_LTO_WRAPPER=/usr/local/libexec/gcc5/gcc/x86_64-portbld-freebsd10.0/5.0.0/lto-wrapper
Target: x86_64-portbld-freebsd10.0
Configured with: ...
Thread model: posix
gcc version 5.0.0 20140921 (experimental) (FreeBSD Ports Collection)
gcc6 -O1 -static -s -opt -fno-builtin-strlen -DSTRLENF pt.c ptf.o
==============================================================================
lea rsi, [rsp+32] #,
mov edi, 1 #,
call clock_gettime #
mov ebx, DWORD PTR CntA[rip] # is, CntA
.p2align 2
.L10:
mov edi, OFFSET FLAT:DA #,
call strlen #
mov QWORD PTR [rsp+112], rax # L, _80
sub ebx, 1 # is,
test ebx, ebx # is
jg .L10 #,
lea rsi, [rsp+64] # tmp273,
mov edi, 1 #,
call clock_gettime #
imul rax, QWORD PTR [rsp+64], 1000000000 # tmp216, cb[0].tv_sec,
add rax, QWORD PTR [rsp+72] # tmp218, cb[0].tv_nsec
imul rdx, QWORD PTR [rsp+32], 1000000000 # tmp220, ca[0].tv_sec,
add rdx, QWORD PTR [rsp+40] # tmp222, ca[0].tv_nsec
sub rax, rdx # tmp224, tmp222
pxor xmm7, xmm7 # _94
cvtsi2sdq xmm7, rax # _94, tmp224
movsd QWORD PTR [rsp+8], xmm7 # %sfp, _94
mov rsi, QWORD PTR [rsp+112] # L.7_105, L
mov edi, OFFSET FLAT:.LC3 #,
mov eax, 0 #,
call printf #
lea rsi, [rsp+32] #,
mov edi, 1 #,
call clock_gettime #
mov ebx, DWORD PTR CntA[rip] # is, CntA
.p2align 2
.L11:
mov edi, OFFSET FLAT:DA #,
call strlen #
mov QWORD PTR [rsp+112], rax # L, _112
mov edi, OFFSET FLAT:DA #,
call strlen #
mov QWORD PTR [rsp+112], rax # L, _115
sub ebx, 1 # is,
test ebx, ebx # is
jg .L11 #,
lea rsi, [rsp+64] # tmp275,
mov edi, 1 #,
call clock_gettime #
==============================================================================
gcc6 -O1 -static -s -opt -DSTRLENF pt.c ptf.o
==============================================================================
lea rsi, [rsp+32] #,
mov edi, 1 #,
call clock_gettime #
mov edx, DWORD PTR CntA[rip] # is, CntA
mov rsi, -1 # tmp225,
mov eax, 0 # tmp226,
.p2align 2
.L10:
mov edi, OFFSET FLAT:DA # tmp224,
mov rcx, rsi # tmp222, tmp225
repnz scasb
not rcx # tmp223
sub rcx, 1 # _80,
mov QWORD PTR [rsp+112], rcx # L, _80
sub edx, 1 # is,
test edx, edx # is
jg .L10 #,
lea rsi, [rsp+64] # tmp299,
mov edi, 1 #,
call clock_gettime #
imul rax, QWORD PTR [rsp+64], 1000000000 # tmp228, cb[0].tv_sec,
add rax, QWORD PTR [rsp+72] # tmp230, cb[0].tv_nsec
imul rdx, QWORD PTR [rsp+32], 1000000000 # tmp232, ca[0].tv_sec,
add rdx, QWORD PTR [rsp+40] # tmp234, ca[0].tv_nsec
sub rax, rdx # tmp236, tmp234
pxor xmm7, xmm7 # _94
cvtsi2sdq xmm7, rax # _94, tmp236
movsd QWORD PTR [rsp+8], xmm7 # %sfp, _94
mov rsi, QWORD PTR [rsp+112] # L.7_105, L
mov edi, OFFSET FLAT:.LC3 #,
mov eax, 0 #,
call printf #
lea rsi, [rsp+32] #,
mov edi, 1 #,
call clock_gettime #
mov edx, DWORD PTR CntA[rip] # is, CntA
mov rsi, -1 # tmp242,
mov eax, 0 # tmp243,
.p2align 2
.L11:
mov edi, OFFSET FLAT:DA # tmp241,
mov rcx, rsi # tmp239, tmp242
repnz scasb
not rcx # tmp240
sub rcx, 1 # _112,
mov QWORD PTR [rsp+112], rcx # L, _112
mov edi, OFFSET FLAT:DA # tmp247,
mov rcx, rsi # tmp245, tmp242
repnz scasb
not rcx # tmp246
sub rcx, 1 # _115,
mov QWORD PTR [rsp+112], rcx # L, _115
sub edx, 1 # is,
test edx, edx # is
jg .L11 #,
lea rsi, [rsp+64] # tmp303,
mov edi, 1 #,
call clock_gettime #
==============================================================================
gcc5 -O1 -static -s -opt -DSTRLENF pt.c ptf.o
==============================================================================
lea rsi, [rsp+32] #,
mov edi, 1 #,
call clock_gettime #
mov esi, DWORD PTR CntA[rip] # is, CntA
mov r8, -1 # tmp286,
mov eax, 0 # tmp287,
.p2align 2
.L10:
mov edi, OFFSET FLAT:DA # tmp221,
mov rcx, r8 # tmp219, tmp286
repnz scasb
not rcx # tmp220
mov rdx, rcx # tmp220, tmp220
sub rdx, 1 # D.3715,
mov QWORD PTR [rsp+112], rdx # L, D.3715
sub esi, 1 # is,
test esi, esi # is
jg .L10 #,
lea rsi, [rsp+64] # tmp296,
mov edi, 1 #,
call clock_gettime #
imul rax, QWORD PTR [rsp+64], 1000000000 # D.3716, cb[0].tv_sec,
add rax, QWORD PTR [rsp+72] # D.3716, cb[0].tv_nsec
mov rdx, rax # D.3716, D.3716
imul rax, QWORD PTR [rsp+32], -1000000000 # D.3716, ca[0].tv_sec,
sub rax, QWORD PTR [rsp+40] # D.3716, ca[0].tv_nsec
add rax, rdx # D.3716, D.3716
pxor xmm7, xmm7 # D.3718
cvtsi2sdq xmm7, rax # D.3718, D.3716
movsd QWORD PTR [rsp+8], xmm7 # %sfp, D.3718
mov rsi, QWORD PTR [rsp+112] # D.3716, L
mov edi, OFFSET FLAT:.LC3 #,
mov eax, 0 #,
call printf #
lea rsi, [rsp+32] #,
mov edi, 1 #,
call clock_gettime #
mov esi, DWORD PTR CntA[rip] # is, CntA
mov r8, -1 # tmp284,
mov eax, 0 # tmp285,
.p2align 2
.L11:
mov edi, OFFSET FLAT:DA # tmp237,
mov rcx, r8 # tmp235, tmp284
repnz scasb
not rcx # tmp236
mov rdx, rcx # tmp236, tmp236
sub rdx, 1 # D.3715,
mov QWORD PTR [rsp+112], rdx # L, D.3715
mov edi, OFFSET FLAT:DA # tmp243,
mov rcx, r8 # tmp241, tmp284
repnz scasb
not rcx # tmp242
mov rdx, rcx # tmp242, tmp242
sub rdx, 1 # D.3715,
mov QWORD PTR [rsp+112], rdx # L, D.3715
sub esi, 1 # is,
test esi, esi # is
jg .L11 #,
lea rsi, [rsp+64] # tmp303,
mov edi, 1 #,
call clock_gettime #
==============================================================================
