我一直在阅读有关因Intel CPU的地址位6至11含糊不清而导致的加载/存储重叠导致的4K别名。因此，我试图编写各种简单的测试（在i7-3770k，Win7、64位，VS2017上）专门引起该问题，以确保我在实践中理解它。
我一直在尝试但未能证明其行为的第一个测试是：
void Test4KAliasing1()
{
typedef float Value;// Also tried with double
const uint32_t ValueCount = 1024;
const uint32_t OffsetCount = 256;
const uint32_t TestCount = 512;
Value* a = (Value*)_aligned_malloc(ValueCount * sizeof(Value), 4096);
Value* b = (Value*)_aligned_malloc(ValueCount * sizeof(Value), 4096);
for (uint32_t i = 0; i < ValueCount; ++i)
a[i] = b[i] = (Value)rand();
for (uint32_t offset = 0; offset < OffsetCount; ++offset)
{
uint64_t startTime = StartCPUCycles();
for (uint32_t test = 0; test < TestCount; ++test)
{
for (uint32_t i = 0; i < ValueCount; ++i)
{
uint32_t j = (offset + i) % ValueCount;
a[i] += b[j] * 3.142f;
}
}
uint64_t duration = EndCPUCycles() - startTime;
printf("time: %llu\toffset: %u ", duration / TestCount, offset);
printf("\n", a, b);
}
_aligned_free(b);
_aligned_free(a);
}
灵感来自于http://richardstartin.uk/the-much-aligned-garbage-collector/
所以我不太确定为什么从最终的计时结果来看并没有显示出问题？就像我认为的那样，由于乱序执行，存储会在循环迭代中加载到不明确的地址或从不明确的地址进行加载？
生成的程序集为：
000000013F2510E4 cpuid
000000013F2510E6 rdtsc
000000013F2510E8 shl rdx,20h
000000013F2510EC mov r9d,200h
000000013F2510F2 or rax,rdx
000000013F2510F5 mov r10,rax
000000013F2510F8 nop dword ptr [rax+rax]
000000013F251100 lea ebx,[rsi+1]
000000013F251103 mov r8d,80h
000000013F251109 lea rdx,[r14+8]
000000013F25110D nop dword ptr [rax]
000000013F251110 mov rax,rbx
000000013F251113 lea ecx,[rbx-1]
000000013F251116 and eax,3FFh
000000013F25111B lea rdx,[rdx+20h]
000000013F25111F and ecx,3FFh
000000013F251125 vmulss xmm1,xmm6,dword ptr [rdi+rcx*4]
000000013F25112A vaddss xmm2,xmm1,dword ptr [rdx-28h]
000000013F25112F vmovss dword ptr [rdx-28h],xmm2
000000013F251134 vmulss xmm1,xmm6,dword ptr [rdi+rax*4]
000000013F251139 vaddss xmm2,xmm1,dword ptr [rdx-24h]
000000013F25113E vmovss dword ptr [rdx-24h],xmm2
000000013F251143 lea eax,[rbx+1]
000000013F251146 and eax,3FFh
000000013F25114B vmulss xmm1,xmm6,dword ptr [rdi+rax*4]
000000013F251150 vaddss xmm2,xmm1,dword ptr [rdx-20h]
000000013F251155 vmovss dword ptr [rdx-20h],xmm2
000000013F25115A lea eax,[rbx+2]
000000013F25115D and eax,3FFh
000000013F251162 vmulss xmm1,xmm6,dword ptr [rdi+rax*4]
000000013F251167 vaddss xmm2,xmm1,dword ptr [rdx-1Ch]
000000013F25116C vmovss dword ptr [rdx-1Ch],xmm2
000000013F251171 lea eax,[rbx+3]
000000013F251174 and eax,3FFh
000000013F251179 vmulss xmm1,xmm6,dword ptr [rdi+rax*4]
000000013F25117E vaddss xmm2,xmm1,dword ptr [rdx-18h]
000000013F251183 vmovss dword ptr [rdx-18h],xmm2
000000013F251188 lea eax,[rbx+4]
000000013F25118B and eax,3FFh
000000013F251190 vmulss xmm1,xmm6,dword ptr [rdi+rax*4]
000000013F251195 vaddss xmm2,xmm1,dword ptr [rdx-14h]
000000013F25119A vmovss dword ptr [rdx-14h],xmm2
000000013F25119F lea eax,[rbx+5]
000000013F2511A2 and eax,3FFh
000000013F2511A7 vmulss xmm1,xmm6,dword ptr [rdi+rax*4]
000000013F2511AC vaddss xmm2,xmm1,dword ptr [rdx-10h]
000000013F2511B1 lea eax,[rbx+6]
000000013F2511B4 add ebx,8
000000013F2511B7 vmovss dword ptr [rdx-10h],xmm2
000000013F2511BC and eax,3FFh
000000013F2511C1 vmulss xmm1,xmm6,dword ptr [rdi+rax*4]
000000013F2511C6 vaddss xmm2,xmm1,dword ptr [rdx-0Ch]
000000013F2511CB vmovss dword ptr [rdx-0Ch],xmm2
000000013F2511D0 sub r8,1
000000013F2511D4 jne Test4KAliasing1+0B0h (013F251110h)
000000013F2511DA sub r9,1
000000013F2511DE jne Test4KAliasing1+0A0h (013F251100h)
000000013F2511E4 rdtsc
我还在网上看到各种描述，说最低的12位必须匹配才能发生这种混叠，而在其他地方，只有6到11位？由于最低的6位是高速缓存行中的字节索引，而且所有内容都是基于高速缓存行的，所以我想它只需要6至11位就可以匹配？
编辑：
也根据彼得斯的回答，我尝试过：
a[i] *= 1.234f;
b[j] += 4.321f;
似乎没有显示出问题并生成：
000000013F6C10E8 cpuid
000000013F6C10EA rdtsc
000000013F6C10EC shl rdx,20h
000000013F6C10F0 mov ebx,200h
000000013F6C10F5 or rax,rdx
000000013F6C10F8 mov r9,rax
000000013F6C10FB nop dword ptr [rax+rax]
000000013F6C1100 lea edx,[rsi+1]
000000013F6C1103 mov r8d,80h
000000013F6C1109 lea rcx,[r14+8]
000000013F6C110D nop dword ptr [rax]
000000013F6C1110 vmulss xmm1,xmm6,dword ptr [rcx-8]
000000013F6C1115 vmovss dword ptr [rcx-8],xmm1
000000013F6C111A lea eax,[rdx-1]
000000013F6C111D and eax,3FFh
000000013F6C1122 lea rcx,[rcx+20h]
000000013F6C1126 vaddss xmm1,xmm7,dword ptr [rdi+rax*4]
000000013F6C112B vmovss dword ptr [rdi+rax*4],xmm1
000000013F6C1130 vmulss xmm1,xmm6,dword ptr [rcx-24h]
000000013F6C1135 vmovss dword ptr [rcx-24h],xmm1
000000013F6C113A mov rax,rdx
000000013F6C113D and eax,3FFh
000000013F6C1142 vaddss xmm1,xmm7,dword ptr [rdi+rax*4]
000000013F6C1147 vmovss dword ptr [rdi+rax*4],xmm1
000000013F6C114C vmulss xmm0,xmm6,dword ptr [rcx-20h]
000000013F6C1151 lea eax,[rdx+1]
000000013F6C1154 and eax,3FFh
000000013F6C1159 vmovss dword ptr [rcx-20h],xmm0
000000013F6C115E vaddss xmm1,xmm7,dword ptr [rdi+rax*4]
000000013F6C1163 vmovss dword ptr [rdi+rax*4],xmm1
000000013F6C1168 vmulss xmm1,xmm6,dword ptr [rcx-1Ch]
000000013F6C116D vmovss dword ptr [rcx-1Ch],xmm1
000000013F6C1172 lea eax,[rdx+2]
000000013F6C1175 and eax,3FFh
000000013F6C117A vaddss xmm1,xmm7,dword ptr [rdi+rax*4]
000000013F6C117F vmovss dword ptr [rdi+rax*4],xmm1
000000013F6C1184 vmulss xmm1,xmm6,dword ptr [rcx-18h]
000000013F6C1189 vmovss dword ptr [rcx-18h],xmm1
000000013F6C118E lea eax,[rdx+3]
000000013F6C1191 and eax,3FFh
000000013F6C1196 vaddss xmm1,xmm7,dword ptr [rdi+rax*4]
000000013F6C119B vmovss dword ptr [rdi+rax*4],xmm1
000000013F6C11A0 vmulss xmm1,xmm6,dword ptr [rcx-14h]
000000013F6C11A5 vmovss dword ptr [rcx-14h],xmm1
000000013F6C11AA lea eax,[rdx+4]
000000013F6C11AD and eax,3FFh
000000013F6C11B2 vaddss xmm1,xmm7,dword ptr [rdi+rax*4]
000000013F6C11B7 vmovss dword ptr [rdi+rax*4],xmm1
000000013F6C11BC vmulss xmm1,xmm6,dword ptr [rcx-10h]
000000013F6C11C1 lea eax,[rdx+5]
000000013F6C11C4 and eax,3FFh
000000013F6C11C9 vmovss dword ptr [rcx-10h],xmm1
000000013F6C11CE vaddss xmm1,xmm7,dword ptr [rdi+rax*4]
000000013F6C11D3 vmovss dword ptr [rdi+rax*4],xmm1
000000013F6C11D8 vmulss xmm1,xmm6,dword ptr [rcx-0Ch]
000000013F6C11DD lea eax,[rdx+6]
000000013F6C11E0 add edx,8
000000013F6C11E3 and eax,3FFh
000000013F6C11E8 vmovss dword ptr [rcx-0Ch],xmm1
000000013F6C11ED vaddss xmm1,xmm7,dword ptr [rdi+rax*4]
000000013F6C11F2 vmovss dword ptr [rdi+rax*4],xmm1
000000013F6C11F7 sub r8,1
000000013F6C11FB jne Test4KAliasing1+0B0h (013F6C1110h)
000000013F6C1201 sub rbx,1
000000013F6C1205 jne Test4KAliasing1+0A0h (013F6C1100h)
000000013F6C120B rdtsc
还基于彼得提到的链接问题，我尝试了3个数组：
a[i] += b[j] + c[j];
似乎也没有问题。生成的代码是：
000000013F5110F6 cpuid
000000013F5110F8 rdtsc
000000013F5110FA shl rdx,20h
000000013F5110FE mov r8d,200h
000000013F511104 or rax,rdx
000000013F511107 mov r10,rax
000000013F51110A nop word ptr [rax+rax]
000000013F511110 lea ebx,[rbp+1]
000000013F511113 mov r9d,100h
000000013F511119 lea rdx,[r13+8]
000000013F51111D nop dword ptr [rax]
000000013F511120 mov rax,rbx
000000013F511123 lea ecx,[rbx-1]
000000013F511126 and eax,7FFh
000000013F51112B lea rdx,[rdx+20h]
000000013F51112F and ecx,7FFh
000000013F511135 vmovss xmm0,dword ptr [rsi+rcx*4]
000000013F51113A vaddss xmm1,xmm0,dword ptr [rdi+rcx*4]
000000013F51113F vaddss xmm2,xmm1,dword ptr [rdx-28h]
000000013F511144 vmovss dword ptr [rdx-28h],xmm2
000000013F511149 vmovss xmm0,dword ptr [rsi+rax*4]
000000013F51114E vaddss xmm1,xmm0,dword ptr [rdi+rax*4]
000000013F511153 vaddss xmm2,xmm1,dword ptr [rdx-24h]
000000013F511158 vmovss dword ptr [rdx-24h],xmm2
000000013F51115D lea eax,[rbx+1]
000000013F511160 and eax,7FFh
000000013F511165 vmovss xmm0,dword ptr [rsi+rax*4]
000000013F51116A vaddss xmm1,xmm0,dword ptr [rdi+rax*4]
000000013F51116F vaddss xmm2,xmm1,dword ptr [rdx-20h]
000000013F511174 vmovss dword ptr [rdx-20h],xmm2
000000013F511179 lea eax,[rbx+2]
000000013F51117C and eax,7FFh
000000013F511181 vmovss xmm0,dword ptr [rsi+rax*4]
000000013F511186 vaddss xmm1,xmm0,dword ptr [rdi+rax*4]
000000013F51118B vaddss xmm2,xmm1,dword ptr [rdx-1Ch]
000000013F511190 vmovss dword ptr [rdx-1Ch],xmm2
000000013F511195 lea eax,[rbx+3]
000000013F511198 and eax,7FFh
000000013F51119D vmovss xmm0,dword ptr [rsi+rax*4]
000000013F5111A2 vaddss xmm1,xmm0,dword ptr [rdi+rax*4]
000000013F5111A7 vaddss xmm2,xmm1,dword ptr [rdx-18h]
000000013F5111AC vmovss dword ptr [rdx-18h],xmm2
000000013F5111B1 lea eax,[rbx+4]
000000013F5111B4 and eax,7FFh
000000013F5111B9 vmovss xmm0,dword ptr [rsi+rax*4]
000000013F5111BE vaddss xmm1,xmm0,dword ptr [rdi+rax*4]
000000013F5111C3 vaddss xmm2,xmm1,dword ptr [rdx-14h]
000000013F5111C8 vmovss dword ptr [rdx-14h],xmm2
000000013F5111CD lea eax,[rbx+5]
000000013F5111D0 and eax,7FFh
000000013F5111D5 vmovss xmm0,dword ptr [rsi+rax*4]
000000013F5111DA vaddss xmm1,xmm0,dword ptr [rdi+rax*4]
000000013F5111DF vaddss xmm2,xmm1,dword ptr [rdx-10h]
000000013F5111E4 lea eax,[rbx+6]
000000013F5111E7 add ebx,8
000000013F5111EA vmovss dword ptr [rdx-10h],xmm2
000000013F5111EF and eax,7FFh
000000013F5111F4 vmovss xmm0,dword ptr [rsi+rax*4]
000000013F5111F9 vaddss xmm1,xmm0,dword ptr [rdi+rax*4]
000000013F5111FE vaddss xmm2,xmm1,dword ptr [rdx-0Ch]
000000013F511203 vmovss dword ptr [rdx-0Ch],xmm2
000000013F511208 sub r9,1
000000013F51120C jne Test4KAliasing2+0C0h (013F511120h)
000000013F511212 sub r8,1
000000013F511216 jne Test4KAliasing2+0B0h (013F511110h)
000000013F51121C rdtsc
对彼得对他的回答的评论/更新，我尝试过：
a[i] *= 1.234f;
b[i] += 4.321f;
没有显示问题。注意：在大多数此类尝试中，我尝试使用i = j + i + offset来改变i的偏移量，以便在以前的大多数尝试中看到能找到缓解该问题的偏移量。 （由于x86生锈，我仍在这里进行反汇编以了解地址生成）。
000000013F7D1104 cpuid
000000013F7D1106 rdtsc
000000013F7D1108 shl rdx,20h
000000013F7D110C or rax,rdx
000000013F7D110F mov edx,200h
000000013F7D1114 mov rbx,rax
000000013F7D1117 cmp rsi,r15
000000013F7D111A ja Test4KAliasing1+130h (013F7D1190h)
000000013F7D111C cmp rbp,r14
000000013F7D111F jb Test4KAliasing1+130h (013F7D1190h)
000000013F7D1121 lea rcx,[rsi+4]
000000013F7D1125 mov eax,100h
000000013F7D112A nop word ptr [rax+rax]
000000013F7D1130 vmulss xmm1,xmm6,dword ptr [rdi+rcx-4]
000000013F7D1136 vmovss dword ptr [rdi+rcx-4],xmm1
000000013F7D113C vaddss xmm1,xmm7,dword ptr [rcx-4]
000000013F7D1141 vmovss dword ptr [rcx-4],xmm1
000000013F7D1146 vmulss xmm1,xmm6,dword ptr [rcx+rdi]
000000013F7D114B vmovss dword ptr [rcx+rdi],xmm1
000000013F7D1150 vaddss xmm0,xmm7,dword ptr [rcx]
000000013F7D1154 vmovss dword ptr [rcx],xmm0
000000013F7D1158 vmulss xmm0,xmm6,dword ptr [rdi+rcx+4]
000000013F7D115E vmovss dword ptr [rdi+rcx+4],xmm0
000000013F7D1164 vaddss xmm0,xmm7,dword ptr [rcx+4]
000000013F7D1169 vmovss dword ptr [rcx+4],xmm0
000000013F7D116E vmulss xmm0,xmm6,dword ptr [rdi+rcx+8]
000000013F7D1174 vmovss dword ptr [rdi+rcx+8],xmm0
000000013F7D117A vaddss xmm0,xmm7,dword ptr [rcx+8]
000000013F7D117F vmovss dword ptr [rcx+8],xmm0
000000013F7D1184 lea rcx,[rcx+10h]
000000013F7D1188 sub rax,1
000000013F7D118C jne Test4KAliasing1+0D0h (013F7D1130h)
000000013F7D118E jmp Test4KAliasing1+1AEh (013F7D120Eh)
000000013F7D1190 vmovups xmm2,xmmword ptr [__xmm@3f9df3b63f9df3b63f9df3b63f9df3b6 (013F7EA0E0h)]
000000013F7D1198 vmovups xmm3,xmmword ptr [__xmm@408a45a2408a45a2408a45a2408a45a2 (013F7EA0F0h)]
000000013F7D11A0 lea rax,[rsi+10h]
000000013F7D11A4 mov ecx,40h
000000013F7D11A9 nop dword ptr [rax]
000000013F7D11B0 vmulps xmm1,xmm2,xmmword ptr [rdi+rax-10h]
000000013F7D11B6 vmovups xmmword ptr [rdi+rax-10h],xmm1
000000013F7D11BC vaddps xmm1,xmm3,xmmword ptr [rax-10h]
000000013F7D11C1 vmovups xmmword ptr [rax-10h],xmm1
000000013F7D11C6 vmulps xmm1,xmm2,xmmword ptr [rdi+rax]
000000013F7D11CB vmovups xmmword ptr [rdi+rax],xmm1
000000013F7D11D0 vaddps xmm1,xmm3,xmmword ptr [rax]
000000013F7D11D4 vmovups xmmword ptr [rax],xmm1
000000013F7D11D8 vmulps xmm1,xmm2,xmmword ptr [rdi+rax+10h]
000000013F7D11DE vmovups xmmword ptr [rdi+rax+10h],xmm1
000000013F7D11E4 vaddps xmm1,xmm3,xmmword ptr [rax+10h]
000000013F7D11E9 vmovups xmmword ptr [rax+10h],xmm1
000000013F7D11EE vmulps xmm1,xmm2,xmmword ptr [rdi+rax+20h]
000000013F7D11F4 vmovups xmmword ptr [rdi+rax+20h],xmm1
000000013F7D11FA vaddps xmm1,xmm3,xmmword ptr [rax+20h]
000000013F7D11FF vmovups xmmword ptr [rax+20h],xmm1
000000013F7D1204 lea rax,[rax+40h]
000000013F7D1208 sub rcx,1
000000013F7D120C jne Test4KAliasing1+150h (013F7D11B0h)
000000013F7D120E sub rdx,1
000000013F7D1212 jne Test4KAliasing1+0B7h (013F7D1117h)
000000013F7D1218 rdtsc
典型的计时运行时间：
a[i] *= 1.234f;
b[i] += 4.321f;
是：
time: 715 offset: 0
time: 647 offset: 1
time: 641 offset: 2
time: 703 offset: 3
time: 658 offset: 4
time: 657 offset: 5
time: 656 offset: 6
time: 657 offset: 7
time: 658 offset: 8
time: 657 offset: 9
time: 658 offset: 10
time: 653 offset: 11
time: 658 offset: 12
time: 652 offset: 13
time: 658 offset: 14
time: 657 offset: 15
time: 658 offset: 16
time: 656 offset: 17
time: 659 offset: 18
time: 656 offset: 19
time: 656 offset: 20
time: 656 offset: 21
time: 663 offset: 22
time: 657 offset: 23
time: 657 offset: 24
time: 704 offset: 25
time: 714 offset: 26
time: 657 offset: 27
time: 658 offset: 28
time: 658 offset: 29
time: 656 offset: 30
time: 656 offset: 31
time: 657 offset: 32
time: 658 offset: 33
time: 658 offset: 34
time: 656 offset: 35
time: 658 offset: 36
time: 658 offset: 37
time: 658 offset: 38
time: 658 offset: 39
time: 660 offset: 40
time: 660 offset: 41
time: 664 offset: 42
time: 656 offset: 43
time: 656 offset: 44
time: 658 offset: 45
time: 656 offset: 46
time: 656 offset: 47
time: 713 offset: 48
time: 658 offset: 49
time: 663 offset: 50
time: 662 offset: 51
time: 665 offset: 52
time: 663 offset: 53
time: 665 offset: 54
time: 658 offset: 55
time: 658 offset: 56
time: 658 offset: 57
time: 656 offset: 58
time: 657 offset: 59
time: 658 offset: 60
time: 658 offset: 61
time: 656 offset: 62
time: 666 offset: 63
time: 656 offset: 64
time: 658 offset: 65
time: 656 offset: 66
time: 657 offset: 67
time: 658 offset: 68
time: 658 offset: 69
time: 652 offset: 70
time: 658 offset: 71
time: 657 offset: 72
time: 658 offset: 73
time: 658 offset: 74
time: 656 offset: 75
time: 658 offset: 76
time: 665 offset: 77
time: 657 offset: 78
time: 656 offset: 79
time: 656 offset: 80
time: 666 offset: 81
time: 656 offset: 82
time: 702 offset: 83
time: 640 offset: 84
time: 640 offset: 85
time: 657 offset: 86
time: 657 offset: 87
time: 658 offset: 88
time: 658 offset: 89
time: 656 offset: 90
time: 657 offset: 91
time: 657 offset: 92
time: 657 offset: 93
time: 658 offset: 94
time: 662 offset: 95
time: 658 offset: 96
time: 656 offset: 97
time: 657 offset: 98
time: 663 offset: 99
time: 660 offset: 100
time: 663 offset: 101
time: 657 offset: 102
time: 656 offset: 103
time: 664 offset: 104
time: 659 offset: 105
time: 659 offset: 106
time: 658 offset: 107
time: 774 offset: 108
time: 707 offset: 109
time: 710 offset: 110
time: 658 offset: 111
time: 657 offset: 112
time: 661 offset: 113
time: 658 offset: 114
time: 656 offset: 115
time: 658 offset: 116
time: 657 offset: 117
time: 658 offset: 118
time: 660 offset: 119
time: 666 offset: 120
time: 657 offset: 121
time: 658 offset: 122
time: 651 offset: 123
time: 658 offset: 124
time: 657 offset: 125
time: 657 offset: 126
time: 658 offset: 127
time: 656 offset: 128
time: 658 offset: 129
time: 656 offset: 130
time: 658 offset: 131
time: 645 offset: 132
time: 640 offset: 133
time: 640 offset: 134
time: 659 offset: 135
time: 664 offset: 136
time: 658 offset: 137
time: 662 offset: 138
time: 656 offset: 139
time: 658 offset: 140
time: 656 offset: 141
time: 658 offset: 142
time: 660 offset: 143
time: 658 offset: 144
time: 658 offset: 145
time: 656 offset: 146
time: 657 offset: 147
time: 664 offset: 148
time: 656 offset: 149
time: 656 offset: 150
time: 658 offset: 151
time: 656 offset: 152
time: 668 offset: 153
time: 656 offset: 154
time: 656 offset: 155
time: 656 offset: 156
time: 658 offset: 157
time: 656 offset: 158
time: 658 offset: 159
time: 660 offset: 160
time: 658 offset: 161
time: 658 offset: 162
time: 658 offset: 163
time: 658 offset: 164
time: 656 offset: 165
time: 686 offset: 166
time: 656 offset: 167
time: 656 offset: 168
time: 658 offset: 169
time: 656 offset: 170
time: 658 offset: 171
time: 656 offset: 172
time: 656 offset: 173
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但是：我认为我犯了一个错误，现在已经发现了：
a[i] *= 1.234f;
b[j] += 4.321f;
现在是典型的计时运行：
time: 2794 offset: 0
time: 2737 offset: 1
time: 2655 offset: 2
time: 2748 offset: 3
time: 2605 offset: 4
time: 2730 offset: 5
time: 2665 offset: 6
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time: 2200 offset: 56
随着偏移量变大，可能会有大约20％的差异？
答案 0 :(得分：3)
您似乎已经使用/ O2和/ arch：AVX选项编译了代码。编译器已经展开了8次内部循环，您可以看到vmulss/vaddss/vmovss有8个序列。 a和b数组的地址分别存储在寄存器rdx和rdi中。第一条指令加载单个元素并将其乘以常数，第二条指令将结果与另一个数组中的相应元素相加，而第三条指令将结果存储到同一位置。考虑两个这样的序列：
000000013F251125 vmulss xmm1,xmm6,dword ptr [rdi+rcx*4]
000000013F25112A vaddss xmm2,xmm1,dword ptr [rdx-28h]
000000013F25112F vmovss dword ptr [rdx-28h],xmm2
000000013F251134 vmulss xmm1,xmm6,dword ptr [rdi+rax*4]
000000013F251139 vaddss xmm2,xmm1,dword ptr [rdx-24h]
000000013F25113E vmovss dword ptr [rdx-24h],xmm2
rcx和rax分别被初始化为零和一。 rdx初始化为数组a的基地址加0x28。在不失一般性的前提下，假设a和b的基地址分别为0x1000和0x2000。那么按程序顺序的内存访问顺序为：
load 0x2000
load 0x1000
store 0x1000
load 0x2004
load 0x1004
store 0x1004
是否有任何负载使以前的商店成为别名？请注意，您弄错了别名规则（请参见Peter的答案和此处的链接答案）。在load 0x2004和store 0x1000中，位5-11不同。在load 0x1004和store 0x1000中，位5-11相等。但是，访问不会重叠，因此没有别名。现在应该很容易明白为什么整个循环中没有负载会别名一个先前的商店。
如果将内循环主体更改为：
a[i] *= 1.234f;
b[j] += 4.321f;
然后来自每个数组的每对元素的序列变为vmulss/vmovss/vaddss/vmovss。前两个序列的内存访问配置文件是：
load 0x1000
store 0x1000
load 0x2000
store 0x1000
很明显，第二个加载别名第一个存储。由于j索引的计算方式，我尚不清楚在所有迭代中是否都会出现别名。但是在这种情况下它们确实存在。相反，使用索引i将确保所有迭代的每个vmulss/vmovss/vaddss/vmovss都有一个别名负载。
所以我不太确定为什么这不能显示问题。 产生的时间？
执行时间只能告诉您程序执行的速度，而不是原因。可观察到的4K别名损失取决于周围的代码和别名条件的总数。另外，对于不同的循环体，生成的二进制代码也不同，因此，如果执行时间发生了变化，则不一定意味着这是因为4K别名。是的，4K混叠可能是一个因素，甚至可能是一个主要因素，但是可能还有其他因素影响了执行时间。 top-down microarchitecture analysis methodology使您能够确定对执行时间影响最大的因素。
通常，确定4K别名是否发生的最佳方法是测量ld_blocks_partial.address_alias。您可以使用Processor Counter Monitor（在Windows，Linux和OSX上运行）来测量Intel PMU事件。我建议您这样做以验证我的分析是正确的。
答案 1 :(得分：2)
后12位为[11 : 0]位。第11位是第12位，因为我们从0开始计数。
CPU使用字节粒度检测加载/存储别名，而不仅仅是加载是否访问与较旧存储相同的缓存行。存储到array[1]不会减慢array[2]的负载；这对于性能确实是非常不利的，因为循环遍历一个数组并一次将每个元素RMW是一个很常见的模式。 （无需软件流水线就可以在存储位置之前加载多个元素。）
所以我认为您在这里没有遇到问题，因为您只是在从4k页面中的相同偏移量加载到后存储到位置。像这样简单的循环（不需要额外的跨步或偏移到另一个额外的页面中，只需在不同页面中使用两个数组即可。）
for (i = 0 ; i < limit ; i++) {
a[i] *= 1.234;
b[i] += 4.321; // load from the same offset we just wrote, but in another page
}
，并且编译器在加载a之前将asm存储到b，因为a和b相对于a具有相同的对齐方式，您会遇到问题。 4k页。
（如果编译器证明a != b，则编译器既可以在存储之前进行加载，也可以在运行执行该操作的循环版本之前发出要进行检查的代码。或者自动进行矢量化和/或展开）通过矢量宽度乘以展开因子来检查重叠。）
这不是一个完美的例子，但是从b来的负载依赖于a的存储，应该使乱序执行至少要努力工作才能隐藏这么大的延迟。
创建4k别名的另一种简便方法是从src = srcpage到dst = dstpage + 16或类似的东西，当然srcpage和dstpage都是页面对齐的。 dst[i]的存储类似于dstpage[i+16]（以字节为单位，而不是C元素的大小），因此在从dst[i]加载之前，将（按程序顺序）存储src[i+16]。当循环达到该i值时，负载将被4k别名阻止。
有关示例，请参见L1 memory bandwidth: 50% drop in efficiency using addresses which differ by 4096+64 bytes，使用@HadiBrais对包括IvyBridge（例如i7-3770k）在内的CPU进行性能分析。