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Optimize NOPs

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This commit is contained in:
Tillmann Karras
2014-04-23 21:15:09 +02:00
parent 65e0579d9f
commit 957649b7af
2 changed files with 55 additions and 15 deletions
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68
Source/Core/Common/x64Emitter.cpp
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@ -515,23 +515,63 @@ void XEmitter::INT3() {Write8(0xCC);}
void XEmitter::RET() {Write8(0xC3);}
void XEmitter::RET_FAST() {Write8(0xF3); Write8(0xC3);} //two-byte return (rep ret) - recommended by AMD optimization manual for the case of jumping to a ret
void XEmitter::NOP(int count)
// The first sign of decadence: optimized NOPs.
void XEmitter::NOP(int size)
{
// TODO: look up the fastest nop sleds for various sizes
int i;
switch (count) {
case 1:
Write8(0x90);
break;
case 2:
Write8(0x66);
Write8(0x90);
break;
default:
for (i = 0; i < count; i++) {
while (true)
{
switch (size)
{
case 0:
return;
case 1:
Write8(0x90);
return;
case 2:
Write8(0x66); Write8(0x90);
return;
case 3:
Write8(0x0F); Write8(0x1F); Write8(0x00);
return;
case 4:
Write8(0x0F); Write8(0x1F); Write8(0x40); Write8(0x00);
return;
case 5:
Write8(0x0F); Write8(0x1F); Write8(0x44); Write8(0x00);
Write8(0x00);
return;
case 6:
Write8(0x66); Write8(0x0F); Write8(0x1F); Write8(0x44);
Write8(0x00); Write8(0x00);
return;
case 7:
Write8(0x0F); Write8(0x1F); Write8(0x80); Write8(0x00);
Write8(0x00); Write8(0x00); Write8(0x00);
return;
case 8:
Write8(0x0F); Write8(0x1F); Write8(0x84); Write8(0x00);
Write8(0x00); Write8(0x00); Write8(0x00); Write8(0x00);
return;
case 9:
Write8(0x66); Write8(0x0F); Write8(0x1F); Write8(0x84);
Write8(0x00); Write8(0x00); Write8(0x00); Write8(0x00);
Write8(0x00);
return;
case 10:
Write8(0x66); Write8(0x66); Write8(0x0F); Write8(0x1F);
Write8(0x84); Write8(0x00); Write8(0x00); Write8(0x00);
Write8(0x00); Write8(0x00);
return;
default:
// Even though x86 instructions are allowed to be up to 15 bytes long,
// AMD advises against using NOPs longer than 11 bytes because they
// carry a performance penalty on CPUs older than AMD family 16h.
Write8(0x66); Write8(0x66); Write8(0x66); Write8(0x0F);
Write8(0x1F); Write8(0x84); Write8(0x00); Write8(0x00);
Write8(0x00); Write8(0x00); Write8(0x00);
size -= 11;
continue;
}
break;
}
}