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Optimize NOPs
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@ -515,23 +515,63 @@ void XEmitter::INT3() {Write8(0xCC);}
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void XEmitter::RET() {Write8(0xC3);}
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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
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void XEmitter::NOP(int count)
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// The first sign of decadence: optimized NOPs.
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void XEmitter::NOP(int size)
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{
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// TODO: look up the fastest nop sleds for various sizes
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int i;
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switch (count) {
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case 1:
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Write8(0x90);
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break;
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case 2:
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Write8(0x66);
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Write8(0x90);
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break;
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default:
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for (i = 0; i < count; i++) {
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while (true)
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{
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switch (size)
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{
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case 0:
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return;
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case 1:
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Write8(0x90);
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return;
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case 2:
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Write8(0x66); Write8(0x90);
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return;
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case 3:
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Write8(0x0F); Write8(0x1F); Write8(0x00);
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return;
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case 4:
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Write8(0x0F); Write8(0x1F); Write8(0x40); Write8(0x00);
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return;
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case 5:
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Write8(0x0F); Write8(0x1F); Write8(0x44); Write8(0x00);
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Write8(0x00);
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return;
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case 6:
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Write8(0x66); Write8(0x0F); Write8(0x1F); Write8(0x44);
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Write8(0x00); Write8(0x00);
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return;
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case 7:
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Write8(0x0F); Write8(0x1F); Write8(0x80); Write8(0x00);
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Write8(0x00); Write8(0x00); Write8(0x00);
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return;
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case 8:
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Write8(0x0F); Write8(0x1F); Write8(0x84); Write8(0x00);
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Write8(0x00); Write8(0x00); Write8(0x00); Write8(0x00);
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return;
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case 9:
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Write8(0x66); Write8(0x0F); Write8(0x1F); Write8(0x84);
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Write8(0x00); Write8(0x00); Write8(0x00); Write8(0x00);
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Write8(0x00);
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return;
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case 10:
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Write8(0x66); Write8(0x66); Write8(0x0F); Write8(0x1F);
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Write8(0x84); Write8(0x00); Write8(0x00); Write8(0x00);
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Write8(0x00); Write8(0x00);
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return;
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default:
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// Even though x86 instructions are allowed to be up to 15 bytes long,
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// AMD advises against using NOPs longer than 11 bytes because they
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// carry a performance penalty on CPUs older than AMD family 16h.
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Write8(0x66); Write8(0x66); Write8(0x66); Write8(0x0F);
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Write8(0x1F); Write8(0x84); Write8(0x00); Write8(0x00);
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Write8(0x00); Write8(0x00); Write8(0x00);
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size -= 11;
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continue;
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}
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break;
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}
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}
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