[LLVMdev] RFC: X86InstrFormats.td Refactoring

[David Greene]

There is some redundancy at the instruction format level in the x86 .td files.  
For example, in X86InstrFormats.td:

// SSE1 Instruction Templates:
// 
//   SSI   - SSE1 instructions with XS prefix.

class SSI<bits<8> o, Format F, dag outs, dag ins, string asm, list<dag> 
pattern>
      : I<o, F, outs, ins, asm, pattern>, XS, Requires<[HasSSE1]>;

// SSE3 Instruction Templates:
//   S3SI   - SSE3 instructions with XSrefix.

class S3SI<bits<8> o, Format F, dag outs, dag ins, string asm, list<dag> 
pattern>
      : I<o, F, outs, ins, asm, pattern>, XS, Requires<[HasSSE3]>;

The only difference here is the parameter to Requires.  There are many more 
examples and this gets worse with AVX.

I'd like to propose a refactoring that looks something like this:

// SSE Instruction Templates:
//
//  SSI - SSE Instructions with XS prefix

class SSI<bits<8> o, Format F, dag outs, dag ins, string asm, list<dag> 
pattern>
      : I<o, F, outs, ins, asm, pattern>, XS;

/./ SSE1 Instruction Templates
//
//  S1SI - SSE1 instructions with Xs prefix

class S1SI<bits<8> o, Format F, dag outs, dag ins, string asm, list<dag> 
pattern>
      : SSI<o, F, outs, ins, asm, pattern>, Requires<HasSSE1>;

This way we can reuse the SSI class and hide encoding details for many SSE 
levels and AVX.

Sound good?

                                             -Dave