[WebAssembly] Enable register coloring and register stackifying.

This also takes the push/pop syntax another step forward, introducing stack
slot numbers to make it easier to see how expressions are

[WebAssembly] Enable register coloring and register stackifying.

This also takes the push/pop syntax another step forward, introducing stack
slot numbers to make it easier to see how expressions are connected. For
example, the value pushed in $push7 is popped in $pop7.

And, this begins an experiment with making get_local and set_local implicit
when an operation directly uses or defines a register. This greatly reduces
clutter. If this experiment succeeds, it may make sense to do this for
const instructions as well.

And, this introduces more special code for ARGUMENTS; hopefully this code
will soon be obviated by proper support for live-in virtual registers.

llvm-svn: 253465

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[WebAssembly] Introduce a new pseudo-operand for unused expression results.

llvm-svn: 252975

[WebAssembly] Reapply r252858, with svn add for the new file.

Switch to MC for instruction printing.

This encompasses several changes which are all interconnected:
- Use the MC framework for print

[WebAssembly] Reapply r252858, with svn add for the new file.

Switch to MC for instruction printing.

This encompasses several changes which are all interconnected:
- Use the MC framework for printing almost all instructions.
- AsmStrings are now live.
- This introduces an indirection between LLVM vregs and WebAssembly registers,
and a new pass, WebAssemblyRegNumbering, for computing a basic the mapping.
This addresses some basic issues with argument registers and unused registers.
- The way ARGUMENT instructions are handled no longer generates redundant
get_local+set_local for every argument.

This also changes the assembly syntax somewhat; most notably, MC's printing
does not use sigils on label names, so those are no longer present, and
push/pop now have a sigil to keep them unambiguous.

The usage of set_local/get_local/$push/$pop will continue to evolve
significantly. This patch is just one step of a larger change.

llvm-svn: 252910

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