Rename "Literals" to "Immediates" and spell out operators.

[sunfishcode]

"Immediate" is the more common term to use in assembly languages.

Also, remove a broken link to the binary encoding page. The binary
encoding is not yet determined, but AstSemantics.md doesn't need to
reference it right now anyway.

[rossberg]

I don't think literals are the same as immediates. An immediate in assembly language is part of a given instruction. But the literal expressions in Wasm are not part of the surrounding opcode, they are (at least logically) their own, stand-alone instructions, "loading" constants. Moreover, they may or may not be implemented with CPU instructions having the constant as an immediate (for example, a float constant may need to be loaded from memory on some architectures, I believe; some constants can also be loaded from special registers, or be produced via specific opcodes).

So I disagree with this change; IMHO it is conflating abstraction levels.

[titzer]

On Tue, Sep 29, 2015 at 12:55 PM, rossberg-chromium <
notifications@github.com> wrote:

I don't think literals are the same as immediates. An immediate in
assembly language is part of a given instruction. But the literal
expressions in Wasm are not part of the surrounding opcode, they are (at
least logically) their own, stand-alone instructions, "loading" constants.
Moreover, they may or may not be implemented with CPU instructions having
the constant as an immediate (for example, a float constant may need to be
loaded from memory on some architectures, I believe; some constants can
also be loaded from special registers, or be produced via specific opcodes).

So I disagree with this change; IMHO it is conflating abstraction levels.

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[lukewagner]

FWIW, I do think we have immediates, in the form of the integer operands to AST nodes (e.g., the index of get_local or the alignment of load).

[sunfishcode]

That works for me. Immediates are things that are "part of the opcode", and we can call our "load immediate" instructions "literals" to avoid ambiguity. I submitted WebAssembly/spec#88 to implement this in the spec.