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Mention opcode name syntax for alignment #342

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lukewagner merged 1 commit into from
Sep 14, 2015
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Mention opcode name syntax for alignment #342

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6 changes: 6 additions & 0 deletions AstSemantics.md
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Expand Up @@ -149,6 +149,12 @@ Each linear memory access operation also has an immediate positive integer power
of 2 alignment attribute. An alignment value which is the same as the memory
attribute size is considered to be a *natural* alignment.

The linear memory operation names listed above specify natural alignment.
To specify unnatural alignment, the opcode name can be suffixed with `/n` for
`n` any integer power of 2. For example, `float64.load/2` specifies a `float32`
load with 2-byte alignment; `int32.load16_s/1` specifies a signed 2-byte load
that is unaligned (1-byte aligned).
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@jfbastien jfbastien Sep 11, 2015

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I think this is a better fit for text format, since it's implicit in the bytecode format?

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@lukewagner lukewagner Sep 11, 2015

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Do you mean that you think this para should go in TextFormat.md? I kinda see that point, but opcode names are not just a detail of the text format; they also show up in the SExpr language as the names of AST nodes and will show up in the module local opcode table (which is part of the binary format). AstSemantics is sortof the central hub, so I think it makes sense for it to define the names of opcodes.

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@jfbastien jfbastien Sep 11, 2015

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Yeah, but I see your point too. lgtm then :-)


The alignment applies to the effective address and not merely the address operand,
i.e. the immediate offset is taken into account when considering alignment.

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