1527563 - Remove defunct nested-call optimisation in WasmIonCompile.cpp

Status: RESOLVED FIXED

(Core :: JavaScript: WebAssembly, enhancement)

Description

[Julian Seward [:jseward]]

Translation of wasm into MIR is currently set up to handle multiple nested
function call instances simultaneously, using a stack of CallCompileState
records to keep track of the per-open-call state. This is an optimisation
intended to allow interleaved evaluation and pushing of stack-resident
outbound arguments. However, this was predicated on the assumption of
pre-order Wasm encoding, which is no longer valid -- encoding is post-order.

The compiler's operand (wasm) stack tracks MIR value nodes, which are by
definition already evaluated -- it doesn't track unevaluated expression trees.
Consequently, by the time we arrive at a wasm call instruction, we have to
hand the MIR nodes for all the arguments, so the possibility of evaluating
arguments whilst marshalling the arguments no longer exists.

Comment 1

[Julian Seward [:jseward]]

Attachment: bug1527563-simplify-calls-1.diff

Comment 2

[Luke Wagner [:luke]]

Comment on attachment 9043550 [details] [diff] [review]
bug1527563-simplify-calls-1.diff

Review of attachment 9043550 [details] [diff] [review]:
-----------------------------------------------------------------

Thanks!  Nice to disentangle lineOrBytecode as well.

::: js/src/wasm/WasmIonCompile.cpp
@@ +71,5 @@
>    friend class FunctionCompiler;
>  
>   public:
> +  // JRS FIXME: why pass in |f| here?  Can this be rm'd?
> +  CallCompileState(FunctionCompiler& f) {}

Kill it; it was probably used to pluck out some field value at some time in the past.

Comment 3

[Julian Seward [:jseward]]

Attachment: bug1527563-simplify-calls-3.diff

This is the same as the previous version, but rebased to m-c current
and with the removal in comment 2 actioned.

Comment 4

[Luke Wagner [:luke]]

Comment on attachment 9043914 [details] [diff] [review]
bug1527563-simplify-calls-3.diff

Review of attachment 9043914 [details] [diff] [review]:
-----------------------------------------------------------------

Nice!

Comment 5

[Pulsebot]

Pushed by [e-mail]:
https://hg.mozilla.org/integration/mozilla-inbound/rev/cd56d5e49b75
Remove defunct nested-call optimisation in WasmIonCompile.cpp.  r=luke.

Comment 6

[Cosmin Sabou [:CosminS]]

https://hg.mozilla.org/mozilla-central/rev/cd56d5e49b75