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kripkenkripken
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Partial inlining via function splitting (WebAssembly#4152)
This PR helps with functions like this: function foo(x) { if (x) { .. lots of work here .. } } If "lots of work" is large enough, then we won't inline such a function. However, we may end up calling into the function only to get a false on that if and immediately exit. So it is useful to partially inline this function, basically by creating a split of it into a condition part that is inlineable function foo$inlineable(x) { if (x) { foo$outlined(); } } and an outlined part that is not inlineable: function foo$outlined(x) { .. lots of work here .. } We can then inline the inlineable part. That means that a call like foo(param); turns into if (param) { foo$outlined(); } In other words, we end up replacing a call and then a check with a check and then a call. Any time that the condition is false, this will be a speedup. The cost here is increased size, as we duplicate the condition into the callsites. For that reason, only do this when heavily optimizing for size. This is a 10% speedup on j2cl. This helps two types of functions there: Java class inits, which often look like "have I been initialized before? if not, do all this work", and also assertion methods which look like "if the input is null, throw an exception".
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Lines changed: 2921 additions & 623 deletions

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‎scripts/fuzz_opt.py‎

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@@ -176,6 +176,7 @@ def randomize_fuzz_settings():
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os.path.join('lit', 'passes', 'optimize-instructions-bulk-memory.wast'),
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os.path.join('lit', 'passes', 'optimize-instructions-ignore-traps.wast'),
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os.path.join('lit', 'passes', 'optimize-instructions-gc.wast'),
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os.path.join('lit', 'passes', 'inlining_splitting.wast'),
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]
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IMPORTANT_INITIAL_CONTENTS = [os.path.join(shared.get_test_dir('.'), t) for t in IMPORTANT_INITIAL_CONTENTS]
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‎src/ir/module-utils.h‎

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@@ -30,9 +30,12 @@ namespace wasm {
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namespace ModuleUtils {
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inline Function* copyFunction(Function* func, Module& out) {
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auto* ret = new Function();
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ret->name = func->name;
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// Copies a function into a module. If newName is provided it is used as the
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// name of the function (otherwise the original name is copied).
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inline Function*
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copyFunction(Function* func, Module& out, Name newName = Name()) {
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auto ret = std::make_unique<Function>();
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ret->name = newName.is() ? newName : func->name;
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ret->type = func->type;
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ret->vars = func->vars;
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ret->localNames = func->localNames;
@@ -43,8 +46,7 @@ inline Function* copyFunction(Function* func, Module& out) {
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ret->base = func->base;
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// TODO: copy Stack IR
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assert(!func->stackIR);
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out.addFunction(ret);
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return ret;
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return out.addFunction(std::move(ret));
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}
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inline Global* copyGlobal(Global* global, Module& out) {

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