diff options
Diffstat (limited to 'src')
| -rw-r--r-- | src/passes/Precompute.cpp | 6 | ||||
| -rw-r--r-- | src/passes/SimplifyGlobals.cpp | 22 |
2 files changed, 22 insertions, 6 deletions
diff --git a/src/passes/Precompute.cpp b/src/passes/Precompute.cpp index 5baf2331f..89e618ab3 100644 --- a/src/passes/Precompute.cpp +++ b/src/passes/Precompute.cpp @@ -799,9 +799,11 @@ private: if (type.isFunction()) { return true; } - // We can emit a StringConst for a string constant. + // We can emit a StringConst for a string constant in principle, but we do + // not want to as that might cause more allocations to happen. See similar + // code in SimplifyGlobals. if (type.isString()) { - return true; + return false; } // All other reference types cannot be precomputed. Even an immutable GC // reference is not currently something this pass can handle, as it will diff --git a/src/passes/SimplifyGlobals.cpp b/src/passes/SimplifyGlobals.cpp index 3baec4409..a7d8c3487 100644 --- a/src/passes/SimplifyGlobals.cpp +++ b/src/passes/SimplifyGlobals.cpp @@ -52,6 +52,20 @@ namespace wasm { namespace { +// Checks if an expression is a constant, and one that we can copy without +// downsides. This is the set of constant values that we will inline from +// globals. +bool isCopyableConstant(Expression* curr) { + // Anything that is truly constant is suitable for us, *except* for string + // constants, which in VMs may be implemented not as a constant but as an + // allocation. We prefer to keep string.const in globals where any such + // allocation only happens once (note that that makes them equivalent to + // strings imported from JS, which would be in imported globals, which are + // similarly not optimizable). + // TODO: revisit this if/when VMs implement and optimize string.const. + return Properties::isConstantExpression(curr) && !curr->is<StringConst>(); +} + struct GlobalInfo { // Whether the global is imported and exported. bool imported = false; @@ -358,7 +372,7 @@ struct ConstantGlobalApplier void visitExpression(Expression* curr) { if (auto* set = curr->dynCast<GlobalSet>()) { - if (Properties::isConstantExpression(set->value)) { + if (isCopyableConstant(set->value)) { currConstantGlobals[set->name] = getLiteralsFromConstExpression(set->value); } else { @@ -369,7 +383,7 @@ struct ConstantGlobalApplier // Check if the global is known to be constant all the time. if (constantGlobals->count(get->name)) { auto* global = getModule()->getGlobal(get->name); - assert(Properties::isConstantExpression(global->init)); + assert(isCopyableConstant(global->init)); replaceCurrent(ExpressionManipulator::copy(global->init, *getModule())); replaced = true; return; @@ -671,7 +685,7 @@ struct SimplifyGlobals : public Pass { // go, as well as applying them where possible. for (auto& global : module->globals) { if (!global->imported()) { - if (Properties::isConstantExpression(global->init)) { + if (isCopyableConstant(global->init)) { constantGlobals[global->name] = getLiteralsFromConstExpression(global->init); } else { @@ -695,7 +709,7 @@ struct SimplifyGlobals : public Pass { NameSet constantGlobals; for (auto& global : module->globals) { if (!global->mutable_ && !global->imported() && - Properties::isConstantExpression(global->init)) { + isCopyableConstant(global->init)) { constantGlobals.insert(global->name); } } |