SmallVector (#1912)

Trying to refactor the code to be simpler and less redundant, I ran into some perf issues that it seems like a small vector, with fixed-size storage and optional additional storage as needed, might help with. This implements that class and uses it in a few places.

This seems to help, I see some 1-2% fewer instructions and cycles in `perf stat`, but it's hard to tell if it really makes a noticeable difference.

1 files changed, 1 insertions, 1 deletions

diff --git a/src/passes/SimplifyLocals.cpp b/src/passes/SimplifyLocals.cpp
index 91f0f8d4f..a4931f06c 100644
--- a/src/passes/SimplifyLocals.cpp
+++ b/src/passes/SimplifyLocals.cpp
@@ -271,7 +271,7 @@ struct SimplifyLocals : public WalkerPass<LinearExecutionWalker<SimplifyLocals<a
 
   // a full expression stack is used when !allowNesting, so that we can check if
   // a sink would cause nesting
-  std::vector<Expression*> expressionStack;
+  ExpressionStack expressionStack;
 
   static void visitPre(SimplifyLocals<allowTee, allowStructure, allowNesting>* self, Expression** currp) {
     Expression* curr = *currp;