Use hints when generating fresh labels in IRBuilder (#7086)

IRBuilder often has to generate new label names for blocks and other
scopes. Previously it would generate each new name by starting with
"block" or "label" and incrementing a suffix until finding a fresh name,
but this made name generation quadratic in the number of names to
generate.

To spend less time generating names, track a hint index at which to
start looking for a fresh name and increment it every time a name is
generated. This speeds up a version of the binary parser that uses
IRBuilder by about 15%.

1 files changed, 4 insertions, 2 deletions

diff --git a/src/wasm/wasm-ir-builder.cpp b/src/wasm/wasm-ir-builder.cpp
index 5253c91ee..a73c7f2ac 100644
--- a/src/wasm/wasm-ir-builder.cpp
+++ b/src/wasm/wasm-ir-builder.cpp
@@ -987,6 +987,8 @@ Result<> IRBuilder::visitEnd() {
       EHUtils::handleBlockNestedPops(func, wasm);
     }
     this->func = nullptr;
+    blockHint = 0;
+    labelHint = 0;
   } else if (auto* block = scope.getBlock()) {
     assert(*expr == block);
     block->name = scope.label;
@@ -1073,9 +1075,9 @@ Result<Name> IRBuilder::getLabelName(Index label, bool forDelegate) {
   if (!scopeLabel) {
     // The scope does not already have a name, so we need to create one.
     if ((*scope)->getBlock()) {
-      scopeLabel = makeFresh("block");
+      scopeLabel = makeFresh("block", blockHint++);
     } else {
-      scopeLabel = makeFresh("label");
+      scopeLabel = makeFresh("label", labelHint++);
     }
   }
   if (!forDelegate) {