[Parser] Re-use blocks instead of wrapping where possible (#6552)

When the input has branches to block scope, IR builder generally has to add a
wrapper block with a label name for the branch to target. To reduce the parsed
IR size, add a special case for when the wrapped expression is already an
unnamed block. In that case we can simply add the label to the existing block
instead of creating a new wrapper block.

1 files changed, 11 insertions, 6 deletions

diff --git a/src/wasm/wasm-ir-builder.cpp b/src/wasm/wasm-ir-builder.cpp
index 6322a5786..91e990180 100644
--- a/src/wasm/wasm-ir-builder.cpp
+++ b/src/wasm/wasm-ir-builder.cpp
@@ -929,13 +929,18 @@ Result<> IRBuilder::visitEnd() {
   auto maybeWrapForLabel = [&](Expression* curr) -> Expression* {
     bool isTry = scope.getTry() || scope.getCatch() || scope.getCatchAll();
     auto& label = isTry ? scope.branchLabel : scope.label;
-    if (label) {
-      return builder.makeBlock(label,
-                               {curr},
-                               scope.labelUsed ? originalScopeType
-                                               : scope.getResultType());
+    if (!label) {
+      return curr;
     }
-    return curr;
+    auto blockType =
+      scope.labelUsed ? originalScopeType : scope.getResultType();
+    // We can re-use unnamed blocks instead of wrapping them.
+    if (auto* block = curr->dynCast<Block>(); block && !block->name) {
+      block->name = label;
+      block->type = blockType;
+      return block;
+    }
+    return builder.makeBlock(label, {curr}, blockType);
   };
 
   if (auto* func = scope.getFunction()) {