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, 4 deletions

diff --git a/test/wasm2js/labels.2asm.js b/test/wasm2js/labels.2asm.js
index ac2978300..431e172d9 100644
--- a/test/wasm2js/labels.2asm.js
+++ b/test/wasm2js/labels.2asm.js
@@ -143,10 +143,6 @@ function asmFunc(imports) {
    break label;
   }
   i = i + 1 | 0;
-  label0 : {
-   break label0;
-  }
-  i = i + 1 | 0;
   label1 : {
    break label1;
   }
@@ -159,6 +155,10 @@ function asmFunc(imports) {
    break label3;
   }
   i = i + 1 | 0;
+  label4 : {
+   break label4;
+  }
+  i = i + 1 | 0;
   return i | 0;
  }