[WebAssembly] Add another optimization idea to README.txt.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@261354 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/lib/Target/WebAssembly/README.txt b/lib/Target/WebAssembly/README.txt
index 68f902e..a2b35b2 100644 (file)
--- a/lib/Target/WebAssembly/README.txt
+++ b/lib/Target/WebAssembly/README.txt
@@ -100,3 +100,9 @@ WebAssembly registers are implicitly initialized to zero. Explicit zeroing is
 therefore often redundant and could be optimized away.
 
 //===---------------------------------------------------------------------===//
+
+Small indices may use smaller encodings than large indices.
+WebAssemblyRegRenumbering should sort registers according to their usage
+frequency to maximize the usage of smaller encodings.
+
+//===---------------------------------------------------------------------===//