Bug 1629496 - Correctly init wasm locals for functions with stack results r=lth

Ion functions with locals and stack results were inadvertantly skipping
a local, because they were considering the stack results pointer
argument as counting towards locals.

Differential Revision: https://phabricator.services.mozilla.com/D70797

--HG--
extra : moz-landing-system : lando

js/src/jit-test/tests/wasm/multi-value/regress-1629496.js

@@ -0,0 +1,9 @@
+let bytes = wasmTextToBinary(`
+  (module
+    (func $f (param) (result i32 i32)
+      (local i32)
+      (loop)
+      (i32.const 0)
+      (i32.const 1)))`);
+
+new WebAssembly.Instance(new WebAssembly.Module(bytes));

js/src/wasm/WasmIonCompile.cpp

@@ -184,7 +184,8 @@ class FunctionCompiler {
       return false;
     }
 
-    for (size_t i = args.length(); i < locals_.length(); i++) {
+    for (size_t i = args.lengthWithoutStackResults(); i < locals_.length();
+         i++) {
       MInstruction* ins = nullptr;
       switch (locals_[i].kind()) {
         case ValType::I32: