Bug 161948 – TaggedTemplateString function calls should emit tail position calls

• Status: RESOLVED
• Resolution: FIXED
• Component: JavaScriptCore

[Joseph Pecoraro]

Summary:
TaggedTemplateString function calls should emit tail position calls.

Test:
<script>
"use strict";
function tag() {
    debugger;
    return "test";
}

function templateTagPath() { return tag`test`; }
function testTemplateTagPath() { return templateTagPath(); }

function normalPath() { return tag(); }
function testNormalPath() { return normalPath(); }

testNormalPath();
testTemplateTagPath();
</script>

Steps to reproduce:
1. Inspect test page
2. Reload (to hit breakpoints)
3. First breakpoint is in normal function call path
  => normalPath and testNormalPath are shown to be tail deleted frames in the debugger sidebar
4. Continue
5. Second pause is in tagged template string function call path
  => testTemplateTagPath is shown to be tail deleted but templateTagPath is not. It should be!

Spec:
https://tc39.github.io/ecma262/#sec-tagged-templates-runtime-semantics-evaluation

> MemberExpression:MemberExpressionTemplateLiteral
> 
>   1. Let tagRef be the result of evaluating MemberExpression.
>   2. Let thisCall be this MemberExpression.
>   3. Let tailCall be IsInTailPosition(thisCall).
>   4. Return ? EvaluateCall(tagRef, TemplateLiteral, tailCall).
> 
> CallExpression:CallExpressionTemplateLiteral
> 
>   1. Let tagRef be the result of evaluating CallExpression.
>   2. Let thisCall be this CallExpression.
>   3. Let tailCall be IsInTailPosition(thisCall).
>   4. Return ? EvaluateCall(tagRef, TemplateLiteral, tailCall).

[Joseph Pecoraro]

Should be as simple as changing the emitCall to emitCallInTailPosition. I'm doing a build now.

[Joseph Pecoraro]

This is tested by:
test262/test/language/expressions/tagged-template/tco-call.js

Not sure if I need to do anything about that. I'll just add to the existing simple test for checking tail calls.

[Joseph Pecoraro]

Created attachment 288786 [details]
[PATCH] Proposed Fix

[Joseph Pecoraro]

Comment on attachment 288786 [details]
[PATCH] Proposed Fix

I should be able to update the test262.yaml if I can verify the single test succeeds now.

[Joseph Pecoraro]

Created attachment 288787 [details]
[PATCH] Proposed Fix

[Yusuke Suzuki]

Comment on attachment 288787 [details]
[PATCH] Proposed Fix

r=me

[WebKit Commit Bot]

Comment on attachment 288787 [details]
[PATCH] Proposed Fix

Clearing flags on attachment: 288787

Committed r205916: <http://trac.webkit.org/changeset/205916>

[WebKit Commit Bot]

All reviewed patches have been landed.  Closing bug.