DFG Validation fails when performing a concatenation with only a single entry

[Oliver Hunt]

Fairly simple failure:

function f() {
    for (;;)`${1}`
}
f();

The issue is that we appear to be issuing a str_concat with a single child, which the DFG thinks is invalid. The obvious solutions are to either:
* don't emit str_concat from a single child template literal
* Have the DFG acknowledge this can happen

I think the former is the better option.

[Radar WebKit Bug Importer]

<rdar://problem/26775638>

[Oliver Hunt]

Created attachment 281211 [details]
Patch

[Saam Barati]

Comment on attachment 281211 [details]
Patch

View in context: https://bugs.webkit.org/attachment.cgi?id=281211&action=review

r=me

> Source/JavaScriptCore/tests/stress/template-literal.js:209
> +function testSingleNode() {

Can you also add other tests for valueOf, etc

[Oliver Hunt]

Comment on attachment 281211 [details]
Patch

View in context: https://bugs.webkit.org/attachment.cgi?id=281211&action=review

>> Source/JavaScriptCore/tests/stress/template-literal.js:209
>> +function testSingleNode() {
> 
> Can you also add other tests for valueOf, etc

Unrealted to this bug you mean? This bug is specifically because template literals would alway plant a strcat, even if there was only a single node.

[Oliver Hunt]

Committed r202015: <http://trac.webkit.org/changeset/202015>