RFR: 8245959: Extend String concat testing to account for folded constants

[Paul Sandoz]

Looks good.

Paul.

> On May 27, 2020, at 5:54 AM, Claes Redestad <claes.redestad at oracle.com> wrote:
> 
> Hi,
> 
> Since JDK-8222852 the default String concat strategy aggressively folds
> string constants into prepender method handles, which means an
> expression like foo + bar and one like "x" + foo + "y" + bar + "z" will
> have similar shape, but take slightly different paths through generated
> code.
> 
> This patch extends the ImplicitStringConcatShapes test to add more
> shape variants with surrounding String constants, which should improve
> coverage and put a bit more stress on the implementation strategy.
> 
> The changes of interest are in ImplicitStringConcatShapesTestGen -
> since that's what is used to generate ImplicitStringConcatShapes
> 
> Bug:    https://bugs.openjdk.java.net/browse/JDK-8245959
> Webrev: http://cr.openjdk.java.net/~redestad/8245959/open.00/
> 
> Testing: tier1
> 
> Thanks!
> 
> /Claes