Concat and CastString are equivalent in some cases
commit37dbf2523b0f30a5498ef6b540b486aafb8cb390
authorCatherine Gasnier <catg@fb.com>
Mon, 11 Dec 2017 13:42:51 +0000 (11 05:42 -0800)
committerHhvm Bot <hhvm-bot@users.noreply.github.com>
Mon, 11 Dec 2017 14:08:59 +0000 (11 06:08 -0800)
treee6f3f3339617268b10d22a12d44950cb4f7aa092
parent60c635bf9c530947abae569e40340f9d544c2e83
Concat and CastString are equivalent in some cases

Summary:
makes the 2 following sequences equivalent:
```
  String ""
  CGetL2 $b
  Concat
```
```
  CGetL $b
  CastString
```

Reviewed By: nbenton, vladima

Differential Revision: D6520127

fbshipit-source-id: 8beda9c4abe4a6e8199c81f25e42478cc31103d3
hphp/hack/src/hhbc/semdiff/hhbc_destruct.ml
hphp/hack/src/hhbc/semdiff/rhl.ml
hphp/test/hhcodegen_failing_tests_slow