[llvm] [VPlan] Add simple driver option to run some individual transforms. (PR #178522)

[Andrei Elovikov via llvm-commits]

================
@@ -0,0 +1,40 @@
+; REQUIRES: asserts
+
+; Test the remove-dead-recipes VPlan transform that removes unused recipes.
+
+; RUN: opt -passes=loop-vectorize -vplan-test-transform='widen-from-metadata,remove-dead-recipes,print' -disable-output %s 2>&1 | FileCheck %s
----------------
eas wrote:

I somewhat disagree. Having a comment before the pipeline makes it easier to understand why those specific transforms were chosen. With the current order it's one continuous flow of reading. If we reorder, then one would have skip the RUN line, read the comment, get back to the RUN line when reading this file.

Also, I think about 25% of "REQURIES: asserts" in the vectorizer tests are on the first line:

```
$ grep -n -r -e REQUIRES . | grep ".ll:1:; REQUIRES:" | wc -l
85
$ grep -n -r -e REQUIRES . | wc -l
283
```

https://github.com/llvm/llvm-project/pull/178522