[PATCH] D21665: [LoopSimplify] Update LCSSA after separating nested loops.

[Sanjoy Das via llvm-commits]

sanjoy added inline comments.

================
Comment at: lib/Transforms/Utils/LoopSimplify.cpp:353
@@ +352,3 @@
+      for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
+        Instruction *V = dyn_cast<Instruction>(PN->getIncomingValue(i));
+        if (!V || !L->contains(V))
----------------
s/V/I/

================
Comment at: lib/Transforms/Utils/LoopSimplify.cpp:370
@@ +369,3 @@
+            NewPN->addIncoming(V, PredBB);
+          PN->setIncomingValue(i, NewPN);
+          break;
----------------
What if you have

```
loop:
  %iv = phi [ 0, %entry ] [ %iv, (%loop, %left, %right)],  [ %iv.inc, %outer ]
  %iv.inc = %iv + 1
  switch(condition), %left, %right, %loop

left:
  br condition, %outer, %loop

right:
  br condition, %outer, %loop

outer:
  br %loop
```

then the separated loop structure will be

```
outer_header:
  %iv = [ 0, %entry ] , [ %iv.inc, %outer ]
  br loop

loop:
  %iv.inc = %iv + 1
  switch(condition), %left, %right, %loop

left:
  br condition, %outer, %loop

right:
  br condition, %outer, %loop

outer:
  br %loop
```

Now %iv.inc is live out of the inner loop and none of the inner loop
exits (%left, %right) dominate %outer.


http://reviews.llvm.org/D21665