[PATCH] SimplifyCFG: don't remove unreachable defaults from switch instructions; exploit them instead!

[David Majnemer]

================
Comment at: lib/Transforms/Utils/SimplifyCFG.cpp:3228
@@ -3236,3 +3227,3 @@
   // If NumCases overflowed, then all possible values jump to the successor.
-  if (NumCases->isNullValue() && SI->getNumCases() != 0)
+  if (NumCases->isNullValue() && ContiguousCases->size() != 0)
     Cmp = ConstantInt::getTrue(SI->getContext());
----------------
`!ContiguousCases->empty()`

================
Comment at: lib/Transforms/Utils/SimplifyCFG.cpp:3247
@@ +3246,3 @@
+      }
+      while (TrueWeight > UINT_MAX || FalseWeight > UINT_MAX) {
+        TrueWeight /= 2;
----------------
I'd go with `UINT32_MAX` to match the casts bellow.

================
Comment at: lib/Transforms/Utils/SimplifyCFG.cpp:4202
@@ -4197,3 +4201,3 @@
     SI->getDefaultDest()->removePredecessor(SI->getParent(),
-                                            true/*DontDeleteUselessPHIs*/);
+                                            true /*DontDeleteUselessPHIs*/);
   } else {
----------------
  /*DontDeleteUselessPHIs=*/true

http://reviews.llvm.org/D6471