[PHIElimination] Update the regression test for PR16508

Summary:
When PR16508 was solved (in rL185363) a regression test was
added as test/CodeGen/PowerPC/2013-07-01-PHIElimBug.ll.
I discovered that the test case no longer reproduced the
scenario from PR16508. This problem could have been amended
by adding an extra RUN line with "-O1" (or possibly "-O0"),
but instead I added a mir-reproducer
  test/CodeGen/PowerPC/2013-07-01-PHIElimBug.mir
to get a reproducer that is less sensitive to changes in
earlier passes (including O-level).

While being at it I also corrected a code comment in
PHIElimination::EliminatePHINodes that has been incorrect
since the related bugfix from rL185363.

Reviewers: MatzeB, hfinkel

Reviewed By: MatzeB

Subscribers: nemanjai, jsji, llvm-commits

Differential Revision: https://reviews.llvm.org/D52553

llvm-svn: 343416

1 files changed, 2 insertions, 3 deletions

diff --git a/llvm/lib/CodeGen/PHIElimination.cpp b/llvm/lib/CodeGen/PHIElimination.cpp
index 7a5c200..fc95cdf 100644
--- a/llvm/lib/CodeGen/PHIElimination.cpp
+++ b/llvm/lib/CodeGen/PHIElimination.cpp
@@ -197,12 +197,11 @@ bool PHIElimination::runOnMachineFunction(MachineFunction &MF) {
 /// EliminatePHINodes - Eliminate phi nodes by inserting copy instructions in
 /// predecessor basic blocks.
 bool PHIElimination::EliminatePHINodes(MachineFunction &MF,
-                                             MachineBasicBlock &MBB) {
+                                       MachineBasicBlock &MBB) {
   if (MBB.empty() || !MBB.front().isPHI())
     return false;   // Quick exit for basic blocks without PHIs.
 
-  // Get an iterator to the first instruction after the last PHI node (this may
-  // also be the end of the basic block).
+  // Get an iterator to the last PHI node.
   MachineBasicBlock::iterator LastPHIIt =
     std::prev(MBB.SkipPHIsAndLabels(MBB.begin()));