[llvm] r247710 - [ShrinkWrapping] Fix an infinite loop while looking for restore point.

[Quentin Colombet via llvm-commits]

Author: qcolombet
Date: Tue Sep 15 13:19:39 2015
New Revision: 247710

URL: http://llvm.org/viewvc/llvm-project?rev=247710&view=rev
Log:
[ShrinkWrapping] Fix an infinite loop while looking for restore point.
This may happen when the input program itself contains an infinite loop with no
exit block. In that case, we would fail to find a block post-dominating the loop
such that this block is outside of the loop.

This fixes PR24823.
Working on reducing the test case.

Modified:
    llvm/trunk/lib/CodeGen/ShrinkWrap.cpp

Modified: llvm/trunk/lib/CodeGen/ShrinkWrap.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/CodeGen/ShrinkWrap.cpp?rev=247710&r1=247709&r2=247710&view=diff
==============================================================================
--- llvm/trunk/lib/CodeGen/ShrinkWrap.cpp (original)
+++ llvm/trunk/lib/CodeGen/ShrinkWrap.cpp Tue Sep 15 13:19:39 2015
@@ -309,6 +309,14 @@ void ShrinkWrap::updateSaveRestorePoints
         }
       }
       else {
+        // If the loop does not exit, there is no point in looking
+        // for a post-dominator outside the loop.
+        SmallVector<MachineBasicBlock*, 4> ExitBlocks;
+        MLI->getLoopFor(Restore)->getExitingBlocks(ExitBlocks);
+        if (ExitBlocks.empty()) {
+          Restore = nullptr;
+          break;
+        }
         // Push Restore outside of this loop if immediate post-dominator is
         // different from restore block. If immediate post-dominator is not
         // different, bail out.