[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.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@247710 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/lib/CodeGen/ShrinkWrap.cpp b/lib/CodeGen/ShrinkWrap.cpp
index 7e2f15163cb4babc02390d66d49f0b7041aed2fc..c406c149c0071a5a8443f74c0f9f87b263ce02ab 100644 (file)
--- a/lib/CodeGen/ShrinkWrap.cpp
+++ b/lib/CodeGen/ShrinkWrap.cpp
@@ -309,6 +309,14 @@ void ShrinkWrap::updateSaveRestorePoints(MachineBasicBlock &MBB) {
         }
       }
       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.