Fixed '!NodePtr->isKnownSentinel()' assert caused by dereferencing end iterator when trying to const cast the iterator.

[martin.sherburn]

Summary

Fixed '!NodePtr->isKnownSentinel()' assert caused by dereferencing end iterator when trying to const cast the iterator.

Fixes bug in https://llvm.org/bugs/show_bug.cgi?id=30514

See https://reviews.llvm.org/rL279314 for more detail

[nhaehnle]

LGTM

[rivanvx]

LGTM as well

[martin.sherburn]

Sorry if this seems obvious but how do I get this committed to source control? This is my first patch so I don't have commit access. I use git mostly so if there is any way to submit a pull request or anything that's great but I'm happy to follow whatever is the usual approach.

[rivanvx]

You just wait until a maintainer picks it up.

[arsenm]

r290347

lib/Target/AMDGPU/SIMachineScheduler.cpp

 static MachineBasicBlock::iterator
 nextIfDebug(MachineBasicBlock::iterator I,
             MachineBasicBlock::const_iterator End) {
-  // Cast the return value to nonconst MachineInstr, then cast to an
-  // instr_iterator, which does not check for null, finally return a
-  // bundle_iterator.
-  return MachineBasicBlock::instr_iterator(
-    const_cast<MachineInstr*>(
-      &*nextIfDebug(MachineBasicBlock::const_iterator(I), End)));
+  for (; I != End; ++I) {
+    if (!I->isDebugValue())
+      break;
+  }
+  return I;
 }
 
 void SIScheduleBlockCreator::topologicalSort() {