[MachineOutliner] NFC: Add debug output to overlap pruning code

This had no debug output. Since it was committed as NFC, it had no testcase.

The me of today was nerdsniped by the me of 6 years ago and decided that this
ought to have a testcase and some debug output.

llvm/lib/CodeGen/MachineOutliner.cpp

@@ -572,11 +572,19 @@ void MachineOutliner::findCandidates(
   // First, find all of the repeated substrings in the tree of minimum length
   // 2.
   std::vector<Candidate> CandidatesForRepeatedSeq;
+  LLVM_DEBUG(dbgs() << "*** Discarding overlapping candidates *** \n");
+  LLVM_DEBUG(
+      dbgs() << "Searching for overlaps in all repeated sequences...\n");
   for (const SuffixTree::RepeatedSubstring &RS : ST) {
     CandidatesForRepeatedSeq.clear();
     unsigned StringLen = RS.Length;
+    LLVM_DEBUG(dbgs() << "  Sequence length: " << StringLen << "\n");
+    // Debug code to keep track of how many candidates we removed.
+#ifndef NDEBUG
+    unsigned NumDiscarded = 0;
+    unsigned NumKept = 0;
+#endif
     for (const unsigned &StartIdx : RS.StartIndices) {
-      unsigned EndIdx = StartIdx + StringLen - 1;
       // Trick: Discard some candidates that would be incompatible with the
       // ones we've already found for this sequence. This will save us some
       // work in candidate selection.
@@ -598,23 +606,39 @@ void MachineOutliner::findCandidates(
       // That is, one must either
       // * End before the other starts
       // * Start after the other ends
-      if (all_of(CandidatesForRepeatedSeq, [&StartIdx,
-                                            &EndIdx](const Candidate &C) {
-            return (EndIdx < C.getStartIdx() || StartIdx > C.getEndIdx());
-          })) {
-        // It doesn't overlap with anything, so we can outline it.
-        // Each sequence is over [StartIt, EndIt].
-        // Save the candidate and its location.
-
-        MachineBasicBlock::iterator StartIt = Mapper.InstrList[StartIdx];
-        MachineBasicBlock::iterator EndIt = Mapper.InstrList[EndIdx];
-        MachineBasicBlock *MBB = StartIt->getParent();
-
-        CandidatesForRepeatedSeq.emplace_back(StartIdx, StringLen, StartIt,
-                                              EndIt, MBB, FunctionList.size(),
-                                              Mapper.MBBFlagsMap[MBB]);
+      unsigned EndIdx = StartIdx + StringLen - 1;
+      auto FirstOverlap = find_if(
+          CandidatesForRepeatedSeq, [StartIdx, EndIdx](const Candidate &C) {
+            return EndIdx >= C.getStartIdx() && StartIdx <= C.getEndIdx();
+          });
+      if (FirstOverlap != CandidatesForRepeatedSeq.end()) {
+#ifndef NDEBUG
+        ++NumDiscarded;
+        LLVM_DEBUG(dbgs() << "    .. DISCARD candidate @ [" << StartIdx
+                          << ", " << EndIdx << "]; overlaps with candidate @ ["
+                          << FirstOverlap->getStartIdx() << ", "
+                          << FirstOverlap->getEndIdx() << "]\n");
+#endif
+        continue;
       }
+      // It doesn't overlap with anything, so we can outline it.
+      // Each sequence is over [StartIt, EndIt].
+      // Save the candidate and its location.
+#ifndef NDEBUG
+      ++NumKept;
+#endif
+      MachineBasicBlock::iterator StartIt = Mapper.InstrList[StartIdx];
+      MachineBasicBlock::iterator EndIt = Mapper.InstrList[EndIdx];
+      MachineBasicBlock *MBB = StartIt->getParent();
+      CandidatesForRepeatedSeq.emplace_back(StartIdx, StringLen, StartIt, EndIt,
+                                            MBB, FunctionList.size(),
+                                            Mapper.MBBFlagsMap[MBB]);
     }
+#ifndef NDEBUG
+    LLVM_DEBUG(dbgs() << "    Candidates discarded: " << NumDiscarded
+                      << "\n");
+    LLVM_DEBUG(dbgs() << "    Candidates kept: " << NumKept << "\n\n");
+#endif
 
     // We've found something we might want to outline.
     // Create an OutlinedFunction to store it and check if it'd be beneficial

llvm/test/CodeGen/AArch64/machine-outliner-overlap.mir

@@ -0,0 +1,84 @@
+# NOTE: Assertions have been autogenerated by utils/update_mir_test_checks.py UTC_ARGS: --include-generated-funcs
+# RUN: llc %s -mtriple aarch64 -debug-only=machine-outliner -run-pass=machine-outliner -o - 2>&1 | FileCheck %s
+# REQUIRES: asserts
+
+# CHECK: *** Discarding overlapping candidates ***
+# CHECK-NEXT:Searching for overlaps in all repeated sequences...
+# CHECK-DAG:  Sequence length: 7
+# CHECK-NEXT:    Candidates discarded: 0
+# CHECK-NEXT:    Candidates kept: 2
+# CHECK-DAG:  Sequence length: 8
+# CHECK-NEXT:    .. DISCARD candidate @ [5, 12]; overlaps with candidate @ [12, 19]
+# CHECK-NEXT:    Candidates discarded: 1
+# CHECK-NEXT:    Candidates kept: 1
+# CHECK-DAG:   Sequence length: 9
+# CHECK-NEXT:    .. DISCARD candidate @ [4, 12]; overlaps with candidate @ [11, 19]
+# CHECK-NEXT:    Candidates discarded: 1
+# CHECK-NEXT:    Candidates kept: 1
+# CHECK-DAG:   Sequence length: 10
+# CHECK-NEXT:    .. DISCARD candidate @ [3, 12]; overlaps with candidate @ [10, 19]
+# CHECK-NEXT:    Candidates discarded: 1
+# CHECK-NEXT:    Candidates kept: 1
+# CHECK-DAG:   Sequence length: 11
+# CHECK-NEXT:    .. DISCARD candidate @ [2, 12]; overlaps with candidate @ [9, 19]
+# CHECK-NEXT:    Candidates discarded: 1
+# CHECK-NEXT:    Candidates kept: 1
+# CHECK-DAG:   Sequence length: 12
+# CHECK-NEXT:    .. DISCARD candidate @ [1, 12]; overlaps with candidate @ [8, 19]
+# CHECK-NEXT:    Candidates discarded: 1
+# CHECK-NEXT:    Candidates kept: 1
+# CHECK-DAG:   Sequence length: 13
+# CHECK-NEXT:    .. DISCARD candidate @ [0, 12]; overlaps with candidate @ [7, 19]
+# CHECK-NEXT:    Candidates discarded: 1
+# CHECK-NEXT:    Candidates kept: 1
+
+...
+---
+name:           overlap
+tracksRegLiveness: true
+machineFunctionInfo:
+  hasRedZone:      false
+body:             |
+  bb.0:
+    liveins: $x0, $x9
+    ; CHECK-LABEL: name: overlap
+    ; CHECK: liveins: $x0, $x9
+    ; CHECK-NEXT: {{  $}}
+    ; CHECK-NEXT: $x9 = ADDXri $x9, 16, 0
+    ; CHECK-NEXT: $x9 = ADDXri $x9, 16, 0
+    ; CHECK-NEXT: $x9 = ADDXri $x9, 16, 0
+    ; CHECK-NEXT: $x9 = ADDXri $x9, 16, 0
+    ; CHECK-NEXT: $x9 = ADDXri $x9, 16, 0
+    ; CHECK-NEXT: $x9 = ADDXri $x9, 16, 0
+    ; CHECK-NEXT: BL @OUTLINED_FUNCTION_0, implicit-def $lr, implicit $sp, implicit-def $lr, implicit-def $x8, implicit-def $x9, implicit $sp, implicit $x0, implicit $x9
+    ; CHECK-NEXT: BL @OUTLINED_FUNCTION_0, implicit-def $lr, implicit $sp, implicit-def $lr, implicit-def $x8, implicit-def $x9, implicit $sp, implicit $x0, implicit $x9
+    ; CHECK-NEXT: RET undef $x9
+
+    ; fixme: outline!
+    $x9 = ADDXri $x9, 16, 0
+    $x9 = ADDXri $x9, 16, 0
+    $x9 = ADDXri $x9, 16, 0
+    $x9 = ADDXri $x9, 16, 0
+    $x9 = ADDXri $x9, 16, 0
+    $x9 = ADDXri $x9, 16, 0
+
+    $x8 = ADDXri $x0, 3, 0
+
+    ; outline
+    $x9 = ADDXri $x9, 16, 0
+    $x9 = ADDXri $x9, 16, 0
+    $x9 = ADDXri $x9, 16, 0
+    $x9 = ADDXri $x9, 16, 0
+    $x9 = ADDXri $x9, 16, 0
+    $x9 = ADDXri $x9, 16, 0
+
+    $x8 = ADDXri $x0, 3, 0
+
+    ; outline
+    $x9 = ADDXri $x9, 16, 0
+    $x9 = ADDXri $x9, 16, 0
+    $x9 = ADDXri $x9, 16, 0
+    $x9 = ADDXri $x9, 16, 0
+    $x9 = ADDXri $x9, 16, 0
+    $x9 = ADDXri $x9, 16, 0
+    RET undef $x9