Revert "[CFIFixup] Factor logic into helpers and use range-based loops (NFC) (#125137)"

This reverts commit f14f197, which
breaks a number of build bots:
- https://lab.llvm.org/buildbot/#/builders/163/builds/12726
- https://lab.llvm.org/buildbot/#/builders/144/builds/17106
- https://lab.llvm.org/buildbot/#/builders/123/builds/12855
- https://lab.llvm.org/buildbot/#/builders/133/builds/10660
- https://lab.llvm.org/buildbot/#/builders/88/builds/7482
- https://lab.llvm.org/buildbot/#/builders/180/builds/12313
- https://lab.llvm.org/buildbot/#/builders/160/builds/12316

Author: dhoekwater

llvm/lib/CodeGen/CFIFixup.cpp

@@ -70,7 +70,6 @@
 #include "llvm/ADT/DenseMap.h"
 #include "llvm/ADT/PostOrderIterator.h"
 #include "llvm/ADT/STLExtras.h"
-#include "llvm/ADT/SmallVector.h"
 #include "llvm/ADT/iterator_range.h"
 #include "llvm/CodeGen/MachineBasicBlock.h"
 #include "llvm/CodeGen/MachineFunction.h"
@@ -123,57 +122,6 @@ findPrologueEnd(MachineFunction &MF, MachineBasicBlock::iterator &PrologueEnd) {
   return nullptr;
 }
 
-// Represents a basic block's relationship to the call frame. This metadata
-// reflects what the state *should* be, which may differ from the actual state
-// after final machine basic block layout.
-struct BlockFlags {
-  bool Reachable : 1;
-  bool StrongNoFrameOnEntry : 1;
-  bool HasFrameOnEntry : 1;
-  bool HasFrameOnExit : 1;
-};
-
-// Computes the frame information for each block in the function. Frame info
-// for a block is inferred from its predecessors.
-static SmallVector<BlockFlags>
-computeBlockInfo(const MachineFunction &MF,
-                 const MachineBasicBlock *PrologueBlock) {
-  SmallVector<BlockFlags, 32> BlockInfo(MF.getNumBlockIDs(),
-                                        {false, false, false, false});
-  BlockInfo[0].Reachable = true;
-  BlockInfo[0].StrongNoFrameOnEntry = true;
-
-  // Compute the presence/absence of frame at each basic block.
-  ReversePostOrderTraversal<const MachineBasicBlock *> RPOT(&*MF.begin());
-  for (const MachineBasicBlock *MBB : RPOT) {
-    BlockFlags &Info = BlockInfo[MBB->getNumber()];
-
-    // Set to true if the current block contains the prologue or the epilogue,
-    // respectively.
-    bool HasPrologue = MBB == PrologueBlock;
-    bool HasEpilogue = false;
-
-    if (Info.HasFrameOnEntry || HasPrologue)
-      HasEpilogue = containsEpilogue(*MBB);
-
-    // If the function has a call frame at the entry of the current block or the
-    // current block contains the prologue, then the function has a call frame
-    // at the exit of the block, unless the block contains the epilogue.
-    Info.HasFrameOnExit = (Info.HasFrameOnEntry || HasPrologue) && !HasEpilogue;
-
-    // Set the successors' state on entry.
-    for (MachineBasicBlock *Succ : MBB->successors()) {
-      BlockFlags &SuccInfo = BlockInfo[Succ->getNumber()];
-      SuccInfo.Reachable = true;
-      SuccInfo.StrongNoFrameOnEntry |=
-          Info.StrongNoFrameOnEntry && !HasPrologue;
-      SuccInfo.HasFrameOnEntry = Info.HasFrameOnExit;
-    }
-  }
-
-  return BlockInfo;
-}
-
 // Represents the point within a basic block where we can insert an instruction.
 // Note that we need the MachineBasicBlock* as well as the iterator since the
 // iterator can point to the end of the block. Instructions are inserted
@@ -233,69 +181,13 @@ static InsertionPoint cloneCfiPrologue(const InsertionPoint &PrologueEnd,
   return DstInsertPt;
 }
 
-// Fixes up the CFI instructions in a basic block to be consistent with the
-// intended frame state, adding or removing CFI instructions as necessary.
-// Returns true if a change was made and false otherwise.
-static bool
-fixupBlock(MachineBasicBlock &CurrBB, const SmallVector<BlockFlags> &BlockInfo,
-           SmallDenseMap<MBBSectionID, InsertionPoint> &InsertionPts,
-           const InsertionPoint &Prologue) {
-  const MachineFunction &MF = *CurrBB.getParent();
-  const TargetFrameLowering &TFL = *MF.getSubtarget().getFrameLowering();
-  const BlockFlags &Info = BlockInfo[CurrBB.getNumber()];
-
-  if (!Info.Reachable)
-    return false;
-
-  // If the previous block and the current block are in the same section,
-  // the frame info will propagate from the previous block to the current one.
-  const BlockFlags &PrevInfo =
-      BlockInfo[std::prev(CurrBB.getIterator())->getNumber()];
-  bool HasFrame = PrevInfo.HasFrameOnExit && !CurrBB.isBeginSection();
-  bool NeedsFrame = Info.HasFrameOnEntry && !Info.StrongNoFrameOnEntry;
-
-#ifndef NDEBUG
-  if (!Info.StrongNoFrameOnEntry) {
-    for (auto *Pred : CurrBB.predecessors()) {
-      const BlockFlags &PredInfo = BlockInfo[Pred->getNumber()];
-      assert((!PredInfo.Reachable ||
-              Info.HasFrameOnEntry == PredInfo.HasFrameOnExit) &&
-             "Inconsistent call frame state");
-    }
-  }
-#endif
-
-  if (HasFrame == NeedsFrame)
-    return false;
-
-  if (!NeedsFrame) {
-    // Reset to the state upon function entry.
-    TFL.resetCFIToInitialState(CurrBB);
-    return true;
-  }
-
-  // Reset to the "after prologue" state.
-  InsertionPoint &InsertPt = InsertionPts[CurrBB.getSectionID()];
-  if (InsertPt.MBB == nullptr) {
-    // CurBB is the first block in its section, so there is no "after
-    // prologue" state. Clone the CFI instructions from the prologue block
-    // to create it.
-    InsertPt = cloneCfiPrologue(Prologue, {&CurrBB, CurrBB.begin()});
-  } else {
-    // There's an earlier block known to have a stack frame. Insert a
-    // `.cfi_remember_state` instruction into that block and a
-    // `.cfi_restore_state` instruction at the beginning of the current
-    // block.
-    InsertPt = insertRememberRestorePair(InsertPt, {&CurrBB, CurrBB.begin()});
-  }
-  return true;
-}
-
 bool CFIFixup::runOnMachineFunction(MachineFunction &MF) {
-  if (!MF.getSubtarget().getFrameLowering()->enableCFIFixup(MF))
+  const TargetFrameLowering &TFL = *MF.getSubtarget().getFrameLowering();
+  if (!TFL.enableCFIFixup(MF))
     return false;
 
-  if (MF.getNumBlockIDs() < 2)
+  const unsigned NumBlocks = MF.getNumBlockIDs();
+  if (NumBlocks < 2)
     return false;
 
   // Find the prologue and the point where we can issue the first
@@ -305,7 +197,44 @@ bool CFIFixup::runOnMachineFunction(MachineFunction &MF) {
   if (PrologueBlock == nullptr)
     return false;
 
-  SmallVector<BlockFlags> BlockInfo = computeBlockInfo(MF, PrologueBlock);
+  struct BlockFlags {
+    bool Reachable : 1;
+    bool StrongNoFrameOnEntry : 1;
+    bool HasFrameOnEntry : 1;
+    bool HasFrameOnExit : 1;
+  };
+  SmallVector<BlockFlags, 32> BlockInfo(NumBlocks,
+                                        {false, false, false, false});
+  BlockInfo[0].Reachable = true;
+  BlockInfo[0].StrongNoFrameOnEntry = true;
+
+  // Compute the presence/absence of frame at each basic block.
+  ReversePostOrderTraversal<MachineBasicBlock *> RPOT(&*MF.begin());
+  for (MachineBasicBlock *MBB : RPOT) {
+    BlockFlags &Info = BlockInfo[MBB->getNumber()];
+
+    // Set to true if the current block contains the prologue or the epilogue,
+    // respectively.
+    bool HasPrologue = MBB == PrologueBlock;
+    bool HasEpilogue = false;
+
+    if (Info.HasFrameOnEntry || HasPrologue)
+      HasEpilogue = containsEpilogue(*MBB);
+
+    // If the function has a call frame at the entry of the current block or the
+    // current block contains the prologue, then the function has a call frame
+    // at the exit of the block, unless the block contains the epilogue.
+    Info.HasFrameOnExit = (Info.HasFrameOnEntry || HasPrologue) && !HasEpilogue;
+
+    // Set the successors' state on entry.
+    for (MachineBasicBlock *Succ : MBB->successors()) {
+      BlockFlags &SuccInfo = BlockInfo[Succ->getNumber()];
+      SuccInfo.Reachable = true;
+      SuccInfo.StrongNoFrameOnEntry |=
+          Info.StrongNoFrameOnEntry && !HasPrologue;
+      SuccInfo.HasFrameOnEntry = Info.HasFrameOnExit;
+    }
+  }
 
   // Walk the blocks of the function in "physical" order.
   // Every block inherits the frame state (as recorded in the unwind tables)
@@ -324,10 +253,57 @@ bool CFIFixup::runOnMachineFunction(MachineFunction &MF) {
   // No point starting before the prologue block.
   // TODO: the unwind tables will still be incorrect if an epilogue physically
   // preceeds the prologue.
-  for (MachineBasicBlock &MBB :
-       make_range(std::next(PrologueBlock->getIterator()), MF.end())) {
-    Change |=
-        fixupBlock(MBB, BlockInfo, InsertionPts, {PrologueBlock, PrologueEnd});
+  MachineFunction::iterator CurrBB = std::next(PrologueBlock->getIterator());
+  bool HasFrame = BlockInfo[PrologueBlock->getNumber()].HasFrameOnExit;
+  while (CurrBB != MF.end()) {
+    const BlockFlags &Info = BlockInfo[CurrBB->getNumber()];
+    if (!Info.Reachable) {
+      ++CurrBB;
+      continue;
+    }
+
+#ifndef NDEBUG
+    if (!Info.StrongNoFrameOnEntry) {
+      for (auto *Pred : CurrBB->predecessors()) {
+        BlockFlags &PredInfo = BlockInfo[Pred->getNumber()];
+        assert((!PredInfo.Reachable ||
+                Info.HasFrameOnEntry == PredInfo.HasFrameOnExit) &&
+               "Inconsistent call frame state");
+      }
+    }
+#endif
+
+    // If the block is the first block in its section, then it doesn't have a
+    // frame on entry.
+    HasFrame &= !CurrBB->isBeginSection();
+    if (!Info.StrongNoFrameOnEntry && Info.HasFrameOnEntry && !HasFrame) {
+      // Reset to the "after prologue" state.
+
+      InsertionPoint &InsertPt = InsertionPts[CurrBB->getSectionID()];
+      if (InsertPt.MBB == nullptr) {
+        // CurBB is the first block in its section, so there is no "after
+        // prologue" state. Clone the CFI instructions from the prologue block
+        // to create it.
+        InsertPt = cloneCfiPrologue({PrologueBlock, PrologueEnd},
+                                    {&*CurrBB, CurrBB->begin()});
+      } else {
+        // There's an earlier block known to have a stack frame. Insert a
+        // `.cfi_remember_state` instruction into that block and a
+        // `.cfi_restore_state` instruction at the beginning of the current
+        // block.
+        InsertPt =
+            insertRememberRestorePair(InsertPt, {&*CurrBB, CurrBB->begin()});
+      }
+      Change = true;
+    } else if ((Info.StrongNoFrameOnEntry || !Info.HasFrameOnEntry) &&
+               HasFrame) {
+      // Reset to the state upon function entry.
+      TFL.resetCFIToInitialState(*CurrBB);
+      Change = true;
+    }
+
+    HasFrame = Info.HasFrameOnExit;
+    ++CurrBB;
   }
 
   return Change;