Correctly modify the CFG in IfConverter, and then remove the

CorrectExtraCFGEdges function.

The latter was a workaround for "Various pieces of code" leaving bogus
extra CFG edges in place. Where by "various" it meant only
IfConverter::MergeBlocks, which failed to clear all of the successors
of dead blocks it emptied out. This wouldn't matter a whole lot,
except that the dead blocks remained listed as predecessors of
still-useful blocks, inhibiting optimizations.

This fix slightly changed two thumb tests, because the correct CFG
successors allowed for the "diamond" if-conversion pattern to be
detected, when it could only use "simple" before.

Additionally, the removal of a now-redundant call to analyzeBranch
(with AllowModify=true) in BranchFolder::OptimizeFunction caused a
later check for an empty block in BranchFolder::OptimizeBlock to
fail. Correct this by moving the call to analyzeBranch in
OptimizeBlock higher.

Differential Revision: https://reviews.llvm.org/D79527

1 files changed, 0 insertions, 62 deletions

diff --git a/llvm/lib/CodeGen/MachineBasicBlock.cpp b/llvm/lib/CodeGen/MachineBasicBlock.cpp
index 09e31af..9abd24e 100644
--- a/llvm/lib/CodeGen/MachineBasicBlock.cpp
+++ b/llvm/lib/CodeGen/MachineBasicBlock.cpp
@@ -1261,68 +1261,6 @@ void MachineBasicBlock::replacePhiUsesWith(MachineBasicBlock *Old,
     }
 }
 
-/// Various pieces of code can cause excess edges in the CFG to be inserted.  If
-/// we have proven that MBB can only branch to DestA and DestB, remove any other
-/// MBB successors from the CFG.  DestA and DestB can be null.
-///
-/// Besides DestA and DestB, retain other edges leading to LandingPads
-/// (currently there can be only one; we don't check or require that here).
-/// Note it is possible that DestA and/or DestB are LandingPads.
-bool MachineBasicBlock::CorrectExtraCFGEdges(MachineBasicBlock *DestA,
-                                             MachineBasicBlock *DestB,
-                                             bool IsCond) {
-  // The values of DestA and DestB frequently come from a call to the
-  // 'TargetInstrInfo::analyzeBranch' method. We take our meaning of the initial
-  // values from there.
-  //
-  // 1. If both DestA and DestB are null, then the block ends with no branches
-  //    (it falls through to its successor).
-  // 2. If DestA is set, DestB is null, and IsCond is false, then the block ends
-  //    with only an unconditional branch.
-  // 3. If DestA is set, DestB is null, and IsCond is true, then the block ends
-  //    with a conditional branch that falls through to a successor (DestB).
-  // 4. If DestA and DestB is set and IsCond is true, then the block ends with a
-  //    conditional branch followed by an unconditional branch. DestA is the
-  //    'true' destination and DestB is the 'false' destination.
-
-  bool Changed = false;
-
-  MachineBasicBlock *FallThru = getNextNode();
-
-  if (!DestA && !DestB) {
-    // Block falls through to successor.
-    DestA = FallThru;
-    DestB = FallThru;
-  } else if (DestA && !DestB) {
-    if (IsCond)
-      // Block ends in conditional jump that falls through to successor.
-      DestB = FallThru;
-  } else {
-    assert(DestA && DestB && IsCond &&
-           "CFG in a bad state. Cannot correct CFG edges");
-  }
-
-  // Remove superfluous edges. I.e., those which aren't destinations of this
-  // basic block, duplicate edges, or landing pads.
-  SmallPtrSet<const MachineBasicBlock*, 8> SeenMBBs;
-  MachineBasicBlock::succ_iterator SI = succ_begin();
-  while (SI != succ_end()) {
-    const MachineBasicBlock *MBB = *SI;
-    if (!SeenMBBs.insert(MBB).second ||
-        (MBB != DestA && MBB != DestB && !MBB->isEHPad())) {
-      // This is a superfluous edge, remove it.
-      SI = removeSuccessor(SI);
-      Changed = true;
-    } else {
-      ++SI;
-    }
-  }
-
-  if (Changed)
-    normalizeSuccProbs();
-  return Changed;
-}
-
 /// Find the next valid DebugLoc starting at MBBI, skipping any DBG_VALUE
 /// instructions.  Return UnknownLoc if there is none.
 DebugLoc