From: Bill Wendling <isanbard@gmail.com>
Date: Fri, 11 Dec 2009 21:47:36 +0000 (+0000)
Subject: Don't try to move a MBB into the fall-through position if it's a landing pad or
X-Git-Url: http://plrg.eecs.uci.edu/git/?a=commitdiff_plain;h=c42a0b75a41144be86d40872b57850ab578969ea;p=oota-llvm.git

Don't try to move a MBB into the fall-through position if it's a landing pad or
branches only to a landing pad. Without this check, the compiler would go into
an infinite loop because the branch to a landing pad is an "abnormal" edge which
wasn't being taken into account.

This is the meat of that fix:

  if (!PrevBB.canFallThrough() && !MBB->BranchesToLandingPad(MBB)) {

The other stuff is simplification of the "branches to a landing pad" code.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@91161 91177308-0d34-0410-b5e6-96231b3b80d8
---

diff --git a/lib/CodeGen/BranchFolding.cpp b/lib/CodeGen/BranchFolding.cpp
index 3887e6d44e4..7ac8bda7a35 100644
--- a/lib/CodeGen/BranchFolding.cpp
+++ b/lib/CodeGen/BranchFolding.cpp
@@ -1205,11 +1205,11 @@ ReoptimizeBlock:
     }
   }
 
-  // If the prior block doesn't fall through into this block, and if this
-  // block doesn't fall through into some other block, see if we can find a
-  // place to move this block where a fall-through will happen.
-  if (!PrevBB.canFallThrough()) {
-
+  // If the prior block doesn't fall through into this block and if this block
+  // doesn't fall through into some other block and it's not branching only to a
+  // landing pad, then see if we can find a place to move this block where a
+  // fall-through will happen.
+  if (!PrevBB.canFallThrough() && !MBB->BranchesToLandingPad(MBB)) {
     // Now we know that there was no fall-through into this block, check to
     // see if it has a fall-through into its successor.
     bool CurFallsThru = MBB->canFallThrough();
@@ -1221,28 +1221,32 @@ ReoptimizeBlock:
            E = MBB->pred_end(); PI != E; ++PI) {
         // Analyze the branch at the end of the pred.
         MachineBasicBlock *PredBB = *PI;
-        MachineFunction::iterator PredFallthrough = PredBB; ++PredFallthrough;
+        MachineFunction::iterator PredNextBB = PredBB; ++PredNextBB;
         MachineBasicBlock *PredTBB, *PredFBB;
         SmallVector<MachineOperand, 4> PredCond;
-        if (PredBB != MBB && !PredBB->canFallThrough() &&
-            !TII->AnalyzeBranch(*PredBB, PredTBB, PredFBB, PredCond, true)
+        if (PredBB != MBB && !PredBB->canFallThrough()
+            && !TII->AnalyzeBranch(*PredBB, PredTBB, PredFBB, PredCond, true)
             && (!CurFallsThru || !CurTBB || !CurFBB)
             && (!CurFallsThru || MBB->getNumber() >= PredBB->getNumber())) {
-          // If the current block doesn't fall through, just move it.
-          // If the current block can fall through and does not end with a
-          // conditional branch, we need to append an unconditional jump to
-          // the (current) next block.  To avoid a possible compile-time
-          // infinite loop, move blocks only backward in this case.
-          // Also, if there are already 2 branches here, we cannot add a third;
-          // this means we have the case
-          // Bcc next
-          // B elsewhere
-          // next:
+          // If the current block doesn't fall through, just move it.  If the
+          // current block can fall through and does not end with a conditional
+          // branch, we need to append an unconditional jump to the (current)
+          // next block.  To avoid a possible compile-time infinite loop, move
+          // blocks only backward in this case.
+          // 
+          // Also, if there are already 2 branches here, we cannot add a third.
+          // I.e. we have the case:
+          // 
+          //     Bcc next
+          //     B elsewhere
+          //   next:
           if (CurFallsThru) {
-            MachineBasicBlock *NextBB = llvm::next(MachineFunction::iterator(MBB));
+            MachineBasicBlock *NextBB =
+              llvm::next(MachineFunction::iterator(MBB));
             CurCond.clear();
             TII->InsertBranch(*MBB, NextBB, 0, CurCond);
           }
+
           MBB->moveAfter(PredBB);
           MadeChange = true;
           goto ReoptimizeBlock;
diff --git a/lib/CodeGen/MachineBasicBlock.cpp b/lib/CodeGen/MachineBasicBlock.cpp
index 0097dd16105..80b4b0ffd8d 100644
--- a/lib/CodeGen/MachineBasicBlock.cpp
+++ b/lib/CodeGen/MachineBasicBlock.cpp
@@ -457,16 +457,9 @@ MachineBasicBlock::BranchesToLandingPad(const MachineBasicBlock *MBB) const {
   SmallSet<const MachineBasicBlock*, 32> Visited;
   const MachineBasicBlock *CurMBB = MBB;
 
-  while (!Visited.count(CurMBB) && !CurMBB->isLandingPad()) {
-    if (CurMBB->size() != 1 || CurMBB->succ_empty() || CurMBB->succ_size() != 1)
-      break;
-
-    const TargetInstrInfo *TII =
-      CurMBB->getParent()->getTarget().getInstrInfo();
-    if (!TII->isUnpredicatedTerminator(CurMBB->begin()))
-      break;
-
-    Visited.insert(CurMBB);
+  while (!CurMBB->isLandingPad()) {
+    if (CurMBB->succ_size() != 1) break;
+    if (!Visited.insert(CurMBB)) break;
     CurMBB = *CurMBB->succ_begin();
   }