X-Git-Url: http://demsky.eecs.uci.edu/git/?a=blobdiff_plain;f=lib%2FCodeGen%2FCodePlacementOpt.cpp;h=270c337ef67ecb7265b6a298b1318bc61c010071;hb=596f447467b35d7513c997cd9098026938676461;hp=05a57d45343f85f7c55a2b9c9b579652feecfd37;hpb=f451cb870efcf9e0302d25ed05f4cac6bb494e42;p=oota-llvm.git

diff --git a/lib/CodeGen/CodePlacementOpt.cpp b/lib/CodeGen/CodePlacementOpt.cpp
index 05a57d45343..270c337ef67 100644
--- a/lib/CodeGen/CodePlacementOpt.cpp
+++ b/lib/CodeGen/CodePlacementOpt.cpp
@@ -7,8 +7,8 @@
 //
 //===----------------------------------------------------------------------===//
 //
-// This file implements the pass that optimize code placement and align loop
-// headers to target specific alignment boundary.
+// This file implements the pass that optimizes code placement and aligns loop
+// headers to target-specific alignment boundaries.
 //
 //===----------------------------------------------------------------------===//
 
@@ -36,11 +36,11 @@ namespace {
 
   public:
     static char ID;
-    CodePlacementOpt() : MachineFunctionPass(&ID) {}
+    CodePlacementOpt() : MachineFunctionPass(ID) {}
 
     virtual bool runOnMachineFunction(MachineFunction &MF);
     virtual const char *getPassName() const {
-      return "Code Placement Optimizater";
+      return "Code Placement Optimizer";
     }
 
     virtual void getAnalysisUsage(AnalysisUsage &AU) const {
@@ -102,22 +102,23 @@ bool CodePlacementOpt::HasAnalyzableTerminator(MachineBasicBlock *MBB) {
   // Conservatively ignore EH landing pads.
   if (MBB->isLandingPad()) return false;
 
-  // Ignore blocks which look like they might have EH-related control flow.
-  // At the time of this writing, there are blocks which AnalyzeBranch
-  // thinks end in single uncoditional branches, yet which have two CFG
-  // successors. Code in this file is not prepared to reason about such things.
-  if (!MBB->empty() && MBB->back().isEHLabel())
-    return false;
-
   // Aggressively handle return blocks and similar constructs.
   if (MBB->succ_empty()) return true;
 
   // Ask the target's AnalyzeBranch if it can handle this block.
   MachineBasicBlock *TBB = 0, *FBB = 0;
   SmallVector<MachineOperand, 4> Cond;
-  // Make the terminator is understood.
+  // Make sure the terminator is understood.
   if (TII->AnalyzeBranch(*MBB, TBB, FBB, Cond))
     return false;
+   // Ignore blocks which look like they might have EH-related control flow.
+   // AnalyzeBranch thinks it knows how to analyze such things, but it doesn't
+   // recognize the possibility of a control transfer through an unwind.
+   // Such blocks contain EH_LABEL instructions, however they may be in the
+   // middle of the block. Instead of searching for them, just check to see
+   // if the CFG disagrees with AnalyzeBranch.
+  if (1u + !Cond.empty() != MBB->succ_size())
+    return false;
   // Make sure we have the option of reversing the condition.
   if (!Cond.empty() && TII->ReverseBranchCondition(Cond))
     return false;
@@ -177,6 +178,8 @@ bool CodePlacementOpt::EliminateUnconditionalJumpsToTop(MachineFunction &MF,
         continue;
 
       // Move the block.
+      DEBUG(dbgs() << "CGP: Moving blocks starting at BB#" << Pred->getNumber()
+                   << " to top of loop.\n");
       Changed = true;
 
       // Move it and all the blocks that can reach it via fallthrough edges
@@ -251,7 +254,7 @@ bool CodePlacementOpt::MoveDiscontiguousLoopBlocks(MachineFunction &MF,
 
   // Determine a position to move orphaned loop blocks to. If TopMBB is not
   // entered via fallthrough and BotMBB is exited via fallthrough, prepend them
-  // to the top of the loop to avoid loosing that fallthrough. Otherwise append
+  // to the top of the loop to avoid losing that fallthrough. Otherwise append
   // them to the bottom, even if it previously had a fallthrough, on the theory
   // that it's worth an extra branch to keep the loop contiguous.
   MachineFunction::iterator InsertPt =
@@ -296,6 +299,8 @@ bool CodePlacementOpt::MoveDiscontiguousLoopBlocks(MachineFunction &MF,
         continue;
 
       // Move the block.
+      DEBUG(dbgs() << "CGP: Moving blocks starting at BB#" << BB->getNumber()
+                   << " to be contiguous with loop.\n");
       Changed = true;
 
       // Process this block and all loop blocks contiguous with it, to keep