X-Git-Url: http://demsky.eecs.uci.edu/git/?a=blobdiff_plain;f=lib%2FCodeGen%2FMachineSink.cpp;h=7fb33c6e4cedf51301621c7593b88760a11a83da;hb=713f043c16220b746804f668a72f4e0344cbe4d1;hp=0f608d637c537a7fd4c1afab8e111c33ff441393;hpb=ae73dc1448d25b02cabc7c64c86c64371453dda8;p=oota-llvm.git

diff --git a/lib/CodeGen/MachineSink.cpp b/lib/CodeGen/MachineSink.cpp
index 0f608d637c5..7fb33c6e4ce 100644
--- a/lib/CodeGen/MachineSink.cpp
+++ b/lib/CodeGen/MachineSink.cpp
@@ -7,7 +7,12 @@
 //
 //===----------------------------------------------------------------------===//
 //
-// This pass 
+// This pass moves instructions into successor blocks, when possible, so that
+// they aren't executed on paths where their results aren't needed.
+//
+// This pass is not intended to be a replacement or a complete alternative
+// for an LLVM-IR-level sinking pass. It is only designed to sink simple
+// constructs that are not exposed before lowering and instruction selection.
 //
 //===----------------------------------------------------------------------===//
 
@@ -18,10 +23,10 @@
 #include "llvm/Target/TargetRegisterInfo.h"
 #include "llvm/Target/TargetInstrInfo.h"
 #include "llvm/Target/TargetMachine.h"
-#include "llvm/ADT/SmallVector.h"
 #include "llvm/ADT/Statistic.h"
 #include "llvm/Support/Compiler.h"
 #include "llvm/Support/Debug.h"
+#include "llvm/Support/raw_ostream.h"
 using namespace llvm;
 
 STATISTIC(NumSunk, "Number of machine instructions sunk");
@@ -32,7 +37,7 @@ namespace {
     const TargetInstrInfo *TII;
     MachineFunction       *CurMF; // Current MachineFunction
     MachineRegisterInfo  *RegInfo; // Machine register information
-    MachineDominatorTree *DT;   // Machine dominator tree for the current Loop
+    MachineDominatorTree *DT;   // Machine dominator tree
 
   public:
     static char ID; // Pass identification
@@ -41,6 +46,7 @@ namespace {
     virtual bool runOnMachineFunction(MachineFunction &MF);
     
     virtual void getAnalysisUsage(AnalysisUsage &AU) const {
+      AU.setPreservesCFG();
       MachineFunctionPass::getAnalysisUsage(AU);
       AU.addRequired<MachineDominatorTree>();
       AU.addPreserved<MachineDominatorTree>();
@@ -86,7 +92,7 @@ bool MachineSinking::AllUsesDominatedByBlock(unsigned Reg,
 
 
 bool MachineSinking::runOnMachineFunction(MachineFunction &MF) {
-  DOUT << "******** Machine Sinking ********\n";
+  DEBUG(errs() << "******** Machine Sinking ********\n");
   
   CurMF = &MF;
   TM = &CurMF->getTarget();
@@ -112,20 +118,29 @@ bool MachineSinking::runOnMachineFunction(MachineFunction &MF) {
 }
 
 bool MachineSinking::ProcessBlock(MachineBasicBlock &MBB) {
-  bool MadeChange = false;
-  
   // Can't sink anything out of a block that has less than two successors.
-  if (MBB.succ_size() <= 1) return false;
-  
+  if (MBB.succ_size() <= 1 || MBB.empty()) return false;
+
+  bool MadeChange = false;
+
   // Walk the basic block bottom-up.  Remember if we saw a store.
-  bool SawStore = false;
-  for (MachineBasicBlock::iterator I = MBB.end(); I != MBB.begin(); ){
-    MachineBasicBlock::iterator LastIt = I;
-    if (SinkInstruction(--I, SawStore)) {
-      I = LastIt;
-      ++NumSunk;
-    }
-  }
+  MachineBasicBlock::iterator I = MBB.end();
+  --I;
+  bool ProcessedBegin, SawStore = false;
+  do {
+    MachineInstr *MI = I;  // The instruction to sink.
+    
+    // Predecrement I (if it's not begin) so that it isn't invalidated by
+    // sinking.
+    ProcessedBegin = I == MBB.begin();
+    if (!ProcessedBegin)
+      --I;
+    
+    if (SinkInstruction(MI, SawStore))
+      ++NumSunk, MadeChange = true;
+    
+    // If we just processed the first instruction in the block, we're done.
+  } while (!ProcessedBegin);
   
   return MadeChange;
 }
@@ -143,7 +158,7 @@ bool MachineSinking::SinkInstruction(MachineInstr *MI, bool &SawStore) {
   // also sink them down before their first use in the block.  This xform has to
   // be careful not to *increase* register pressure though, e.g. sinking
   // "x = y + z" down if it kills y and z would increase the live ranges of y
-  // and z only the shrink the live range of x.
+  // and z and only shrink the live range of x.
   
   // Loop over all the operands of the specified instruction.  If there is
   // anything we can't handle, bail out.
@@ -168,6 +183,10 @@ bool MachineSinking::SinkInstruction(MachineInstr *MI, bool &SawStore) {
     } else {
       // Virtual register uses are always safe to sink.
       if (MO.isUse()) continue;
+
+      // If it's not safe to move defs of the register class, then abort.
+      if (!TII->isSafeToMoveRegClassDefs(RegInfo->getRegClass(Reg)))
+        return false;
       
       // FIXME: This picks a successor to sink into based on having one
       // successor that dominates all the uses.  However, there are cases where
@@ -209,16 +228,26 @@ bool MachineSinking::SinkInstruction(MachineInstr *MI, bool &SawStore) {
   // If there are no outputs, it must have side-effects.
   if (SuccToSinkTo == 0)
     return false;
+
+  // It's not safe to sink instructions to EH landing pad. Control flow into
+  // landing pad is implicitly defined.
+  if (SuccToSinkTo->isLandingPad())
+    return false;
+  
+  // If is not possible to sink an instruction into its own block.  This can
+  // happen with loops.
+  if (MI->getParent() == SuccToSinkTo)
+    return false;
   
-  DEBUG(cerr << "Sink instr " << *MI);
-  DEBUG(cerr << "to block " << *SuccToSinkTo);
+  DEBUG(errs() << "Sink instr " << *MI);
+  DEBUG(errs() << "to block " << *SuccToSinkTo);
   
   // If the block has multiple predecessors, this would introduce computation on
   // a path that it doesn't already exist.  We could split the critical edge,
   // but for now we just punt.
   // FIXME: Split critical edges if not backedges.
   if (SuccToSinkTo->pred_size() > 1) {
-    DEBUG(cerr << " *** PUNTING: Critical edge found\n");
+    DEBUG(errs() << " *** PUNTING: Critical edge found\n");
     return false;
   }