Allow ARM if-converter to be run after post allocation scheduling.

- This fixed a number of bugs in if-converter, tail merging, and post-allocation
  scheduler. If-converter now runs branch folding / tail merging first to
  maximize if-conversion opportunities.
- Also changed the t2IT instruction slightly. It now defines the ITSTATE
  register which is read by instructions in the IT block.
- Added Thumb2 specific hazard recognizer to ensure the scheduler doesn't
  change the instruction ordering in the IT block (since IT mask has been
  finalized). It also ensures no other instructions can be scheduled between
  instructions in the IT block.

This is not yet enabled.

llvm-svn: 106344

1 files changed, 58 insertions, 1 deletions

diff --git a/llvm/lib/Target/ARM/Thumb2InstrInfo.cpp b/llvm/lib/Target/ARM/Thumb2InstrInfo.cpp
index f78111f7b92..866ffb19884 100644
--- a/llvm/lib/Target/ARM/Thumb2InstrInfo.cpp
+++ b/llvm/lib/Target/ARM/Thumb2InstrInfo.cpp
@@ -17,12 +17,13 @@
 #include "ARMAddressingModes.h"
 #include "ARMGenInstrInfo.inc"
 #include "ARMMachineFunctionInfo.h"
+#include "Thumb2HazardRecognizer.h"
+#include "Thumb2InstrInfo.h"
 #include "llvm/CodeGen/MachineFrameInfo.h"
 #include "llvm/CodeGen/MachineInstrBuilder.h"
 #include "llvm/CodeGen/MachineMemOperand.h"
 #include "llvm/CodeGen/PseudoSourceValue.h"
 #include "llvm/ADT/SmallVector.h"
-#include "Thumb2InstrInfo.h"
 
 using namespace llvm;
 
@@ -35,6 +36,57 @@ unsigned Thumb2InstrInfo::getUnindexedOpcode(unsigned Opc) const {
   return 0;
 }
 
+void
+Thumb2InstrInfo::ReplaceTailWithBranchTo(MachineBasicBlock::iterator Tail,
+                                         MachineBasicBlock *NewDest) const {
+  MachineBasicBlock *MBB = Tail->getParent();
+  ARMFunctionInfo *AFI = MBB->getParent()->getInfo<ARMFunctionInfo>();
+  if (!AFI->hasITBlocks()) {
+    TargetInstrInfoImpl::ReplaceTailWithBranchTo(Tail, NewDest);
+    return;
+  }
+
+  // If the first instruction of Tail is predicated, we may have to update
+  // the IT instruction.
+  unsigned PredReg = 0;
+  ARMCC::CondCodes CC = llvm::getInstrPredicate(Tail, PredReg);
+  MachineBasicBlock::iterator MBBI = Tail;
+  if (CC != ARMCC::AL)
+    // Expecting at least the t2IT instruction before it.
+    --MBBI;
+
+  // Actually replace the tail.
+  TargetInstrInfoImpl::ReplaceTailWithBranchTo(Tail, NewDest);
+
+  // Fix up IT.
+  if (CC != ARMCC::AL) {
+    MachineBasicBlock::iterator E = MBB->begin();
+    unsigned Count = 4; // At most 4 instructions in an IT block.
+    while (Count && MBBI != E) {
+      if (MBBI->isDebugValue()) {
+        --MBBI;
+        continue;
+      }
+      if (MBBI->getOpcode() == ARM::t2IT) {
+        unsigned Mask = MBBI->getOperand(1).getImm();
+        if (Count == 4)
+          MBBI->eraseFromParent();
+        else {
+          unsigned MaskOn = 1 << Count;
+          unsigned MaskOff = ~(MaskOn - 1);
+          MBBI->getOperand(1).setImm((Mask & MaskOff) | MaskOn);
+        }
+        return;
+      }
+      --MBBI;
+      --Count;
+    }
+
+    // Ctrl flow can reach here if branch folding is run before IT block
+    // formation pass.
+  }
+}
+
 bool
 Thumb2InstrInfo::copyRegToReg(MachineBasicBlock &MBB,
                               MachineBasicBlock::iterator I,
@@ -116,6 +168,11 @@ loadRegFromStackSlot(MachineBasicBlock &MBB, MachineBasicBlock::iterator I,
   ARMBaseInstrInfo::loadRegFromStackSlot(MBB, I, DestReg, FI, RC, TRI);
 }
 
+ScheduleHazardRecognizer *Thumb2InstrInfo::
+CreateTargetPostRAHazardRecognizer(const InstrItineraryData &II) const {
+  return (ScheduleHazardRecognizer *)new Thumb2HazardRecognizer(II);
+}
+
 void llvm::emitT2RegPlusImmediate(MachineBasicBlock &MBB,
                                MachineBasicBlock::iterator &MBBI, DebugLoc dl,
                                unsigned DestReg, unsigned BaseReg, int NumBytes,