From f3a1fce8ae411ea7135bc48495e09538d492929e Mon Sep 17 00:00:00 2001
From: Evan Cheng <evan.cheng@apple.com>
Date: Sat, 25 Jul 2009 00:33:29 +0000
Subject: Change Thumb2 jumptable codegen to one that uses two level jumps:

Before:
      adr r12, #LJTI3_0_0
      ldr pc, [r12, +r0, lsl #2]
LJTI3_0_0:
      .long    LBB3_24
      .long    LBB3_30
      .long    LBB3_31
      .long    LBB3_32

After:
      adr r12, #LJTI3_0_0
      add pc, r12, +r0, lsl #2
LJTI3_0_0:
      b.w    LBB3_24
      b.w    LBB3_30
      b.w    LBB3_31
      b.w    LBB3_32

This has several advantages.
1. This will make it easier to optimize this to a TBB / TBH instruction +
   (smaller) table.
2. This eliminate the need for ugly asm printer hack to force the address
   into thumb addresses (bit 0 is one).
3. Same codegen for pic and non-pic.
4. This eliminate the need to align the table so constantpool island pass
   won't have to over-estimate the size.

Based on my calculation, the later is probably slightly faster as well since
ldr pc with shifter address is very slow. That is, it should be a win as long
as the HW implementation can do a reasonable job of branch predict the second
branch.

llvm-svn: 77024
---
 llvm/lib/Target/ARM/AsmPrinter/ARMAsmPrinter.cpp | 47 ++++++++++++++----------
 1 file changed, 27 insertions(+), 20 deletions(-)

(limited to 'llvm/lib/Target/ARM/AsmPrinter/ARMAsmPrinter.cpp')

diff --git a/llvm/lib/Target/ARM/AsmPrinter/ARMAsmPrinter.cpp b/llvm/lib/Target/ARM/AsmPrinter/ARMAsmPrinter.cpp
index 4d21d5cfd90..cffbecd764b 100644
--- a/llvm/lib/Target/ARM/AsmPrinter/ARMAsmPrinter.cpp
+++ b/llvm/lib/Target/ARM/AsmPrinter/ARMAsmPrinter.cpp
@@ -160,6 +160,7 @@ namespace {
     void printCPInstOperand(const MachineInstr *MI, int OpNum,
                             const char *Modifier);
     void printJTBlockOperand(const MachineInstr *MI, int OpNum);
+    void printJT2BlockOperand(const MachineInstr *MI, int OpNum);
 
     virtual bool PrintAsmOperand(const MachineInstr *MI, unsigned OpNum,
                                  unsigned AsmVariant, const char *ExtraCode);
@@ -907,6 +908,8 @@ void ARMAsmPrinter::printCPInstOperand(const MachineInstr *MI, int OpNum,
 }
 
 void ARMAsmPrinter::printJTBlockOperand(const MachineInstr *MI, int OpNum) {
+  assert(!Subtarget->isThumb2() && "Thumb2 should use double-jump jumptables!");
+
   const MachineOperand &MO1 = MI->getOperand(OpNum);
   const MachineOperand &MO2 = MI->getOperand(OpNum+1); // Unique Id
   unsigned JTI = MO1.getIndex();
@@ -922,23 +925,13 @@ void ARMAsmPrinter::printJTBlockOperand(const MachineInstr *MI, int OpNum) {
   const std::vector<MachineJumpTableEntry> &JT = MJTI->getJumpTables();
   const std::vector<MachineBasicBlock*> &JTBBs = JT[JTI].MBBs;
   bool UseSet= TAI->getSetDirective() && TM.getRelocationModel() == Reloc::PIC_;
-  bool NeedBit0 = Subtarget->isTargetDarwin() && Subtarget->isThumb2();
   SmallPtrSet<MachineBasicBlock*, 8> JTSets;
   for (unsigned i = 0, e = JTBBs.size(); i != e; ++i) {
     MachineBasicBlock *MBB = JTBBs[i];
-    if (UseSet && JTSets.insert(MBB)) {
-      // FIXME: Temporary workaround for an assembler bug. The assembler isn't
-      // setting the bit zero to 1 even though it is a thumb address.
-      if (NeedBit0) {
-        O << TAI->getSetDirective() << ' ' << TAI->getPrivateGlobalPrefix()
-          << getFunctionNumber() << '_' << JTI << '_' << MO2.getImm()
-          << "_set_" << MBB->getNumber() << ",(";
-        printBasicBlockLabel(MBB, false, false, false);
-        O << '-' << TAI->getPrivateGlobalPrefix() << "JTI" << getFunctionNumber() 
-          << '_' << JTI << '_' << MO2.getImm() << "+1)\n";
-      } else
-        printPICJumpTableSetLabel(JTI, MO2.getImm(), MBB);
-    }
+    bool isNew = JTSets.insert(MBB);
+
+    if (UseSet && isNew)
+      printPICJumpTableSetLabel(JTI, MO2.getImm(), MBB);
 
     O << JTEntryDirective << ' ';
     if (UseSet)
@@ -952,19 +945,33 @@ void ARMAsmPrinter::printJTBlockOperand(const MachineInstr *MI, int OpNum) {
         O << '-' << TAI->getPrivateGlobalPrefix() << "JTI"
           << getFunctionNumber() << '_' << JTI << '_' << MO2.getImm();
     } else {
-      // FIXME: Temporary workaround for an assembler bug. The assembler isn't
-      // setting the bit zero to 1 even though it is a thumb address.
-      if (NeedBit0)
-        O << '(';
       printBasicBlockLabel(MBB, false, false, false);
-      if (NeedBit0)
-        O << "+1)";
     }
     if (i != e-1)
       O << '\n';
   }
 }
 
+void ARMAsmPrinter::printJT2BlockOperand(const MachineInstr *MI, int OpNum) {
+  const MachineOperand &MO1 = MI->getOperand(OpNum);
+  const MachineOperand &MO2 = MI->getOperand(OpNum+1); // Unique Id
+  unsigned JTI = MO1.getIndex();
+  O << TAI->getPrivateGlobalPrefix() << "JTI" << getFunctionNumber()
+    << '_' << JTI << '_' << MO2.getImm() << ":\n";
+
+  const MachineFunction *MF = MI->getParent()->getParent();
+  const MachineJumpTableInfo *MJTI = MF->getJumpTableInfo();
+  const std::vector<MachineJumpTableEntry> &JT = MJTI->getJumpTables();
+  const std::vector<MachineBasicBlock*> &JTBBs = JT[JTI].MBBs;
+  for (unsigned i = 0, e = JTBBs.size(); i != e; ++i) {
+    MachineBasicBlock *MBB = JTBBs[i];
+    O << "\tb.w ";
+    printBasicBlockLabel(MBB, false, false, false);
+    if (i != e-1)
+      O << '\n';
+  }
+}
+
 
 bool ARMAsmPrinter::PrintAsmOperand(const MachineInstr *MI, unsigned OpNum,
                                     unsigned AsmVariant, const char *ExtraCode){
-- 
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