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.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@77024 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Target/ARM/AsmPrinter/ARMAsmPrinter.cpp b/lib/Target/ARM/AsmPrinter/ARMAsmPrinter.cpp
index 4d21d5c..cffbecd 100644
--- a/lib/Target/ARM/AsmPrinter/ARMAsmPrinter.cpp
+++ b/lib/Target/ARM/AsmPrinter/ARMAsmPrinter.cpp
@@ -160,6 +160,7 @@
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::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 @@
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 @@
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){