Replace PROLOG_LABEL with a new CFI_INSTRUCTION.

The old system was fairly convoluted:
* A temporary label was created.
* A single PROLOG_LABEL was created with it.
* A few MCCFIInstructions were created with the same label.

The semantics were that the cfi instructions were mapped to the PROLOG_LABEL
via the temporary label. The output position was that of the PROLOG_LABEL.
The temporary label itself was used only for doing the mapping.

The new CFI_INSTRUCTION has a 1:1 mapping to MCCFIInstructions and points to
one by holding an index into the CFI instructions of this function.

I did consider removing MMI.getFrameInstructions completelly and having
CFI_INSTRUCTION own a MCCFIInstruction, but MCCFIInstructions have non
trivial constructors and destructors and are somewhat big, so the this setup
is probably better.

The net result is that we don't create temporary labels that are never used.

llvm-svn: 203204

1 files changed, 20 insertions, 23 deletions

diff --git a/llvm/lib/Target/SystemZ/SystemZFrameLowering.cpp b/llvm/lib/Target/SystemZ/SystemZFrameLowering.cpp
index f084560d8c5..c856955f7eb 100644
--- a/llvm/lib/Target/SystemZ/SystemZFrameLowering.cpp
+++ b/llvm/lib/Target/SystemZ/SystemZFrameLowering.cpp
@@ -333,15 +333,14 @@ void SystemZFrameLowering::emitPrologue(MachineFunction &MF) const {
       llvm_unreachable("Couldn't skip over GPR saves");
 
     // Add CFI for the GPR saves.
-    MCSymbol *GPRSaveLabel = MMI.getContext().CreateTempSymbol();
-    BuildMI(MBB, MBBI, DL,
-            ZII->get(TargetOpcode::PROLOG_LABEL)).addSym(GPRSaveLabel);
     for (auto &Save : CSI) {
       unsigned Reg = Save.getReg();
       if (SystemZ::GR64BitRegClass.contains(Reg)) {
         int64_t Offset = SPOffsetFromCFA + RegSpillOffsets[Reg];
-        MMI.addFrameInst(MCCFIInstruction::createOffset(
-            GPRSaveLabel, MRI->getDwarfRegNum(Reg, true), Offset));
+        unsigned CFIIndex = MMI.addFrameInst(MCCFIInstruction::createOffset(
+            nullptr, MRI->getDwarfRegNum(Reg, true), Offset));
+        BuildMI(MBB, MBBI, DL, ZII->get(TargetOpcode::CFI_INSTRUCTION))
+            .addCFIIndex(CFIIndex);
       }
     }
   }
@@ -353,11 +352,10 @@ void SystemZFrameLowering::emitPrologue(MachineFunction &MF) const {
     emitIncrement(MBB, MBBI, DL, SystemZ::R15D, Delta, ZII);
 
     // Add CFI for the allocation.
-    MCSymbol *AdjustSPLabel = MMI.getContext().CreateTempSymbol();
-    BuildMI(MBB, MBBI, DL, ZII->get(TargetOpcode::PROLOG_LABEL))
-      .addSym(AdjustSPLabel);
-    MMI.addFrameInst(MCCFIInstruction::createDefCfaOffset(
-        AdjustSPLabel, SPOffsetFromCFA + Delta));
+    unsigned CFIIndex = MMI.addFrameInst(
+        MCCFIInstruction::createDefCfaOffset(nullptr, SPOffsetFromCFA + Delta));
+    BuildMI(MBB, MBBI, DL, ZII->get(TargetOpcode::CFI_INSTRUCTION))
+        .addCFIIndex(CFIIndex);
     SPOffsetFromCFA += Delta;
   }
 
@@ -367,12 +365,11 @@ void SystemZFrameLowering::emitPrologue(MachineFunction &MF) const {
       .addReg(SystemZ::R15D);
 
     // Add CFI for the new frame location.
-    MCSymbol *SetFPLabel = MMI.getContext().CreateTempSymbol();
-    BuildMI(MBB, MBBI, DL, ZII->get(TargetOpcode::PROLOG_LABEL))
-      .addSym(SetFPLabel);
     unsigned HardFP = MRI->getDwarfRegNum(SystemZ::R11D, true);
-    MMI.addFrameInst(
-        MCCFIInstruction::createDefCfaRegister(SetFPLabel, HardFP));
+    unsigned CFIIndex = MMI.addFrameInst(
+        MCCFIInstruction::createDefCfaRegister(nullptr, HardFP));
+    BuildMI(MBB, MBBI, DL, ZII->get(TargetOpcode::CFI_INSTRUCTION))
+        .addCFIIndex(CFIIndex);
 
     // Mark the FramePtr as live at the beginning of every block except
     // the entry block.  (We'll have marked R11 as live on entry when
@@ -382,7 +379,7 @@ void SystemZFrameLowering::emitPrologue(MachineFunction &MF) const {
   }
 
   // Skip over the FPR saves.
-  MCSymbol *FPRSaveLabel = 0;
+  SmallVector<unsigned, 8> CFIIndexes;
   for (auto &Save : CSI) {
     unsigned Reg = Save.getReg();
     if (SystemZ::FP64BitRegClass.contains(Reg)) {
@@ -394,19 +391,19 @@ void SystemZFrameLowering::emitPrologue(MachineFunction &MF) const {
         llvm_unreachable("Couldn't skip over FPR save");
 
       // Add CFI for the this save.
-      if (!FPRSaveLabel)
-        FPRSaveLabel = MMI.getContext().CreateTempSymbol();
       unsigned DwarfReg = MRI->getDwarfRegNum(Reg, true);
       int64_t Offset = getFrameIndexOffset(MF, Save.getFrameIdx());
-      MMI.addFrameInst(MCCFIInstruction::createOffset(
-          FPRSaveLabel, DwarfReg, SPOffsetFromCFA + Offset));
+      unsigned CFIIndex = MMI.addFrameInst(MCCFIInstruction::createOffset(
+          nullptr, DwarfReg, SPOffsetFromCFA + Offset));
+      CFIIndexes.push_back(CFIIndex);
     }
   }
   // Complete the CFI for the FPR saves, modelling them as taking effect
   // after the last save.
-  if (FPRSaveLabel)
-    BuildMI(MBB, MBBI, DL, ZII->get(TargetOpcode::PROLOG_LABEL))
-      .addSym(FPRSaveLabel);
+  for (auto CFIIndex : CFIIndexes) {
+    BuildMI(MBB, MBBI, DL, ZII->get(TargetOpcode::CFI_INSTRUCTION))
+        .addCFIIndex(CFIIndex);
+  }
 }
 
 void SystemZFrameLowering::emitEpilogue(MachineFunction &MF,