[AArch64] Define subtarget feature "reserve-x18", which is used to decide

whether register x18 should be reserved.

This change is needed because we cannot use a backend option to set
cl::opt "aarch64-reserve-x18" when doing LTO.

Out-of-tree projects currently using cl::opt option "-aarch64-reserve-x18"
to reserve x18 should make changes to add subtarget feature "reserve-x18"
to the IR.

rdar://problem/21529937

Differential Revision: http://reviews.llvm.org/D11463

llvm-svn: 243186

4 files changed, 18 insertions, 10 deletions

diff --git a/llvm/lib/Target/AArch64/AArch64.td b/llvm/lib/Target/AArch64/AArch64.td
index 9a7d6c884db..23e0647b34b 100644
--- a/llvm/lib/Target/AArch64/AArch64.td
+++ b/llvm/lib/Target/AArch64/AArch64.td
@@ -40,6 +40,10 @@ def FeatureZCRegMove : SubtargetFeature<"zcm", "HasZeroCycleRegMove", "true",
 def FeatureZCZeroing : SubtargetFeature<"zcz", "HasZeroCycleZeroing", "true",
                                         "Has zero-cycle zeroing instructions">;
 
+def FeatureReserveX18 : SubtargetFeature<"reserve-x18", "ReserveX18", "true",
+                                         "Reserve X18, making it unavailable "
+                                         "as a GPR">;
+
 //===----------------------------------------------------------------------===//
 // Architectures.
 //
diff --git a/llvm/lib/Target/AArch64/AArch64RegisterInfo.cpp b/llvm/lib/Target/AArch64/AArch64RegisterInfo.cpp
index d61be5adb88..d2d5205cf2d 100644
--- a/llvm/lib/Target/AArch64/AArch64RegisterInfo.cpp
+++ b/llvm/lib/Target/AArch64/AArch64RegisterInfo.cpp
@@ -34,10 +34,6 @@ using namespace llvm;
 #define GET_REGINFO_TARGET_DESC
 #include "AArch64GenRegisterInfo.inc"
 
-static cl::opt<bool>
-ReserveX18("aarch64-reserve-x18", cl::Hidden,
-          cl::desc("Reserve X18, making it unavailable as GPR"));
-
 AArch64RegisterInfo::AArch64RegisterInfo(const Triple &TT)
     : AArch64GenRegisterInfo(AArch64::LR), TT(TT) {}
 
@@ -104,7 +100,7 @@ AArch64RegisterInfo::getReservedRegs(const MachineFunction &MF) const {
     Reserved.set(AArch64::W29);
   }
 
-  if (TT.isOSDarwin() || ReserveX18) {
+  if (TT.isOSDarwin() || MF.getSubtarget<AArch64Subtarget>().isX18Reserved()) {
     Reserved.set(AArch64::X18); // Platform register
     Reserved.set(AArch64::W18);
   }
@@ -131,7 +127,8 @@ bool AArch64RegisterInfo::isReservedReg(const MachineFunction &MF,
     return true;
   case AArch64::X18:
   case AArch64::W18:
-    return TT.isOSDarwin() || ReserveX18;
+    return TT.isOSDarwin() ||
+           MF.getSubtarget<AArch64Subtarget>().isX18Reserved();
   case AArch64::FP:
   case AArch64::W29:
     return TFI->hasFP(MF) || TT.isOSDarwin();
@@ -402,9 +399,11 @@ unsigned AArch64RegisterInfo::getRegPressureLimit(const TargetRegisterClass *RC,
   case AArch64::GPR32commonRegClassID:
   case AArch64::GPR64commonRegClassID:
     return 32 - 1                                // XZR/SP
-           - (TFI->hasFP(MF) || TT.isOSDarwin()) // FP
-           - (TT.isOSDarwin() || ReserveX18) // X18 reserved as platform register
-           - hasBasePointer(MF);           // X19
+      - (TFI->hasFP(MF) || TT.isOSDarwin()) // FP
+      - (TT.isOSDarwin() ||
+         MF.getSubtarget<AArch64Subtarget>()
+             .isX18Reserved()) // X18 reserved as platform register
+      - hasBasePointer(MF);    // X19
   case AArch64::FPR8RegClassID:
   case AArch64::FPR16RegClassID:
   case AArch64::FPR32RegClassID:
diff --git a/llvm/lib/Target/AArch64/AArch64Subtarget.cpp b/llvm/lib/Target/AArch64/AArch64Subtarget.cpp
index 486efd6ce3a..7ef1f9d0e3f 100644
--- a/llvm/lib/Target/AArch64/AArch64Subtarget.cpp
+++ b/llvm/lib/Target/AArch64/AArch64Subtarget.cpp
@@ -48,7 +48,8 @@ AArch64Subtarget::AArch64Subtarget(const Triple &TT, const std::string &CPU,
     : AArch64GenSubtargetInfo(TT, CPU, FS), ARMProcFamily(Others),
       HasV8_1aOps(false), HasFPARMv8(false), HasNEON(false), HasCrypto(false),
       HasCRC(false), HasZeroCycleRegMove(false), HasZeroCycleZeroing(false),
-      IsLittle(LittleEndian), CPUString(CPU), TargetTriple(TT), FrameLowering(),
+      ReserveX18(false), IsLittle(LittleEndian), CPUString(CPU),
+      TargetTriple(TT), FrameLowering(),
       InstrInfo(initializeSubtargetDependencies(FS)), TSInfo(),
       TLInfo(TM, *this) {}
 
diff --git a/llvm/lib/Target/AArch64/AArch64Subtarget.h b/llvm/lib/Target/AArch64/AArch64Subtarget.h
index 6bb06942306..19334c29c7b 100644
--- a/llvm/lib/Target/AArch64/AArch64Subtarget.h
+++ b/llvm/lib/Target/AArch64/AArch64Subtarget.h
@@ -51,6 +51,9 @@ protected:
   // HasZeroCycleZeroing - Has zero-cycle zeroing instructions.
   bool HasZeroCycleZeroing;
 
+  // ReserveX18 - X18 is not available as a general purpose register.
+  bool ReserveX18;
+
   bool IsLittle;
 
   /// CPUString - String name of used CPU.
@@ -101,6 +104,7 @@ public:
 
   bool hasZeroCycleZeroing() const { return HasZeroCycleZeroing; }
 
+  bool isX18Reserved() const { return ReserveX18; }
   bool hasFPARMv8() const { return HasFPARMv8; }
   bool hasNEON() const { return HasNEON; }
   bool hasCrypto() const { return HasCrypto; }