Add register Mips::GP to the list of reserved registers if target is bare-metal

to prevent it from being clobbered. mips uses $gp to access small data section.

This bug was originally reported by Carl Norum.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@162340 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Target/Mips/MipsISelLowering.cpp

@@ -1578,8 +1578,8 @@ SDValue MipsTargetLowering::LowerGlobalAddress(SDValue Op,
       SDValue GA = DAG.getTargetGlobalAddress(GV, dl, MVT::i32, 0,
                                               MipsII::MO_GPREL);
       SDValue GPRelNode = DAG.getNode(MipsISD::GPRel, dl, VTs, &GA, 1);
-      SDValue GOT = DAG.getGLOBAL_OFFSET_TABLE(MVT::i32);
+      SDValue GPReg = DAG.getRegister(Mips::GP, MVT::i32);
-      return DAG.getNode(ISD::ADD, dl, MVT::i32, GOT, GPRelNode);
+      return DAG.getNode(ISD::ADD, dl, MVT::i32, GPReg, GPRelNode);
     }
     // %hi/%lo relocation
     SDValue GAHi = DAG.getTargetGlobalAddress(GV, dl, MVT::i32, 0,

lib/Target/Mips/MipsRegisterInfo.cpp

@@ -131,6 +131,12 @@ getReservedRegs(const MachineFunction &MF) const {
     Reserved.set(Mips::RA_64);
   }
 
+  // Reserve GP if small section is used.
+  if (Subtarget.useSmallSection()) {
+    Reserved.set(Mips::GP);
+    Reserved.set(Mips::GP_64);
+  }
+
   return Reserved;
 }
 

lib/Target/Mips/MipsSubtarget.cpp

@@ -25,7 +25,8 @@ using namespace llvm;
 void MipsSubtarget::anchor() { }
 
 MipsSubtarget::MipsSubtarget(const std::string &TT, const std::string &CPU,
-                             const std::string &FS, bool little) :
+                             const std::string &FS, bool little,
+                             Reloc::Model RM) :
   MipsGenSubtargetInfo(TT, CPU, FS),
   MipsArchVersion(Mips32), MipsABI(UnknownABI), IsLittle(little),
   IsSingleFloat(false), IsFP64bit(false), IsGP64bit(false), HasVFPU(false),
@@ -54,6 +55,9 @@ MipsSubtarget::MipsSubtarget(const std::string &TT, const std::string &CPU,
   // Is the target system Linux ?
   if (TT.find("linux") == std::string::npos)
     IsLinux = false;
+
+  // Set UseSmallSection.
+  UseSmallSection = !IsLinux && (RM == Reloc::Static);
 }
 
 bool

lib/Target/Mips/MipsSubtarget.h

@@ -65,6 +65,9 @@ protected:
   // isLinux - Target system is Linux. Is false we consider ELFOS for now.
   bool IsLinux;
 
+  // UseSmallSection - Small section is used.
+  bool UseSmallSection;
+
   /// Features related to the presence of specific instructions.
 
   // HasSEInReg - SEB and SEH (signext in register) instructions.
@@ -109,7 +112,7 @@ public:
   /// This constructor initializes the data members to match that
   /// of the specified triple.
   MipsSubtarget(const std::string &TT, const std::string &CPU,
-                const std::string &FS, bool little);
+                const std::string &FS, bool little, Reloc::Model RM);
 
   /// ParseSubtargetFeatures - Parses features string setting specified
   /// subtarget options.  Definition of function is auto generated by tblgen.
@@ -133,6 +136,7 @@ public:
   bool inMips16Mode() const { return InMips16Mode; }
   bool isAndroid() const { return IsAndroid; }
   bool isLinux() const { return IsLinux; }
+  bool useSmallSection() const { return UseSmallSection; }
 
   bool hasStandardEncoding() const { return !inMips16Mode(); }
 

lib/Target/Mips/MipsTargetMachine.cpp

@@ -42,7 +42,7 @@ MipsTargetMachine(const Target &T, StringRef TT,
                   CodeGenOpt::Level OL,
                   bool isLittle)
   : LLVMTargetMachine(T, TT, CPU, FS, Options, RM, CM, OL),
-    Subtarget(TT, CPU, FS, isLittle),
+    Subtarget(TT, CPU, FS, isLittle, RM),
     DataLayout(isLittle ?
                (Subtarget.isABI_N64() ?
                 "e-p:64:64:64-i8:8:32-i16:16:32-i64:64:64-f128:128:128-n32" :

lib/Target/Mips/MipsTargetObjectFile.cpp

@@ -60,9 +60,10 @@ bool MipsTargetObjectFile::
 IsGlobalInSmallSection(const GlobalValue *GV, const TargetMachine &TM,
                        SectionKind Kind) const {
 
-  // Only use small section for non linux targets.
   const MipsSubtarget &Subtarget = TM.getSubtarget<MipsSubtarget>();
-  if (Subtarget.isLinux())
+
+  // Return if small section is not available.
+  if (!Subtarget.useSmallSection())
     return false;
 
   // Only global variables, not functions.

test/CodeGen/Mips/small-section-reserve-gp.ll

@@ -0,0 +1,12 @@
+; RUN: llc -mtriple=mipsel-sde-elf -march=mipsel -relocation-model=static < %s \
+; RUN: | FileCheck %s
+
+@i = internal unnamed_addr global i32 0, align 4
+
+define i32 @geti() nounwind readonly {
+entry:
+; CHECK: addiu ${{[0-9]+}}, $gp, %gp_rel(i)
+  %0 = load i32* @i, align 4
+  ret i32 %0
+}
+