MIPS: unwind, don't save/restore hi/lo for R6

HI/LO registers have been removed in MIPSr6. Save and restore them only for pre-R6.

We keep the memory space for the registers so that we can use the same register indexes for
r6 and pre-r6.

Fixes: #60682

Reviewed By: compnerd

Differential Revision: https://reviews.llvm.org/D156283

4 files changed, 25 insertions, 2 deletions

diff --git a/libunwind/include/libunwind.h b/libunwind/include/libunwind.h
index d2ad5ab..b2dae8f 100644
--- a/libunwind/include/libunwind.h
+++ b/libunwind/include/libunwind.h
@@ -876,6 +876,9 @@ enum {
   UNW_MIPS_F29 = 61,
   UNW_MIPS_F30 = 62,
   UNW_MIPS_F31 = 63,
+  // HI,LO have been dropped since r6, we keep them here.
+  // So, when we add DSP/MSA etc, we can use the same register indexes
+  // for r6 and pre-r6.
   UNW_MIPS_HI = 64,
   UNW_MIPS_LO = 65,
 };
diff --git a/libunwind/src/Registers.hpp b/libunwind/src/Registers.hpp
index c7b875d..fb6e04e 100644
--- a/libunwind/src/Registers.hpp
+++ b/libunwind/src/Registers.hpp
@@ -2869,7 +2869,7 @@ inline bool Registers_mips_o32::validRegister(int regNum) const {
     return false;
   if (regNum <= UNW_MIPS_R31)
     return true;
-#if __mips_isa_rev != 6
+#if __mips_isa_rev < 6
   if (regNum == UNW_MIPS_HI)
     return true;
   if (regNum == UNW_MIPS_LO)
@@ -2903,10 +2903,12 @@ inline uint32_t Registers_mips_o32::getRegister(int regNum) const {
     return _registers.__pc;
   case UNW_REG_SP:
     return _registers.__r[29];
+#if __mips_isa_rev < 6
   case UNW_MIPS_HI:
     return _registers.__hi;
   case UNW_MIPS_LO:
     return _registers.__lo;
+#endif
   }
   _LIBUNWIND_ABORT("unsupported mips_o32 register");
 }
@@ -2936,11 +2938,13 @@ inline void Registers_mips_o32::setRegister(int regNum, uint32_t value) {
   case UNW_REG_SP:
     _registers.__r[29] = value;
     return;
+#if __mips_isa_rev < 6
   case UNW_MIPS_HI:
     _registers.__hi = value;
     return;
   case UNW_MIPS_LO:
     _registers.__lo = value;
+#endif
     return;
   }
   _LIBUNWIND_ABORT("unsupported mips_o32 register");
@@ -3120,10 +3124,12 @@ inline const char *Registers_mips_o32::getRegisterName(int regNum) {
     return "$f30";
   case UNW_MIPS_F31:
     return "$f31";
+#if __mips_isa_rev < 6
   case UNW_MIPS_HI:
     return "$hi";
   case UNW_MIPS_LO:
     return "$lo";
+#endif
   default:
     return "unknown register";
   }
@@ -3193,7 +3199,7 @@ inline bool Registers_mips_newabi::validRegister(int regNum) const {
     return false;
   if (regNum <= UNW_MIPS_R31)
     return true;
-#if __mips_isa_rev != 6
+#if __mips_isa_rev < 6
   if (regNum == UNW_MIPS_HI)
     return true;
   if (regNum == UNW_MIPS_LO)
@@ -3212,10 +3218,12 @@ inline uint64_t Registers_mips_newabi::getRegister(int regNum) const {
     return _registers.__pc;
   case UNW_REG_SP:
     return _registers.__r[29];
+#if __mips_isa_rev < 6
   case UNW_MIPS_HI:
     return _registers.__hi;
   case UNW_MIPS_LO:
     return _registers.__lo;
+#endif
   }
   _LIBUNWIND_ABORT("unsupported mips_newabi register");
 }
@@ -3233,12 +3241,14 @@ inline void Registers_mips_newabi::setRegister(int regNum, uint64_t value) {
   case UNW_REG_SP:
     _registers.__r[29] = value;
     return;
+#if __mips_isa_rev < 6
   case UNW_MIPS_HI:
     _registers.__hi = value;
     return;
   case UNW_MIPS_LO:
     _registers.__lo = value;
     return;
+#endif
   }
   _LIBUNWIND_ABORT("unsupported mips_newabi register");
 }
@@ -3417,10 +3427,12 @@ inline const char *Registers_mips_newabi::getRegisterName(int regNum) {
     return "$f30";
   case UNW_MIPS_F31:
     return "$f31";
+#if __mips_isa_rev < 6
   case UNW_MIPS_HI:
     return "$hi";
   case UNW_MIPS_LO:
     return "$lo";
+#endif
   default:
     return "unknown register";
   }
diff --git a/libunwind/src/UnwindRegistersRestore.S b/libunwind/src/UnwindRegistersRestore.S
index 951189e..c4471ea 100644
--- a/libunwind/src/UnwindRegistersRestore.S
+++ b/libunwind/src/UnwindRegistersRestore.S
@@ -993,11 +993,13 @@ DEFINE_LIBUNWIND_FUNCTION(_ZN9libunwind18Registers_mips_o326jumptoEv)
   ldc1  $f31, (4 * 36 + 8 * 31)($4)
 #endif
 #endif
+#if __mips_isa_rev < 6
   // restore hi and lo
   lw    $8, (4 * 33)($4)
   mthi  $8
   lw    $8, (4 * 34)($4)
   mtlo  $8
+#endif
   // r0 is zero
   lw    $1, (4 * 1)($4)
   lw    $2, (4 * 2)($4)
@@ -1054,11 +1056,13 @@ DEFINE_LIBUNWIND_FUNCTION(_ZN9libunwind21Registers_mips_newabi6jumptoEv)
     ldc1 $f\i, (280+8*\i)($4)
   .endr
 #endif
+#if __mips_isa_rev < 6
   // restore hi and lo
   ld    $8, (8 * 33)($4)
   mthi  $8
   ld    $8, (8 * 34)($4)
   mtlo  $8
+#endif
   // r0 is zero
   ld    $1, (8 * 1)($4)
   ld    $2, (8 * 2)($4)
diff --git a/libunwind/src/UnwindRegistersSave.S b/libunwind/src/UnwindRegistersSave.S
index 79f5696..58ffd1b 100644
--- a/libunwind/src/UnwindRegistersSave.S
+++ b/libunwind/src/UnwindRegistersSave.S
@@ -174,11 +174,13 @@ DEFINE_LIBUNWIND_FUNCTION(__unw_getcontext)
   sw    $31, (4 * 31)($4)
   # Store return address to pc
   sw    $31, (4 * 32)($4)
+#if __mips_isa_rev < 6
   # hi and lo
   mfhi  $8
   sw    $8,  (4 * 33)($4)
   mflo  $8
   sw    $8,  (4 * 34)($4)
+#endif
 #ifdef __mips_hard_float
 #if __mips_fpr != 64
   sdc1  $f0, (4 * 36 + 8 * 0)($4)
@@ -255,11 +257,13 @@ DEFINE_LIBUNWIND_FUNCTION(__unw_getcontext)
   .endr
   # Store return address to pc
   sd    $31, (8 * 32)($4)
+#if __mips_isa_rev < 6
   # hi and lo
   mfhi  $8
   sd    $8,  (8 * 33)($4)
   mflo  $8
   sd    $8,  (8 * 34)($4)
+#endif
 #ifdef __mips_hard_float
   .irp i,FROM_0_TO_31
     sdc1 $f\i, (280+8*\i)($4)