[libunwind] Fix cfi_register for float registers.

[danielkiss]

Summary

Relaxing the requirement on the register set because getFloatRegister is not const on arm.

[mstorsjo]

This one at least retains the exact same behavior across architectures, but it’s indeed a bit more churn.

[mstorsjo]

Adding the mailing list as subscriber, for visibility

[danielkiss]

abandon in favour of D110731.

libunwind/src/DwarfInstructions.hpp

private:
   typedef typename CFI_Parser<A>::FDE_Info          FDE_Info;
   typedef typename CFI_Parser<A>::CIE_Info          CIE_Info;
 
   static pint_t evaluateExpression(pint_t expression, A &addressSpace,
                                    const R &registers,
                                    pint_t initialStackValue);
   static pint_t getSavedRegister(A &addressSpace, const R &registers,
                                  pint_t cfa, const RegisterLocation &savedReg);
-  static double getSavedFloatRegister(A &addressSpace, const R &registers,
-                                  pint_t cfa, const RegisterLocation &savedReg);
+  static double getSavedFloatRegister(A &addressSpace, R &registers, pint_t cfa,
+                                      const RegisterLocation &savedReg);
   static v128 getSavedVectorRegister(A &addressSpace, const R &registers,
                                   pint_t cfa, const RegisterLocation &savedReg);
 
   static pint_t getCFA(A &addressSpace, const PrologInfo &prolog,
                        const R &registers) {
     if (prolog.cfaRegister != 0)
       return (pint_t)((sint_t)registers.getRegister((int)prolog.cfaRegister) +
              prolog.cfaRegisterOffset);
case CFI_Parser<A>::kRegisterOffsetFromCFA:
     // FIX ME
     break;
   }
   _LIBUNWIND_ABORT("unsupported restore location for register");
 }
 
 template <typename A, typename R>
 double DwarfInstructions<A, R>::getSavedFloatRegister(
-    A &addressSpace, const R &registers, pint_t cfa,
+    A &addressSpace, R &registers, pint_t cfa,
     const RegisterLocation &savedReg) {
   switch (savedReg.location) {
   case CFI_Parser<A>::kRegisterInCFA:
     return addressSpace.getDouble(cfa + (pint_t)savedReg.value);
 
   case CFI_Parser<A>::kRegisterAtExpression:
     return addressSpace.getDouble(
         evaluateExpression((pint_t)savedReg.value, addressSpace,
#define PPC64_ELFV2_R2_OFFSET 24
       }
 #endif
 
       // Return address is address after call site instruction, so setting IP to
       // that does simualates a return.
       newRegisters.setIP(returnAddress);
 
       // Simulate the step by replacing the register set with the new ones.
       registers = newRegisters;
 
       return UNW_STEP_SUCCESS;
     }
   }
   return UNW_EBADFRAME;
 }
 
 template <typename A, typename R>