Change MCRegisterInfo::getLLVMRegNum() not to assert on unknown register.

[friss]

Summary

I want to use this method in llvm-dwarfdump to be able to pretty
print register names in dwarf expressions. As the data I'll feed
to the method comes directly from the binary file, it might be
anything and I'd like to avoid asserting when an unknown register
number is requested.

This patch makes the method return -1 when the register isn't found.
The new behavior is the same as its inverse function getDwarfRegNum.
Note that although this method returns an 'int', each and every user I
could find stores the result in an 'unsigned' variable. Would it
make sense to change the method return type to unsigned? Should the
assert be kept and propagated to the callers? Any other suggestion
to achieve what I want?

[friss]

Keep the current asserting behavior in getLLVMRegNum() but
implement it in terms of a new non-asserting tryGetLLVMRegNum().

[dblaikie]

Looks fine to me (not sure if that's it's not readily unit testable... oh well - I guess your use case will follow swiftly after)

[Eugene.Zelenko]

Looks like patch was not committed.

include/llvm/MC/MCRegisterInfo.h

public:
 
   /// \brief Map a target register to an equivalent dwarf register
   /// number.  Returns -1 if there is no equivalent value.  The second
   /// parameter allows targets to use different numberings for EH info and
   /// debugging info.
   int getDwarfRegNum(unsigned RegNum, bool isEH) const;
 
   /// \brief Map a dwarf register back to a target register.
-  int getLLVMRegNum(unsigned RegNum, bool isEH) const;
+  /// This method might assert if no mapping exists.
+  unsigned getLLVMRegNum(unsigned RegNum, bool isEH) const {
+    int LLVMRegNum = tryGetLLVMRegNum(RegNum, isEH);
+    assert(LLVMRegNum != -1 && "Invalid RegNum");
+    return LLVMRegNum;
+  }
+
+  /// \brief Map a Dwarf register back to a target register.
+  /// \returns the corresponding LLVM register number or -1 if the
+  /// passed Dwarf register is invalid.
+  int tryGetLLVMRegNum(unsigned RegNum, bool isEH) const;
 
   /// \brief Map a target register to an equivalent SEH register
   /// number.  Returns LLVM register number if there is no equivalent value.
   int getSEHRegNum(unsigned RegNum) const;
 
   regclass_iterator regclass_begin() const { return Classes; }
   regclass_iterator regclass_end() const { return Classes+NumClasses; }
 

lib/MC/MCRegisterInfo.cpp

int MCRegisterInfo::getDwarfRegNum(unsigned RegNum, bool isEH) const {
 
   DwarfLLVMRegPair Key = { RegNum, 0 };
   const DwarfLLVMRegPair *I = std::lower_bound(M, M+Size, Key);
   if (I == M+Size || I->FromReg != RegNum)
     return -1;
   return I->ToReg;
 }
 
-int MCRegisterInfo::getLLVMRegNum(unsigned RegNum, bool isEH) const {
+int MCRegisterInfo::tryGetLLVMRegNum(unsigned RegNum, bool isEH) const {
   const DwarfLLVMRegPair *M = isEH ? EHDwarf2LRegs : Dwarf2LRegs;
   unsigned Size = isEH ? EHDwarf2LRegsSize : Dwarf2LRegsSize;
 
   DwarfLLVMRegPair Key = { RegNum, 0 };
   const DwarfLLVMRegPair *I = std::lower_bound(M, M+Size, Key);
-  assert(I != M+Size && I->FromReg == RegNum && "Invalid RegNum");
+  if (I == M+Size || I->FromReg != RegNum)
+    return -1;
   return I->ToReg;
 }
 
 int MCRegisterInfo::getSEHRegNum(unsigned RegNum) const {
   const DenseMap<unsigned, int>::const_iterator I = L2SEHRegs.find(RegNum);
   if (I == L2SEHRegs.end()) return (int)RegNum;
   return I->second;
 }