Avoid accessing LLVM/DWARF register mappings if undefined

Summary:
If the backend does not define LLVM/DWARF register mappings, the associated
variables are undefined since the map initializer is called by auto-generated
TableGen routines. This patch initializes the pointers and sizes to nullptr
and zero, respectively, and checks that they are valid before searching
for a mapping.

Reviewers: grosbach, dschuff

Subscribers: llvm-commits

Differential Revision: https://reviews.llvm.org/D23458

llvm-svn: 278574

2 files changed, 14 insertions, 0 deletions

diff --git a/llvm/include/llvm/MC/MCRegisterInfo.h b/llvm/include/llvm/MC/MCRegisterInfo.h
index 548280614e9..1d3c64a8ef5 100644
--- a/llvm/include/llvm/MC/MCRegisterInfo.h
+++ b/llvm/include/llvm/MC/MCRegisterInfo.h
@@ -271,6 +271,16 @@ public:
     NumSubRegIndices = NumIndices;
     SubRegIdxRanges = SubIdxRanges;
     RegEncodingTable = RET;
+
+    // Initialize DWARF register mapping variables
+    EHL2DwarfRegs = nullptr;
+    EHL2DwarfRegsSize = 0;
+    L2DwarfRegs = nullptr;
+    L2DwarfRegsSize = 0;
+    EHDwarf2LRegs = nullptr;
+    EHDwarf2LRegsSize = 0;
+    Dwarf2LRegs = nullptr;
+    Dwarf2LRegsSize = 0;
   }
 
   /// \brief Used to initialize LLVM register to Dwarf
diff --git a/llvm/lib/MC/MCRegisterInfo.cpp b/llvm/lib/MC/MCRegisterInfo.cpp
index c76bb646c12..3d0f30d306c 100644
--- a/llvm/lib/MC/MCRegisterInfo.cpp
+++ b/llvm/lib/MC/MCRegisterInfo.cpp
@@ -62,6 +62,8 @@ int MCRegisterInfo::getDwarfRegNum(unsigned RegNum, bool isEH) const {
   const DwarfLLVMRegPair *M = isEH ? EHL2DwarfRegs : L2DwarfRegs;
   unsigned Size = isEH ? EHL2DwarfRegsSize : L2DwarfRegsSize;
 
+  if (!M)
+    return -1;
   DwarfLLVMRegPair Key = { RegNum, 0 };
   const DwarfLLVMRegPair *I = std::lower_bound(M, M+Size, Key);
   if (I == M+Size || I->FromReg != RegNum)
@@ -73,6 +75,8 @@ int MCRegisterInfo::getLLVMRegNum(unsigned RegNum, bool isEH) const {
   const DwarfLLVMRegPair *M = isEH ? EHDwarf2LRegs : Dwarf2LRegs;
   unsigned Size = isEH ? EHDwarf2LRegsSize : Dwarf2LRegsSize;
 
+  if (!M)
+    return -1;
   DwarfLLVMRegPair Key = { RegNum, 0 };
   const DwarfLLVMRegPair *I = std::lower_bound(M, M+Size, Key);
   assert(I != M+Size && I->FromReg == RegNum && "Invalid RegNum");