TableGen: Fix ASAN error

Summary:
As a bonus, this arguably improves the code by making it simpler.

gcc 8 on Ubuntu 18.10 reports the following:

==39667==ERROR: AddressSanitizer: stack-use-after-scope on address 0x7fffffff8ae0 at pc 0x555555dbfc68 bp 0x7fffffff8760 sp 0x7fffffff8750
WRITE of size 8 at 0x7fffffff8ae0 thread T0
    #0 0x555555dbfc67 in std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >::_Alloc_hider::_Alloc_hider(char*, std::allocator<char>&&) /usr/include/c++/8/bits/basic_string.h:149
    rust-lang#1 0x555555dbfc67 in std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >::basic_string(std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >&&) /usr/include/c++/8/bits/basic_string.h:542
    rust-lang#2 0x555555dbfc67 in std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > std::operator+<char, std::char_traits<char>, std::allocator<char> >(char const*, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >&&) /usr/include/c++/8/bits/basic_string.h:6009
    rust-lang#3 0x555555dbfc67 in searchableFieldType /home/nha/amd/build/san/llvm-src/utils/TableGen/SearchableTableEmitter.cpp:168
    (...)

Address 0x7fffffff8ae0 is located in stack of thread T0 at offset 864 in frame
    #0 0x555555dbef3f in searchableFieldType /home/nha/amd/build/san/llvm-src/utils/TableGen/SearchableTableEmitter.cpp:148

Reviewers: fhahn, simon_tatham, kparzysz

Subscribers: llvm-commits

Differential Revision: https://reviews.llvm.org/D53931

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@345749 91177308-0d34-0410-b5e6-96231b3b80d8

Author: nhaehnle

utils/TableGen/SearchableTableEmitter.cpp

@@ -155,17 +155,15 @@ class SearchableTableEmitter {
     } else if (BitsRecTy *BI = dyn_cast<BitsRecTy>(Field.RecType)) {
       unsigned NumBits = BI->getNumBits();
       if (NumBits <= 8)
-        NumBits = 8;
-      else if (NumBits <= 16)
-        NumBits = 16;
-      else if (NumBits <= 32)
-        NumBits = 32;
-      else if (NumBits <= 64)
-        NumBits = 64;
-      else
-        PrintFatalError(Twine("bitfield '") + Field.Name +
-                        "' too large to search");
-      return "uint" + utostr(NumBits) + "_t";
+        return "uint8_t";
+      if (NumBits <= 16)
+        return "uint16_t";
+      if (NumBits <= 32)
+        return "uint32_t";
+      if (NumBits <= 64)
+        return "uint64_t";
+      PrintFatalError(Twine("bitfield '") + Field.Name +
+                      "' too large to search");
     } else if (Field.Enum || Field.IsIntrinsic || Field.IsInstruction)
       return "unsigned";
     PrintFatalError(Twine("Field '") + Field.Name + "' has unknown type '" +