Avoid nonsence dump string "0xXXXXXX: i1 = Constant<-1>" in output llc -debug

[akuharev]

Summary

"i1 = Constant<-1>" represents signed one bit integer with value 1.
For example when dumping br instruction in IR file.
In dump output all integers are signed.

[akuharev]

Modified test case

lib/Support/APInt.cpp

if (*this == 0) {
     while (*Prefix) {
       Str.push_back(*Prefix);
       ++Prefix;
     };
     Str.push_back('0');
     return;
   }
 
+  // Second, check for a one bit value and just short circuit the logic below.
+  if (*this == 1 && getBitWidth() == 1) {
+    while (*Prefix) {
+      Str.push_back(*Prefix);
+      ++Prefix;
+    };
+    Str.push_back('1');
+    return;
+  }
+
   static const char Digits[] = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ";
 
   if (isSingleWord()) {
     char Buffer[65];
     char *BufPtr = Buffer+65;
 
     uint64_t N;
     if (!Signed) {

test/CodeGen/Generic/signed-one-bit-int.ll

+; RUN: llc -debug %s -o /dev/null 2>&1 | FileCheck %s
+
+define i32 @main() #0 {
+entry:
+  %cmp = icmp eq i32 0, 1
+; CHECK: 0x{{[0-9a-f]+}}: ch = EntryToken
+; CHECK: 0x{{[0-9a-f]+}}: i1 = Constant<1>
+; CHECK: 0x{{[0-9a-f]+}}: ch = BasicBlock<if.end 0x{{[0-9a-f]+}}>
+  br i1 %cmp, label %if.then, label %if.end
+
+if.then: 
+  ret i32 1
+
+if.end:  
+  ret i32 0
+}