[ADT][bugfix] Fixed extra leading zero in uhextostr

fixed bug: if fixed-width mode uhextostr() is used with value zero, it prints
extra '0' character.

Author: Dmitry Bushev

llvm/include/llvm/ADT/StringExtras.h

@@ -179,7 +179,8 @@ inline std::string utohexstr(uint64_t X, bool LowerCase = false,
   char Buffer[17];
   char *BufPtr = std::end(Buffer);
 
-  if (X == 0) *--BufPtr = '0';
+  if (X == 0 && !Width)
+    *--BufPtr = '0';
 
   for (unsigned i = 0; Width ? (i < Width) : X; ++i) {
     unsigned char Mod = static_cast<unsigned char>(X) & 15;

llvm/unittests/ADT/StringExtrasTest.cpp

@@ -144,6 +144,7 @@ TEST(StringExtrasTest, ToAndFromHex) {
 }
 
 TEST(StringExtrasTest, UINT64ToHex) {
+  EXPECT_EQ(utohexstr(0x0u, false, 2), "00");
   EXPECT_EQ(utohexstr(0xA0u), "A0");
   EXPECT_EQ(utohexstr(0xA0u, false, 4), "00A0");
   EXPECT_EQ(utohexstr(0xA0u, false, 8), "000000A0");