[llvm] Do not zero out write_unsigned_impl internal buffer

[serge-sans-paille]

Summary

Current implementation uselessly calls memset on its internal buffer
while it does not read the non overwritten part.

[mehdi_amini]

How did you find this? Just random audit of the code?

[serge-sans-paille]

In D142464#4081513, @mehdi_amini wrote:

How did you find this? Just random audit of the code?

It started with random profiling and then I stumbled on that function and then...

llvm/lib/Support/NativeFormatting.cpp

 }
 
 template <typename T>
 static void write_unsigned_impl(raw_ostream &S, T N, size_t MinDigits,
                                 IntegerStyle Style, bool IsNegative) {
   static_assert(std::is_unsigned_v<T>, "Value is not unsigned!");
 
   char NumberBuffer[128];
-  std::memset(NumberBuffer, '0', sizeof(NumberBuffer));
-
-  size_t Len = 0;
-  Len = format_to_buffer(N, NumberBuffer);
+  size_t Len = format_to_buffer(N, NumberBuffer);
 
   if (IsNegative)
     S << '-';
 
   if (Len < MinDigits && Style != IntegerStyle::Number) {
     for (size_t I = Len; I < MinDigits; ++I)
       S << '0';
   }

llvm/unittests/Support/NativeFormatTests.cpp

std::string format_number(double D, FloatStyle Style,
   return S;
 }
 
 // Test basic number formatting with various styles and default width and
 // precision.
 TEST(NativeFormatTest, BasicIntegerTests) {
   // Simple integers with no decimal.
   EXPECT_EQ("0", format_number(0, IntegerStyle::Integer));
+  EXPECT_EQ("1", format_number(1, IntegerStyle::Integer));
+  EXPECT_EQ("-1", format_number(-1, IntegerStyle::Integer));
   EXPECT_EQ("2425", format_number(2425, IntegerStyle::Integer));
   EXPECT_EQ("-2425", format_number(-2425, IntegerStyle::Integer));
 
   EXPECT_EQ("0", format_number(0LL, IntegerStyle::Integer));
   EXPECT_EQ("257257257235709",
             format_number(257257257235709LL, IntegerStyle::Integer));
   EXPECT_EQ("-257257257235709",
             format_number(-257257257235709LL, IntegerStyle::Integer));