[Demangle] Add prepend functionality to OutputString

[ljmf00]

Summary

Implement the functionallity of prepend, required by D demangler.
Please read discussion https://reviews.llvm.org/D111414 for context.
See also https://reviews.llvm.org/D111947 .

[dblaikie]

Looks alright - guess some other boundary testing could be done (testing without anything in the buffer, testing when prepend causes the buffer to grow V when it's already big enough) but it's probably fine as-is.

libcxxabi/src/demangle/Utility.h

101

Could probably skip this. Falls out naturally from the implementation.

103–105

Could use memmove for this?

[ljmf00]

I added more tests to cover the requested situations. I also forgot to add a free after a malloc on the testsuite. I also changed the manual for loop to memmove to benefit from optimized implementations.

[ljmf00]

Just ran clang-format

[ljmf00]

Renamed OutputString test to OutputBuffer test

[Geod24]

LGTM

[ljmf00]

@dblaikie I changed what you requested, which includes the use of memmove and adding some tests to cover empty buffers and reinsertion after resetting the position. Can you re-review please?

[dblaikie]

Looks good, thanks!

[ljmf00]

In D111948#3085316, @dblaikie wrote:

Looks good, thanks!

Can you or someone with permission, land it? Thanks :)

[dblaikie]

I'm having trouble applying this patch locally - I get:

$ arc patch D111948
Created and checked out branch arcpatch-D111948.
Created and checked out branch arcpatch-D111947.
Checking patch llvm/unittests/Demangle/OutputStreamTest.cpp => llvm/unittests/Demangle/OutputBufferTest.cpp...
Checking patch llvm/unittests/Demangle/ItaniumDemangleTest.cpp...
Checking patch llvm/unittests/Demangle/CMakeLists.txt...
Checking patch llvm/lib/Demangle/RustDemangle.cpp...
Checking patch llvm/lib/Demangle/MicrosoftDemangleNodes.cpp...
Checking patch llvm/lib/Demangle/MicrosoftDemangle.cpp...
Checking patch llvm/lib/Demangle/ItaniumDemangle.cpp...
Checking patch llvm/include/llvm/Demangle/Utility.h...
Checking patch llvm/include/llvm/Demangle/MicrosoftDemangleNodes.h...
Checking patch llvm/include/llvm/Demangle/ItaniumDemangle.h...
Checking patch libcxxabi/src/demangle/Utility.h...
Checking patch libcxxabi/src/demangle/ItaniumDemangle.h...
Applied patch llvm/unittests/Demangle/OutputStreamTest.cpp => llvm/unittests/Demangle/OutputBufferTest.cpp cleanly.
Applied patch llvm/unittests/Demangle/ItaniumDemangleTest.cpp cleanly.
Applied patch llvm/unittests/Demangle/CMakeLists.txt cleanly.
Applied patch llvm/lib/Demangle/RustDemangle.cpp cleanly.
Applied patch llvm/lib/Demangle/MicrosoftDemangleNodes.cpp cleanly.
Applied patch llvm/lib/Demangle/MicrosoftDemangle.cpp cleanly.
Applied patch llvm/lib/Demangle/ItaniumDemangle.cpp cleanly.
Applied patch llvm/include/llvm/Demangle/Utility.h cleanly.
Applied patch llvm/include/llvm/Demangle/MicrosoftDemangleNodes.h cleanly.
Applied patch llvm/include/llvm/Demangle/ItaniumDemangle.h cleanly.
Applied patch libcxxabi/src/demangle/Utility.h cleanly.
Applied patch libcxxabi/src/demangle/ItaniumDemangle.h cleanly.

 Cherry Pick Failed!
Exception
Command failed with error #1!
COMMAND
git cherry-pick 'arcpatch-D111947'

STDOUT
On branch arcpatch-D111948
You are currently cherry-picking commit f03e9f1cbed8.
  (all conflicts fixed: run "git cherry-pick --continue")
  (use "git cherry-pick --skip" to skip this patch)
  (use "git cherry-pick --abort" to cancel the cherry-pick operation)

nothing to commit, working tree clean


STDERR
The previous cherry-pick is now empty, possibly due to conflict resolution.
If you wish to commit it anyway, use:

    git commit --allow-empty

Otherwise, please use 'git cherry-pick --skip'

(Run with `--trace` for a full exception trace.)

Perhaps it needs to be rebased or something?

[ljmf00]

In D111948#3088563, @dblaikie wrote:

Perhaps it needs to be rebased or something?

Should be good now. For some reason, adding the rename patch to the parent patch stack did that. I reproduced the arc patch D111948 and it works now. I rebased anyway.

libcxxabi/src/demangle/Utility.h

public:
   OutputBuffer &operator+=(char C) {
     grow(1);
     Buffer[CurrentPosition++] = C;
     return *this;
   }
 
   OutputBuffer &operator<<(StringView R) { return (*this += R); }
 
+  OutputBuffer prepend(StringView R) {
+    size_t Size = R.size();
+
+    grow(Size);
+    std::memmove(Buffer + Size, Buffer, CurrentPosition);
+    std::memcpy(Buffer, R.begin(), Size);
+    CurrentPosition += Size;
+
+    return *this;
+  }
+
   OutputBuffer &operator<<(char C) { return (*this += C); }
 
   OutputBuffer &operator<<(long long N) {
     if (N < 0)
       writeUnsigned(static_cast<unsigned long long>(-N), true);
     else
       writeUnsigned(static_cast<unsigned long long>(N));
     return *this;

llvm/include/llvm/Demangle/Utility.h

public:
   OutputBuffer &operator+=(char C) {
     grow(1);
     Buffer[CurrentPosition++] = C;
     return *this;
   }
 
   OutputBuffer &operator<<(StringView R) { return (*this += R); }
 
+  OutputBuffer prepend(StringView R) {
+    size_t Size = R.size();
+
+    grow(Size);
+    std::memmove(Buffer + Size, Buffer, CurrentPosition);
+    std::memcpy(Buffer, R.begin(), Size);
+    CurrentPosition += Size;
+
+    return *this;
+  }
+
   OutputBuffer &operator<<(char C) { return (*this += C); }
 
   OutputBuffer &operator<<(long long N) {
     if (N < 0)
       writeUnsigned(static_cast<unsigned long long>(-N), true);
     else
       writeUnsigned(static_cast<unsigned long long>(N));
     return *this;

llvm/unittests/Demangle/OutputBufferTest.cpp

TEST(OutputBufferTest, Insert) {
   OB.insert(5, "y", 1);
   EXPECT_EQ("xabcdy", toString(OB));
 
   OB.insert(3, "defghi", 6);
   EXPECT_EQ("xabdefghicdy", toString(OB));
 
   std::free(OB.getBuffer());
 }
+
+TEST(OutputBufferTest, Prepend) {
+  OutputBuffer OB;
+
+  OB.prepend("n");
+  EXPECT_EQ("n", toString(OB));
+
+  OB << "abc";
+  OB.prepend("def");
+  EXPECT_EQ("defnabc", toString(OB));
+
+  OB.setCurrentPosition(3);
+
+  OB.prepend("abc");
+  EXPECT_EQ("abcdef", toString(OB));
+
+  std::free(OB.getBuffer());
+}