[demangler] Simplify OutputBuffer initialization

Every non-testcase use of OutputBuffer contains code to allocate an
initial buffer (using either 128 or 1024 as initial guesses). There's
now no need to do that, given recent changes to the buffer extension
heuristics -- it allocates a 1k(ish) buffer on first need.

Just pass in a buffer (if any) to the constructor.  Thus the
OutputBuffer's ownership of the buffer starts at its own lifetime
start. We can reduce the lifetime of this object in several cases.

That new constructor takes a 'size_t *' for the size argument, as all
uses with a non-null buffer are passing through a malloc'd buffer from
their own caller in this manner.

The buffer reset member function is never used, and is deleted.

The original buffer initialization code would return a failure code if
that first malloc failed.  Existing code either ignored that, called
std::terminate with a FIXME, or returned an error code.

But that's not foolproof anyway, as a subsequent buffer extension
failure ends up calling std::terminate. I am working on addressing
that unfortunate failure mode in a manner more consistent with the C++
ABI design.

Reviewed By: dblaikie

Differential Revision: https://reviews.llvm.org/D122604

1 files changed, 5 insertions, 16 deletions

diff --git a/llvm/lib/Demangle/ItaniumDemangle.cpp b/llvm/lib/Demangle/ItaniumDemangle.cpp
index 1c9209d..9b646ea 100644
--- a/llvm/lib/Demangle/ItaniumDemangle.cpp
+++ b/llvm/lib/Demangle/ItaniumDemangle.cpp
@@ -375,15 +375,12 @@ char *llvm::itaniumDemangle(const char *MangledName, char *Buf,
 
   int InternalStatus = demangle_success;
   Demangler Parser(MangledName, MangledName + std::strlen(MangledName));
-  OutputBuffer OB;
-
   Node *AST = Parser.parse();
 
   if (AST == nullptr)
     InternalStatus = demangle_invalid_mangled_name;
-  else if (!initializeOutputBuffer(Buf, N, OB, 1024))
-    InternalStatus = demangle_memory_alloc_failure;
   else {
+    OutputBuffer OB(Buf, N);
     assert(Parser.ForwardTemplateRefs.empty());
     AST->print(OB);
     OB += '\0';
@@ -427,9 +424,7 @@ bool ItaniumPartialDemangler::partialDemangle(const char *MangledName) {
 }
 
 static char *printNode(const Node *RootNode, char *Buf, size_t *N) {
-  OutputBuffer OB;
-  if (!initializeOutputBuffer(Buf, N, OB, 128))
-    return nullptr;
+  OutputBuffer OB(Buf, N);
   RootNode->print(OB);
   OB += '\0';
   if (N != nullptr)
@@ -472,9 +467,7 @@ char *ItaniumPartialDemangler::getFunctionDeclContextName(char *Buf,
     return nullptr;
   const Node *Name = static_cast<const FunctionEncoding *>(RootNode)->getName();
 
-  OutputBuffer OB;
-  if (!initializeOutputBuffer(Buf, N, OB, 128))
-    return nullptr;
+  OutputBuffer OB(Buf, N);
 
  KeepGoingLocalFunction:
   while (true) {
@@ -525,9 +518,7 @@ char *ItaniumPartialDemangler::getFunctionParameters(char *Buf,
     return nullptr;
   NodeArray Params = static_cast<FunctionEncoding *>(RootNode)->getParams();
 
-  OutputBuffer OB;
-  if (!initializeOutputBuffer(Buf, N, OB, 128))
-    return nullptr;
+  OutputBuffer OB(Buf, N);
 
   OB += '(';
   Params.printWithComma(OB);
@@ -543,9 +534,7 @@ char *ItaniumPartialDemangler::getFunctionReturnType(
   if (!isFunction())
     return nullptr;
 
-  OutputBuffer OB;
-  if (!initializeOutputBuffer(Buf, N, OB, 128))
-    return nullptr;
+  OutputBuffer OB(Buf, N);
 
   if (const Node *Ret =
           static_cast<const FunctionEncoding *>(RootNode)->getReturnType())