[Macros] Replace use of free for Swift-allocated pointer

We cannot depend on Swift's unsafe pointers using `malloc` under the
hood, so don't use `free` on them. Instead, expose entry points from
Swift to C++ to free any Swift-allocated data structures that need to
be deallocated from C++.

Author: DougGregor

lib/ASTGen/Sources/ASTGen/Macros.swift

@@ -170,6 +170,11 @@ func allocateUTF8String(
   }
 }
 
+@_cdecl("swift_ASTGen_freeString")
+public func freeString(pointer: UnsafePointer<UInt8>?) {
+  pointer?.deallocate()
+}
+
 /// Diagnostics produced here.
 enum ASTGenMacroDiagnostic: DiagnosticMessage, FixItMessage {
   case thrownError(Error)
@@ -413,6 +418,14 @@ func checkMacroDefinition(
   }
 }
 
+@_cdecl("swift_ASTGen_freeExpansionReplacements")
+public func freeExpansionReplacements(
+  pointer: UnsafeMutablePointer<Int>?,
+  numReplacements: Int
+) {
+  UnsafeMutableBufferPointer(start: pointer, count: numReplacements).deallocate()
+}
+
 // Make an expansion result for '@_cdecl' function caller.
 func makeExpansionOutputResult(
   expandedSource: String?,

lib/Sema/TypeCheckMacros.cpp

@@ -49,6 +49,8 @@ using namespace swift;
 extern "C" void *swift_ASTGen_resolveMacroType(const void *macroType);
 extern "C" void swift_ASTGen_destroyMacro(void *macro);
 
+extern "C" void swift_ASTGen_freeString(const char *str);
+
 extern "C" void *swift_ASTGen_resolveExecutableMacro(
     const char *moduleName, ptrdiff_t moduleNameLength,
     const char *typeName, ptrdiff_t typeNameLength,
@@ -64,6 +66,9 @@ extern "C" ptrdiff_t swift_ASTGen_checkMacroDefinition(
     ptrdiff_t **replacementsPtr,
     ptrdiff_t *numReplacements
 );
+extern "C" void swift_ASTGen_freeExpansionReplacements(
+    ptrdiff_t *replacementsPtr,
+    ptrdiff_t numReplacements);
 
 extern "C" ptrdiff_t swift_ASTGen_expandFreestandingMacro(
     void *diagEngine, void *macro, uint8_t externalKind,
@@ -197,8 +202,8 @@ MacroDefinition MacroDefinitionRequest::evaluate(
 
   // Clean up after the call.
   SWIFT_DEFER {
-    free(externalMacroNamePtr);
-    free(replacements);
+    swift_ASTGen_freeString(externalMacroNamePtr);
+    swift_ASTGen_freeExpansionReplacements(replacements, numReplacements);
   };
 
   if (checkResult < 0 && ctx.CompletionCallback) {
@@ -1065,7 +1070,7 @@ evaluateFreestandingMacro(FreestandingMacroExpansion *expansion,
     evaluatedSource = llvm::MemoryBuffer::getMemBufferCopy(
         {evaluatedSourceAddress, (size_t)evaluatedSourceLength},
         adjustMacroExpansionBufferName(*discriminator));
-    free((void *)evaluatedSourceAddress);
+    swift_ASTGen_freeString(evaluatedSourceAddress);
     break;
 #else
     ctx.Diags.diagnose(loc, diag::macro_unsupported);
@@ -1343,7 +1348,7 @@ static SourceFile *evaluateAttachedMacro(MacroDecl *macro, Decl *attachedTo,
     evaluatedSource = llvm::MemoryBuffer::getMemBufferCopy(
         {evaluatedSourceAddress, (size_t)evaluatedSourceLength},
         adjustMacroExpansionBufferName(*discriminator));
-    free((void *)evaluatedSourceAddress);
+    swift_ASTGen_freeString(evaluatedSourceAddress);
     break;
 #else
     attachedTo->diagnose(diag::macro_unsupported);