Reapply Logging: make os_log buffer size an integer constant expression.

The size of an os_log buffer is known at any stage of compilation, so making it
a constant expression means that the common idiom of declaring a buffer for it
won't result in a VLA. That allows the compiler to skip saving and restoring
the stack pointer around such buffers.

This also moves the OSLog helpers from libclangAnalysis to libclangAST
to avoid a circular dependency.

llvm-svn: 345866

1 files changed, 7 insertions, 0 deletions

diff --git a/clang/lib/AST/ExprConstant.cpp b/clang/lib/AST/ExprConstant.cpp
index 15efe433bd1..a85d5cf9d5f 100644
--- a/clang/lib/AST/ExprConstant.cpp
+++ b/clang/lib/AST/ExprConstant.cpp
@@ -39,6 +39,7 @@
 #include "clang/AST/ASTLambda.h"
 #include "clang/AST/CharUnits.h"
 #include "clang/AST/Expr.h"
+#include "clang/AST/OSLog.h"
 #include "clang/AST/RecordLayout.h"
 #include "clang/AST/StmtVisitor.h"
 #include "clang/AST/TypeLoc.h"
@@ -8126,6 +8127,12 @@ bool IntExprEvaluator::VisitBuiltinCallExpr(const CallExpr *E,
     llvm_unreachable("unexpected EvalMode");
   }
 
+  case Builtin::BI__builtin_os_log_format_buffer_size: {
+    analyze_os_log::OSLogBufferLayout Layout;
+    analyze_os_log::computeOSLogBufferLayout(Info.Ctx, E, Layout);
+    return Success(Layout.size().getQuantity(), E);
+  }
+
   case Builtin::BI__builtin_bswap16:
   case Builtin::BI__builtin_bswap32:
   case Builtin::BI__builtin_bswap64: {