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.

llvm-svn: 345828

3 files changed, 15 insertions, 12 deletions

diff --git a/clang/lib/AST/ExprConstant.cpp b/clang/lib/AST/ExprConstant.cpp
index bf08d6bb657..9fc7b30b669 100644
--- a/clang/lib/AST/ExprConstant.cpp
+++ b/clang/lib/AST/ExprConstant.cpp
@@ -33,6 +33,7 @@
 //
 //===----------------------------------------------------------------------===//
 
+#include "clang/Analysis/Analyses/OSLog.h"
 #include "clang/AST/APValue.h"
 #include "clang/AST/ASTContext.h"
 #include "clang/AST/ASTDiagnostic.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: {
diff --git a/clang/lib/CodeGen/CGBuiltin.cpp b/clang/lib/CodeGen/CGBuiltin.cpp
index c67db26711a..271dc2a9662 100644
--- a/clang/lib/CodeGen/CGBuiltin.cpp
+++ b/clang/lib/CodeGen/CGBuiltin.cpp
@@ -3609,13 +3609,6 @@ RValue CodeGenFunction::EmitBuiltinExpr(const FunctionDecl *FD,
   case Builtin::BI__builtin_os_log_format:
     return emitBuiltinOSLogFormat(*E);
 
-  case Builtin::BI__builtin_os_log_format_buffer_size: {
-    analyze_os_log::OSLogBufferLayout Layout;
-    analyze_os_log::computeOSLogBufferLayout(CGM.getContext(), E, Layout);
-    return RValue::get(ConstantInt::get(ConvertType(E->getType()),
-                                        Layout.size().getQuantity()));
-  }
-
   case Builtin::BI__xray_customevent: {
     if (!ShouldXRayInstrumentFunction())
       return RValue::getIgnored();
diff --git a/clang/test/CodeGen/builtins.c b/clang/test/CodeGen/builtins.c
index 77b479e4c11..6ca3c414cf3 100644
--- a/clang/test/CodeGen/builtins.c
+++ b/clang/test/CodeGen/builtins.c
@@ -729,25 +729,28 @@ void test_builtin_os_log_merge_helper1(void *buf, unsigned u, long long ll) {
 
 // CHECK-LABEL: define void @test_builtin_os_log_errno
 void test_builtin_os_log_errno() {
-  // CHECK: %[[VLA:.*]] = alloca i8, i64 4, align 16
-  // CHECK: call void @__os_log_helper_16_2_1_0_96(i8* %[[VLA]])
+  // CHECK-NOT: @stacksave
+  // CHECK: %[[BUF:.*]] = alloca [4 x i8], align 1
+  // CHECK: %[[DECAY:.*]] = getelementptr inbounds [4 x i8], [4 x i8]* %[[BUF]], i32 0, i32 0
+  // CHECK: call void @__os_log_helper_1_2_1_0_96(i8* %[[DECAY]])
+  // CHECK-NOT: @stackrestore
 
   char buf[__builtin_os_log_format_buffer_size("%m")];
   __builtin_os_log_format(buf, "%m");
 }
 
-// CHECK-LABEL: define linkonce_odr hidden void @__os_log_helper_16_2_1_0_96
+// CHECK-LABEL: define linkonce_odr hidden void @__os_log_helper_1_2_1_0_96
 // CHECK: (i8* %[[BUFFER:.*]])
 
 // CHECK: %[[BUFFER_ADDR:.*]] = alloca i8*, align 8
 // CHECK: store i8* %[[BUFFER]], i8** %[[BUFFER_ADDR]], align 8
 // CHECK: %[[BUF:.*]] = load i8*, i8** %[[BUFFER_ADDR]], align 8
 // CHECK: %[[SUMMARY:.*]] = getelementptr i8, i8* %[[BUF]], i64 0
-// CHECK: store i8 2, i8* %[[SUMMARY]], align 16
+// CHECK: store i8 2, i8* %[[SUMMARY]], align 1
 // CHECK: %[[NUMARGS:.*]] = getelementptr i8, i8* %[[BUF]], i64 1
 // CHECK: store i8 1, i8* %[[NUMARGS]], align 1
 // CHECK: %[[ARGDESCRIPTOR:.*]] = getelementptr i8, i8* %[[BUF]], i64 2
-// CHECK: store i8 96, i8* %[[ARGDESCRIPTOR]], align 2
+// CHECK: store i8 96, i8* %[[ARGDESCRIPTOR]], align 1
 // CHECK: %[[ARGSIZE:.*]] = getelementptr i8, i8* %[[BUF]], i64 3
 // CHECK: store i8 0, i8* %[[ARGSIZE]], align 1
 // CHECK-NEXT: ret void