[CodeGen] Don't emit lifetime intrinsics for some local variables

Summary:
Current generation of lifetime intrinsics does not handle cases like:

```
  {
    char x;
  l1:
    bar(&x, 1);
  }
  goto l1;

```
We will get code like this:

```
  %x = alloca i8, align 1
  call void @llvm.lifetime.start(i64 1, i8* nonnull %x)
  br label %l1
l1:
  %call = call i32 @bar(i8* nonnull %x, i32 1)
  call void @llvm.lifetime.end(i64 1, i8* nonnull %x)
  br label %l1
```

So the second time bar was called for x which is marked as dead.
Lifetime markers here are misleading so it's better to remove them at all.
This type of bypasses are rare, e.g. code detects just 8 functions building
clang (2329 targets).

PR28267

Reviewers: eugenis

Subscribers: beanz, mgorny, cfe-commits

Differential Revision: https://reviews.llvm.org/D24693

llvm-svn: 285176

1 files changed, 5 insertions, 0 deletions

diff --git a/clang/lib/CodeGen/CodeGenFunction.h b/clang/lib/CodeGen/CodeGenFunction.h
index 123c04027ef..7a6fd93052b 100644
--- a/clang/lib/CodeGen/CodeGenFunction.h
+++ b/clang/lib/CodeGen/CodeGenFunction.h
@@ -21,6 +21,7 @@
 #include "CodeGenModule.h"
 #include "CodeGenPGO.h"
 #include "EHScopeStack.h"
+#include "VarBypassDetector.h"
 #include "clang/AST/CharUnits.h"
 #include "clang/AST/ExprCXX.h"
 #include "clang/AST/ExprObjC.h"
@@ -141,6 +142,10 @@ public:
   LoopInfoStack LoopStack;
   CGBuilderTy Builder;
 
+  // Stores variables for which we can't generate correct lifetime markers
+  // because of jumps.
+  VarBypassDetector Bypasses;
+
   /// \brief CGBuilder insert helper. This function is called after an
   /// instruction is created using Builder.
   void InsertHelper(llvm::Instruction *I, const llvm::Twine &Name,