[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, 8 insertions, 1 deletions

diff --git a/clang/lib/CodeGen/CodeGenFunction.cpp b/clang/lib/CodeGen/CodeGenFunction.cpp
index a4ea7b608e6..538b50d56d4 100644
--- a/clang/lib/CodeGen/CodeGenFunction.cpp
+++ b/clang/lib/CodeGen/CodeGenFunction.cpp
@@ -1066,6 +1066,13 @@ void CodeGenFunction::GenerateCode(GlobalDecl GD, llvm::Function *Fn,
     if (SpecDecl->hasBody(SpecDecl))
       Loc = SpecDecl->getLocation();
 
+  Stmt *Body = FD->getBody();
+
+  // Initialize helper which will detect jumps which can cause invalid lifetime
+  // markers.
+  if (Body && ShouldEmitLifetimeMarkers)
+    Bypasses.Init(Body);
+
   // Emit the standard function prologue.
   StartFunction(GD, ResTy, Fn, FnInfo, Args, Loc, BodyRange.getBegin());
 
@@ -1095,7 +1102,7 @@ void CodeGenFunction::GenerateCode(GlobalDecl GD, llvm::Function *Fn,
     // Implicit copy-assignment gets the same special treatment as implicit
     // copy-constructors.
     emitImplicitAssignmentOperatorBody(Args);
-  } else if (Stmt *Body = FD->getBody()) {
+  } else if (Body) {
     EmitFunctionBody(Args, Body);
   } else
     llvm_unreachable("no definition for emitted function");