Variable auto-init: fix __block initialization

Summary:
Automatic initialization [1] of __block variables was trampling over the block's
headers after they'd been initialized, which caused self-init usage to crash,
such as here:

  typedef struct XYZ { void (^block)(); } *xyz_t;
  __attribute__((noinline))
  xyz_t create(void (^block)()) {
    xyz_t myself = malloc(sizeof(struct XYZ));
    myself->block = block;
    return myself;
  }
  int main() {
    __block xyz_t captured = create(^(){ (void)captured; });
  }

This type of code shouldn't be broken by variable auto-init, even if it's
sketchy.

[1] With -ftrivial-auto-var-init=pattern

<rdar://problem/47798396>

Reviewers: rjmccall, pcc, kcc

Subscribers: jkorous, dexonsmith, cfe-commits

Tags: #clang

Differential Revision: https://reviews.llvm.org/D57797

llvm-svn: 353495

1 files changed, 7 insertions, 3 deletions

diff --git a/clang/lib/CodeGen/CGDecl.cpp b/clang/lib/CodeGen/CGDecl.cpp
index f91fb010a79..734aa7e2c33 100644
--- a/clang/lib/CodeGen/CGDecl.cpp
+++ b/clang/lib/CodeGen/CGDecl.cpp
@@ -1633,11 +1633,15 @@ void CodeGenFunction::EmitAutoVarInit(const AutoVarEmission &emission) {
                   ? LangOptions::TrivialAutoVarInitKind::Uninitialized
                   : getContext().getLangOpts().getTrivialAutoVarInit()));
 
-  auto initializeWhatIsTechnicallyUninitialized = [&]() {
+  auto initializeWhatIsTechnicallyUninitialized = [&](Address Loc) {
     if (trivialAutoVarInit ==
         LangOptions::TrivialAutoVarInitKind::Uninitialized)
       return;
 
+    // Only initialize a __block's storage: we always initialize the header.
+    if (emission.IsEscapingByRef)
+      Loc = emitBlockByrefAddress(Loc, &D, /*follow=*/false);
+
     CharUnits Size = getContext().getTypeSizeInChars(type);
     if (!Size.isZero()) {
       switch (trivialAutoVarInit) {
@@ -1714,7 +1718,7 @@ void CodeGenFunction::EmitAutoVarInit(const AutoVarEmission &emission) {
   };
 
   if (isTrivialInitializer(Init)) {
-    initializeWhatIsTechnicallyUninitialized();
+    initializeWhatIsTechnicallyUninitialized(Loc);
     return;
   }
 
@@ -1728,7 +1732,7 @@ void CodeGenFunction::EmitAutoVarInit(const AutoVarEmission &emission) {
   }
 
   if (!constant) {
-    initializeWhatIsTechnicallyUninitialized();
+    initializeWhatIsTechnicallyUninitialized(Loc);
     LValue lv = MakeAddrLValue(Loc, type);
     lv.setNonGC(true);
     return EmitExprAsInit(Init, &D, lv, capturedByInit);