[clang] Add support for `__declspec(no_init_all)` (#116847)

In MSVC, when `/d1initall` is enabled, `__declspec(no_init_all)` can be
applied to a type to suppress auto-initialization for all instances of
that type or to a function to suppress auto-initialization for all
locals within that function.

This change does the same for Clang, except that it applies to the
`-ftrivial-auto-var-init` flag instead.

NOTE: I did not add a Clang-specific spelling for this but would be
happy to make a followup PR if folks are interested in that.

1 files changed, 12 insertions, 10 deletions

diff --git a/clang/lib/CodeGen/CGDecl.cpp b/clang/lib/CodeGen/CGDecl.cpp
index 6e9d28c..47b21bc 100644
--- a/clang/lib/CodeGen/CGDecl.cpp
+++ b/clang/lib/CodeGen/CGDecl.cpp
@@ -1899,13 +1899,16 @@ void CodeGenFunction::EmitAutoVarInit(const AutoVarEmission &emission) {
   const Address Loc =
       locIsByrefHeader ? emission.getObjectAddress(*this) : emission.Addr;
 
+  auto hasNoTrivialAutoVarInitAttr = [&](const Decl *D) {
+    return D && D->hasAttr<NoTrivialAutoVarInitAttr>();
+  };
   // Note: constexpr already initializes everything correctly.
   LangOptions::TrivialAutoVarInitKind trivialAutoVarInit =
-      (D.isConstexpr()
+      ((D.isConstexpr() || D.getAttr<UninitializedAttr>() ||
+        hasNoTrivialAutoVarInitAttr(type->getAsTagDecl()) ||
+        hasNoTrivialAutoVarInitAttr(CurFuncDecl))
            ? LangOptions::TrivialAutoVarInitKind::Uninitialized
-           : (D.getAttr<UninitializedAttr>()
-                  ? LangOptions::TrivialAutoVarInitKind::Uninitialized
-                  : getContext().getLangOpts().getTrivialAutoVarInit()));
+           : getContext().getLangOpts().getTrivialAutoVarInit());
 
   auto initializeWhatIsTechnicallyUninitialized = [&](Address Loc) {
     if (trivialAutoVarInit ==
@@ -1944,13 +1947,13 @@ void CodeGenFunction::EmitAutoVarInit(const AutoVarEmission &emission) {
                                   replaceUndef(CGM, isPattern, constant));
     }
 
-    if (constant && D.getType()->isBitIntType() &&
-        CGM.getTypes().typeRequiresSplitIntoByteArray(D.getType())) {
+    if (constant && type->isBitIntType() &&
+        CGM.getTypes().typeRequiresSplitIntoByteArray(type)) {
       // Constants for long _BitInt types are split into individual bytes.
       // Try to fold these back into an integer constant so it can be stored
       // properly.
-      llvm::Type *LoadType = CGM.getTypes().convertTypeForLoadStore(
-          D.getType(), constant->getType());
+      llvm::Type *LoadType =
+          CGM.getTypes().convertTypeForLoadStore(type, constant->getType());
       constant = llvm::ConstantFoldLoadFromConst(
           constant, LoadType, llvm::APInt::getZero(32), CGM.getDataLayout());
     }
@@ -1967,8 +1970,7 @@ void CodeGenFunction::EmitAutoVarInit(const AutoVarEmission &emission) {
       // It may be that the Init expression uses other uninitialized memory,
       // but auto-var-init here would not help, as auto-init would get
       // overwritten by Init.
-      if (!D.getType()->isScalarType() || capturedByInit ||
-          isAccessedBy(D, Init)) {
+      if (!type->isScalarType() || capturedByInit || isAccessedBy(D, Init)) {
         initializeWhatIsTechnicallyUninitialized(Loc);
       }
     }