Revert "[clang][CodeGen] Zero init unspecified fields in initializers in C" (#109898)

Reverts llvm/llvm-project#97121

Causing failures on LNT bots; log shows a crash in
ConstStructBuilder::BuildStruct.

1 files changed, 0 insertions, 51 deletions

diff --git a/clang/lib/CodeGen/CodeGenModule.h b/clang/lib/CodeGen/CodeGenModule.h
index fcdfef0..c58bb88 100644
--- a/clang/lib/CodeGen/CodeGenModule.h
+++ b/clang/lib/CodeGen/CodeGenModule.h
@@ -1676,57 +1676,6 @@ public:
     MustTailCallUndefinedGlobals.insert(Global);
   }
 
-  bool shouldZeroInitPadding() const {
-    // In C23 (N3096) $6.7.10:
-    // """
-    // If any object is initialized with an empty iniitializer, then it is
-    // subject to default initialization:
-    //  - if it is an aggregate, every member is initialized (recursively)
-    //  according to these rules, and any padding is initialized to zero bits;
-    //  - if it is a union, the first named member is initialized (recursively)
-    //  according to these rules, and any padding is initialized to zero bits.
-    //
-    // If the aggregate or union contains elements or members that are
-    // aggregates or unions, these rules apply recursively to the subaggregates
-    // or contained unions.
-    //
-    // If there are fewer initializers in a brace-enclosed list than there are
-    // elements or members of an aggregate, or fewer characters in a string
-    // literal used to initialize an array of known size than there are elements
-    // in the array, the remainder of the aggregate is subject to default
-    // initialization.
-    // """
-    //
-    // From my understanding, the standard is ambiguous in the following two
-    // areas:
-    // 1. For a union type with empty initializer, if the first named member is
-    // not the largest member, then the bytes comes after the first named member
-    // but before padding are left unspecified. An example is:
-    //    union U { int a; long long b;};
-    //    union U u = {};  // The first 4 bytes are 0, but 4-8 bytes are left
-    //    unspecified.
-    //
-    // 2. It only mentions padding for empty initializer, but doesn't mention
-    // padding for a non empty initialization list. And if the aggregation or
-    // union contains elements or members that are aggregates or unions, and
-    // some are non empty initializers, while others are empty initiailizers,
-    // the padding initialization is unclear. An example is:
-    //    struct S1 { int a; long long b; };
-    //    struct S2 { char c; struct S1 s1; };
-    //    // The values for paddings between s2.c and s2.s1.a, between s2.s1.a
-    //    and s2.s1.b are unclear.
-    //    struct S2 s2 = { 'c' };
-    //
-    // Here we choose to zero initiailize left bytes of a union type. Because
-    // projects like the Linux kernel are relying on this behavior. If we don't
-    // explicitly zero initialize them, the undef values can be optimized to
-    // return gabage data. We also choose to zero initialize paddings for
-    // aggregates and unions, no matter they are initialized by empty
-    // initializers or non empty initializers. This can provide a consistent
-    // behavior. So projects like the Linux kernel can rely on it.
-    return !getLangOpts().CPlusPlus;
-  }
-
 private:
   bool shouldDropDLLAttribute(const Decl *D, const llvm::GlobalValue *GV) const;