Fix stack-buffer-overflow in generated code

When generating code for a local, we were using the LLVM type
for the allocation. However, we were assuming that the allocation
was sized according to the julia datatype size. These two sizes
do not match, as the julia size is rounded up to alignment,
causing a stack buffer overflow.

src/codegen.cpp

@@ -4341,7 +4341,7 @@ static jl_cgval_t emit_varinfo(jl_codectx_t &ctx, jl_varinfo_t &vi, jl_sym_t *va
         }
         else {
             // copy value to a non-mutable (non-volatile SSA) location
-            AllocaInst *varslot = cast<AllocaInst>(vi.value.V);
+            AllocaInst *varslot = cast<AllocaInst>(vi.value.V->stripPointerCasts());
             Type *T = varslot->getAllocatedType();
             assert(!varslot->isArrayAllocation() && "variables not expected to be VLA");
             AllocaInst *ssaslot = cast<AllocaInst>(varslot->clone());
@@ -7055,7 +7055,12 @@ static jl_llvm_functions_t
             Type *vtype = julia_type_to_llvm(ctx, jt, &isboxed);
             assert(!isboxed);
             assert(!type_is_ghost(vtype) && "constants should already be handled");
-            Value *lv = new AllocaInst(vtype, M->getDataLayout().getAllocaAddrSpace(), jl_symbol_name(s), /*InsertBefore*/ctx.topalloca);
+            Type *alloc_type = ArrayType::get(getInt8Ty(ctx.builder.getContext()), jl_datatype_size(jt));
+            Value *lv = new AllocaInst(alloc_type, M->getDataLayout().getAllocaAddrSpace(), nullptr,
+                Align(jl_datatype_align(jt)), jl_symbol_name(s), /*InsertBefore*/ctx.topalloca);
+#ifndef JL_LLVM_OPAQUE_POINTERS
+            lv = new BitCastInst(lv, PointerType::get(vtype, M->getDataLayout().getAllocaAddrSpace()), "", /*InsertBefore*/ctx.topalloca);
+#endif
             if (CountTrackedPointers(vtype).count) {
                 StoreInst *SI = new StoreInst(Constant::getNullValue(vtype), lv, false, Align(sizeof(void*)));
                 SI->insertAfter(ctx.topalloca);