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Fix read_volatile intrinsic #223

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37 changes: 28 additions & 9 deletions crates/rustc_codegen_nvvm/src/intrinsic.rs
Original file line number Diff line number Diff line change
Expand Up @@ -295,22 +295,41 @@ impl<'ll, 'tcx> IntrinsicCallBuilderMethods<'tcx> for Builder<'_, 'll, 'tcx> {
}
}
sym::volatile_load | sym::unaligned_volatile_load => {
let tp_ty = fn_args.type_at(0);
let mut ptr = args[0].immediate();
if let PassMode::Cast { cast: ty, .. } = &fn_abi.ret.mode {
ptr = self.pointercast(ptr, self.type_ptr_to(ty.llvm_type(self)));
}
let load = self.volatile_load(self.type_i1(), ptr);
// The `*const T` or `*mut T` operand.
let ptr_operand = &args[0];
let src_ptr_llval = ptr_operand.immediate();

// Determine the type T (the pointee type) and its LLVM representation.
// `ptr_operand.layout.ty` is the Rust type `*const T` (or `*mut T`). We
// need the layout of `T`.
let pointee_rust_ty =
ptr_operand
.layout
.ty
.builtin_deref(true)
.unwrap_or_else(|| {
span_bug!(span, "volatile_load input pointer is not a pointer type")
});
let layout_of_pointee = self.layout_of(pointee_rust_ty);
let llvm_ty_of_pointee = layout_of_pointee.llvm_type(self);

// Call volatile_load with the correct LLVM type of T. The
// `volatile_load` does a pointercast so we do not need to do it here.
let loaded_llval = self.volatile_load(llvm_ty_of_pointee, src_ptr_llval);

// Set alignment for the LLVM load instruction based on the alignment of
// `T`.
let align = if name == sym::unaligned_volatile_load {
1
} else {
self.align_of(tp_ty).bytes() as u32
layout_of_pointee.align.abi.bytes() as u32
};
unsafe {
llvm::LLVMSetAlignment(load, align);
llvm::LLVMSetAlignment(loaded_llval, align);
}

if !result.layout.is_zst() {
self.store_to_place(load, result.val);
self.store_to_place(loaded_llval, result.val);
}
return Ok(());
}
Expand Down