From c2e0d7f1eb25bd9b4a8eaa7990cd0fd3a8c416bb Mon Sep 17 00:00:00 2001 From: Josh Stone Date: Wed, 3 Apr 2019 15:44:49 -0700 Subject: Never return uninhabited values at all Functions with uninhabited return values are already marked `noreturn`, but we were still generating return instructions for this. When running with `-C passes=lint`, LLVM prints: Unusual: Return statement in function with noreturn attribute The LLVM manual makes a stronger statement about `noreturn` though: > This produces undefined behavior at runtime if the function ever does dynamically return. We now emit an `abort` anywhere that would have tried to return an uninhabited value. --- src/librustc_codegen_ssa/mir/block.rs | 7 +++++++ 1 file changed, 7 insertions(+) (limited to 'src/librustc_codegen_ssa') diff --git a/src/librustc_codegen_ssa/mir/block.rs b/src/librustc_codegen_ssa/mir/block.rs index 53e8f7ed88b..aaa0be20412 100644 --- a/src/librustc_codegen_ssa/mir/block.rs +++ b/src/librustc_codegen_ssa/mir/block.rs @@ -238,6 +238,13 @@ impl<'a, 'tcx: 'a, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> { } } } + if self.fn_ty.ret.layout.abi.is_uninhabited() { + // Functions with uninhabited return values are marked `noreturn`, + // so we should make sure that we never actually do. + bx.abort(); + bx.unreachable(); + return; + } let llval = match self.fn_ty.ret.mode { PassMode::Ignore(IgnoreMode::Zst) | PassMode::Indirect(..) => { bx.ret_void(); -- cgit 1.4.1-3-g733a5