From f71e0daa29b232d8f689f77fecb84dcb87fce6da Mon Sep 17 00:00:00 2001 From: Xiang Fan Date: Thu, 6 Jun 2019 08:39:20 +0800 Subject: Add llvm.sideeffect to potential infinite loops and recursions LLVM assumes that a thread will eventually cause side effect. This is not true in Rust if a loop or recursion does nothing in its body, causing undefined behavior even in common cases like `loop {}`. Inserting llvm.sideeffect fixes the undefined behavior. As a micro-optimization, only insert llvm.sideeffect when jumping back in blocks or calling a function. A patch for LLVM is expected to allow empty non-terminate code by default and fix this issue from LLVM side. https://github.com/rust-lang/rust/issues/28728 --- src/librustc_codegen_ssa/traits/intrinsic.rs | 1 + 1 file changed, 1 insertion(+) (limited to 'src/librustc_codegen_ssa/traits') diff --git a/src/librustc_codegen_ssa/traits/intrinsic.rs b/src/librustc_codegen_ssa/traits/intrinsic.rs index 7c79cd60210..2c484084c4a 100644 --- a/src/librustc_codegen_ssa/traits/intrinsic.rs +++ b/src/librustc_codegen_ssa/traits/intrinsic.rs @@ -20,6 +20,7 @@ pub trait IntrinsicCallMethods<'tcx>: BackendTypes { fn abort(&mut self); fn assume(&mut self, val: Self::Value); fn expect(&mut self, cond: Self::Value, expected: bool) -> Self::Value; + fn sideeffect(&mut self); /// Trait method used to inject `va_start` on the "spoofed" `VaListImpl` in /// Rust defined C-variadic functions. fn va_start(&mut self, val: Self::Value) -> Self::Value; -- cgit 1.4.1-3-g733a5