[LangRef] update according to unwinding support in inline asm

https://reviews.llvm.org/D95745 introduced a new `unwind` keyword for inline assembler expressions. Inline asms marked with the `unwind` keyword allows stack unwinding from inline assembly because the compiler emits unwinding information ("around" the inline asm) as it would for calls/invokes. Unwinding the stack from within non-unwind inline asm may cause UB.

Reviewed By: Amanieu

Differential Revision: https://reviews.llvm.org/D102642

diff --git a/llvm/docs/LangRef.rst b/llvm/docs/LangRef.rst
index 6d6c72c..0dc0b53 100644 (file)
--- a/llvm/docs/LangRef.rst
+++ b/llvm/docs/LangRef.rst
@@ -4303,9 +4303,20 @@ the only supported dialects. An example is:
 
     call void asm inteldialect "eieio", ""()
 
-If multiple keywords appear the '``sideeffect``' keyword must come
-first, the '``alignstack``' keyword second and the '``inteldialect``'
-keyword last.
+In the case that the inline asm might unwind the stack,
+the '``unwind``' keyword must be used, so that the compiler emits
+unwinding information:
+
+.. code-block:: llvm
+
+    call void asm unwind "call func", ""()
+
+If the inline asm unwinds the stack and isn't marked with
+the '``unwind``' keyword, the behavior is undefined.
+
+If multiple keywords appear, the '``sideeffect``' keyword must come
+first, the '``alignstack``' keyword second, the '``inteldialect``' keyword
+third and the '``unwind``' keyword last.
 
 Inline Asm Constraint String
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^