From 946317d07be338f25b554ab543308490a276b835 Mon Sep 17 00:00:00 2001 From: Andrew Trick Date: Thu, 31 Jan 2013 00:49:39 +0000 Subject: [PATCH] LangRef: Add a Rationale for volatile rules. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@174007 91177308-0d34-0410-b5e6-96231b3b80d8 --- docs/LangRef.rst | 10 ++++++++++ 1 file changed, 10 insertions(+) diff --git a/docs/LangRef.rst b/docs/LangRef.rst index ec34a31cd4c..0bcbe44bd4a 100644 --- a/docs/LangRef.rst +++ b/docs/LangRef.rst @@ -1085,6 +1085,16 @@ llvm.memcpy or llvm.memmove intrinsics even when those intrinsics are flagged volatile. Likewise, the backend should never split or merge target-legal volatile load/store instructions. +.. admonition:: Rationale + + Platforms may rely on volatile loads and stores of natively supported + data width to be executed as single instruction. For example, in C + this holds for an l-value of volatile primitive type with native + hardware support, but not necessarily for aggregate types. The + frontend upholds these expectations, which are intentionally + unspecified in the IR. The rules above ensure that IR transformation + do not violate the frontend's contract with the language. + .. _memmodel: Memory Model for Concurrent Operations -- 2.34.1