From 41d6ab4b884120123e4f03bf284166f3af73deaa Mon Sep 17 00:00:00 2001 From: Dan Gohman Date: Tue, 24 Aug 2010 14:31:06 +0000 Subject: [PATCH] Add a comment explaining why this code is more complex than it initially seems it should require. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@111913 91177308-0d34-0410-b5e6-96231b3b80d8 --- lib/AsmParser/LLParser.h | 8 ++++++++ 1 file changed, 8 insertions(+) diff --git a/lib/AsmParser/LLParser.h b/lib/AsmParser/LLParser.h index 444bae2390e..5ac7337b136 100644 --- a/lib/AsmParser/LLParser.h +++ b/lib/AsmParser/LLParser.h @@ -80,6 +80,14 @@ namespace llvm { // Instruction metadata resolution. Each instruction can have a list of // MDRef info associated with them. + // + // The simpler approach of just creating temporary MDNodes and then calling + // RAUW on them when the definition is processed doesn't work because some + // instruction metadata kinds, such as dbg, get stored in the IR in an + // "optimized" format which doesn't participate in the normal value use + // lists. This means that RAUW doesn't work, even on temporary MDNodes + // which otherwise support RAUW. Instead, we defer resolving MDNode + // references until the definitions have been processed. struct MDRef { SMLoc Loc; unsigned MDKind, MDSlot;