From 842b1bdd940e365898581d6ff54794b8fa1a13c9 Mon Sep 17 00:00:00 2001 From: Jim Grosbach Date: Tue, 9 Jul 2013 02:07:28 +0000 Subject: [PATCH] X86: Add comment. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@185900 91177308-0d34-0410-b5e6-96231b3b80d8 --- lib/Target/X86/X86ISelDAGToDAG.cpp | 5 +++++ 1 file changed, 5 insertions(+) diff --git a/lib/Target/X86/X86ISelDAGToDAG.cpp b/lib/Target/X86/X86ISelDAGToDAG.cpp index b07928150f3..9465420ba90 100644 --- a/lib/Target/X86/X86ISelDAGToDAG.cpp +++ b/lib/Target/X86/X86ISelDAGToDAG.cpp @@ -2531,6 +2531,11 @@ SDNode *X86DAGToDAGISel::Select(SDNode *Node) { // Prevent use of AH in a REX instruction by referencing AX instead. // Shift it down 8 bits. + // + // The current assumption of the register allocator is that isel + // won't generate explicit references to the GPR8_NOREX registers. If + // the allocator and/or the backend get enhanced to be more robust in + // that regard, this can be, and should be, removed. if (HiReg == X86::AH && Subtarget->is64Bit() && !SDValue(Node, 1).use_empty()) { SDValue Result = CurDAG->getCopyFromReg(CurDAG->getEntryNode(), dl, -- 2.34.1