From f79c5e2f842e952d26a2aa380fa71d5917c865a0 Mon Sep 17 00:00:00 2001 From: Jakob Stoklund Olesen Date: Thu, 31 Jan 2013 17:56:23 +0000 Subject: Clarify intent. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@174068 91177308-0d34-0410-b5e6-96231b3b80d8 --- utils/TableGen/CodeGenRegisters.cpp | 6 ++++++ 1 file changed, 6 insertions(+) (limited to 'utils/TableGen/CodeGenRegisters.cpp') diff --git a/utils/TableGen/CodeGenRegisters.cpp b/utils/TableGen/CodeGenRegisters.cpp index e902ce031f..4238340ff0 100644 --- a/utils/TableGen/CodeGenRegisters.cpp +++ b/utils/TableGen/CodeGenRegisters.cpp @@ -1198,6 +1198,12 @@ void CodeGenRegBank::computeSubRegIndexLaneMasks() { if (Idx->getComposites().empty()) { Idx->LaneMask = 1u << Bit; // Share bit 31 in the unlikely case there are more than 32 leafs. + // + // Sharing bits is harmless; it allows graceful degradation in targets + // with more than 32 vector lanes. They simply get a limited resolution + // view of lanes beyond the 32nd. + // + // See also the comment for getSubRegIndexLaneMask(). if (Bit < 31) ++Bit; } else { Idx->LaneMask = 0; -- cgit v1.2.3