Add ISD::EH_DWARF_CFA, simplify @llvm.eh.dwarf.cfa on Mips, fix on PowerPC

LLVM has an @llvm.eh.dwarf.cfa intrinsic, used to lower the GCC-compatible
__builtin_dwarf_cfa() builtin. As pointed out in PR26761, this is currently
broken on PowerPC (and likely on ARM as well). Currently, @llvm.eh.dwarf.cfa is
lowered using:

  ADD(FRAMEADDR, FRAME_TO_ARGS_OFFSET)

where FRAME_TO_ARGS_OFFSET defaults to the constant zero. On x86,
FRAME_TO_ARGS_OFFSET is lowered to 2*SlotSize. This setup, however, does not
work for PowerPC. Because of the way that the stack layout works, the canonical
frame address is not exactly (FRAMEADDR + FRAME_TO_ARGS_OFFSET) on PowerPC
(there is a lower save-area offset as well), so it is not just a matter of
implementing FRAME_TO_ARGS_OFFSET for PowerPC (unless we redefine its
semantics -- We can do that, since it is currently used only for
@llvm.eh.dwarf.cfa lowering, but the better to directly lower the CFA construct
itself (since it can be easily represented as a fixed-offset FrameIndex)). Mips
currently does this, but by using a custom lowering for ADD that specifically
recognizes the (FRAMEADDR, FRAME_TO_ARGS_OFFSET) pattern.

This change introduces a ISD::EH_DWARF_CFA node, which by default expands using
the existing logic, but can be directly lowered by the target. Mips is updated
to use this method (which simplifies its implementation, and I suspect makes it
more robust), and updates PowerPC to do the same.

Fixes PR26761.

Differential Revision: https://reviews.llvm.org/D24038

llvm-svn: 280350

1 files changed, 16 insertions, 0 deletions

diff --git a/llvm/lib/CodeGen/SelectionDAG/LegalizeDAG.cpp b/llvm/lib/CodeGen/SelectionDAG/LegalizeDAG.cpp
index 16365c0e808..71e9197b41c 100644
--- a/llvm/lib/CodeGen/SelectionDAG/LegalizeDAG.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/LegalizeDAG.cpp
@@ -1005,6 +1005,7 @@ void SelectionDAGLegalize::LegalizeOp(SDNode *Node) {
   case ISD::MERGE_VALUES:
   case ISD::EH_RETURN:
   case ISD::FRAME_TO_ARGS_OFFSET:
+  case ISD::EH_DWARF_CFA:
   case ISD::EH_SJLJ_SETJMP:
   case ISD::EH_SJLJ_LONGJMP:
   case ISD::EH_SJLJ_SETUP_DISPATCH:
@@ -2782,6 +2783,21 @@ bool SelectionDAGLegalize::ExpandNode(SDNode *Node) {
   case ISD::FRAME_TO_ARGS_OFFSET:
     Results.push_back(DAG.getConstant(0, dl, Node->getValueType(0)));
     break;
+  case ISD::EH_DWARF_CFA: {
+    SDValue CfaArg = DAG.getSExtOrTrunc(Node->getOperand(0), dl,
+                                        TLI.getPointerTy(DAG.getDataLayout()));
+    SDValue Offset = DAG.getNode(ISD::ADD, dl,
+                                 CfaArg.getValueType(),
+                                 DAG.getNode(ISD::FRAME_TO_ARGS_OFFSET, dl,
+                                             CfaArg.getValueType()),
+                                 CfaArg);
+    SDValue FA = DAG.getNode(
+        ISD::FRAMEADDR, dl, TLI.getPointerTy(DAG.getDataLayout()),
+        DAG.getConstant(0, dl, TLI.getPointerTy(DAG.getDataLayout())));
+    Results.push_back(DAG.getNode(ISD::ADD, dl, FA.getValueType(),
+                                  FA, Offset));
+    break;
+  }
   case ISD::FLT_ROUNDS_:
     Results.push_back(DAG.getConstant(1, dl, Node->getValueType(0)));
     break;