[inlineasm] Propagate operand constraints to the backend

When SelectionDAGISel transforms a node representing an inline asm
block, memory constraint information is not preserved. This can cause
constraints to be broken when a memory offset is of the form:

offset + frame index

when the frame is resolved.

By propagating the constraints all the way to the backend, targets can
enforce memory operands of inline assembly to conform to their constraints.

For MIPSR6, some instructions had their offsets reduced to 9 bits from
16 bits such as ll/sc. This becomes problematic when using inline assembly
to perform atomic operations, as an offset can generated that is too big to
encode in the instruction.

Reviewers: dsanders, vkalintris

Differential Review: https://reviews.llvm.org/D21615

llvm-svn: 275786

1 files changed, 3 insertions, 3 deletions

diff --git a/llvm/lib/CodeGen/SelectionDAG/SelectionDAGISel.cpp b/llvm/lib/CodeGen/SelectionDAG/SelectionDAGISel.cpp
index a46d9aaa9d7..1d61657194c 100644
--- a/llvm/lib/CodeGen/SelectionDAG/SelectionDAGISel.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/SelectionDAGISel.cpp
@@ -1950,15 +1950,15 @@ void SelectionDAGISel::SelectInlineAsmMemoryOperands(std::vector<SDValue> &Ops,
 
       // Otherwise, this is a memory operand.  Ask the target to select it.
       std::vector<SDValue> SelOps;
-      if (SelectInlineAsmMemoryOperand(InOps[i+1],
-                                       InlineAsm::getMemoryConstraintID(Flags),
-                                       SelOps))
+      unsigned ConstraintID = InlineAsm::getMemoryConstraintID(Flags);
+      if (SelectInlineAsmMemoryOperand(InOps[i+1], ConstraintID, SelOps))
         report_fatal_error("Could not match memory address.  Inline asm"
                            " failure!");
 
       // Add this to the output node.
       unsigned NewFlags =
         InlineAsm::getFlagWord(InlineAsm::Kind_Mem, SelOps.size());
+      NewFlags = InlineAsm::getFlagWordForMem(NewFlags, ConstraintID);
       Ops.push_back(CurDAG->getTargetConstant(NewFlags, DL, MVT::i32));
       Ops.insert(Ops.end(), SelOps.begin(), SelOps.end());
       i += 2;