[TargetLowering] Correctly track NumFixedArgs field of CallLoweringInfo

The NumFixedArgs field of CallLoweringInfo is used by
TargetLowering::LowerCallTo to determine whether a given argument is passed
using the vararg calling convention or not (specifically, to set IsFixed for
each ISD::OutputArg).

Firstly, CallLoweringInfo::setLibCallee and CallLoweringInfo::setCallee both
incorrectly set NumFixedArgs based on the _previous_ args list. Secondly,
TargetLowering::LowerCallTo failed to increment NumFixedArgs when modifying
the argument list so a pointer is passed for the return value.

If your backend uses the IsFixed property or directly accesses NumFixedArgs, 
it is _possible_ this change could result in codegen changes (although the 
previous behaviour would have been incorrect). No such cases have been
identified during code review for any in-tree architecture.

Differential Revision: https://reviews.llvm.org/D37898

llvm-svn: 315457

1 files changed, 1 insertions, 0 deletions

diff --git a/llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp b/llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
index df49b0474f3..75641e05648 100644
--- a/llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
@@ -8077,6 +8077,7 @@ TargetLowering::LowerCallTo(TargetLowering::CallLoweringInfo &CLI) const {
     Entry.IsSwiftError = false;
     Entry.Alignment = Align;
     CLI.getArgs().insert(CLI.getArgs().begin(), Entry);
+    CLI.NumFixedArgs += 1;
     CLI.RetTy = Type::getVoidTy(CLI.RetTy->getContext());
 
     // sret demotion isn't compatible with tail-calls, since the sret argument