CodeGen: support SwiftError SwiftCC on Windows x64

Add support for passing SwiftError through a register on the Windows x64
calling convention.  This allows the use of swifterror attributes on
parameters which is used by the swift front end for the `Error`
parameter.  This partially enables building the swift standard library
for Windows x86_64.

llvm-svn: 313791

2 files changed, 5 insertions, 0 deletions

diff --git a/llvm/lib/CodeGen/SelectionDAG/SelectionDAGISel.cpp b/llvm/lib/CodeGen/SelectionDAG/SelectionDAGISel.cpp
index 9acaa446447..15d06871e70 100644
--- a/llvm/lib/CodeGen/SelectionDAG/SelectionDAGISel.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/SelectionDAGISel.cpp
@@ -1253,6 +1253,8 @@ static void propagateSwiftErrorVRegs(FunctionLoweringInfo *FuncInfo) {
       // If we don't need a phi create a copy to the upward exposed vreg.
       if (!needPHI) {
         assert(UpwardsUse);
+        assert(!VRegs.empty() &&
+               "No predecessors?  Is the Calling Convention correct?");
         unsigned DestReg = UUseVReg;
         BuildMI(*MBB, MBB->getFirstNonPHI(), DLoc, TII->get(TargetOpcode::COPY),
                 DestReg)
diff --git a/llvm/lib/Target/X86/X86CallingConv.td b/llvm/lib/Target/X86/X86CallingConv.td
index 26461986427..64c81391578 100644
--- a/llvm/lib/Target/X86/X86CallingConv.td
+++ b/llvm/lib/Target/X86/X86CallingConv.td
@@ -592,6 +592,9 @@ def CC_X86_Win64_C : CallingConv<[
   // The 'nest' parameter, if any, is passed in R10.
   CCIfNest<CCAssignToReg<[R10]>>,
 
+  // A SwiftError is passed in R12.
+  CCIfSwiftError<CCIfType<[i64], CCAssignToReg<[R12]>>>,
+
   // 128 bit vectors are passed by pointer
   CCIfType<[v16i8, v8i16, v4i32, v2i64, v4f32, v2f64], CCPassIndirect<i64>>,