[AArch64] Implement support for windows style vararg functions

Pass parameters properly in calls to such functions (pass all
floats in integer registers), and handle va_start properly (allocate
stack immediately below the arguments on the stack, to save the
register arguments into a single continuous array).

Differential Revision: https://reviews.llvm.org/D35006

llvm-svn: 307928

1 files changed, 10 insertions, 1 deletions

diff --git a/llvm/lib/Target/AArch64/AArch64FrameLowering.cpp b/llvm/lib/Target/AArch64/AArch64FrameLowering.cpp
index e96ee7d29b3..2436c4eb76f 100644
--- a/llvm/lib/Target/AArch64/AArch64FrameLowering.cpp
+++ b/llvm/lib/Target/AArch64/AArch64FrameLowering.cpp
@@ -41,6 +41,10 @@
 // |                                   |
 // |-----------------------------------|
 // |                                   |
+// | (Win64 only) varargs from reg     |
+// |                                   |
+// |-----------------------------------|
+// |                                   |
 // | prev_fp, prev_lr                  |
 // | (a.k.a. "frame record")           |
 // |-----------------------------------| <- fp(=x29)
@@ -950,7 +954,12 @@ static void computeCalleeSaveRegisterPairs(
           CC == CallingConv::PreserveMost ||
           (Count & 1) == 0) &&
          "Odd number of callee-saved regs to spill!");
-  unsigned Offset = AFI->getCalleeSavedStackSize();
+  int Offset = AFI->getCalleeSavedStackSize();
+
+  unsigned GPRSaveSize = AFI->getVarArgsGPRSize();
+  const AArch64Subtarget &Subtarget = MF.getSubtarget<AArch64Subtarget>();
+  if (Subtarget.isTargetWindows())
+    Offset -= alignTo(GPRSaveSize, 16);
 
   for (unsigned i = 0; i < Count; ++i) {
     RegPairInfo RPI;