[SystemZ] Fix missing emergency spill slot corner case

We sometimes need emergency spill slots for the register scavenger.
This may be the case when code needs to access a stack slot that
has an offset of 4096 or more relative to the stack pointer.

To make that determination, processFunctionBeforeFrameFinalized
currently simply checks the total stack frame size of the current
function.  But this is not enough, since code may need to access
stack slots in the caller's stack frame as well, in particular
incoming arguments stored on the stack.

This commit fixes the problem by taking argument slots into account.

llvm-svn: 306305

1 files changed, 15 insertions, 2 deletions

diff --git a/llvm/lib/Target/SystemZ/SystemZFrameLowering.cpp b/llvm/lib/Target/SystemZ/SystemZFrameLowering.cpp
index a28a91e834f..0cb2b5a14ce 100644
--- a/llvm/lib/Target/SystemZ/SystemZFrameLowering.cpp
+++ b/llvm/lib/Target/SystemZ/SystemZFrameLowering.cpp
@@ -277,8 +277,21 @@ void SystemZFrameLowering::
 processFunctionBeforeFrameFinalized(MachineFunction &MF,
                                     RegScavenger *RS) const {
   MachineFrameInfo &MFFrame = MF.getFrameInfo();
-  uint64_t MaxReach = (MFFrame.estimateStackSize(MF) +
-                       SystemZMC::CallFrameSize * 2);
+  // Get the size of our stack frame to be allocated ...
+  uint64_t StackSize = (MFFrame.estimateStackSize(MF) +
+                        SystemZMC::CallFrameSize);
+  // ... and the maximum offset we may need to reach into the
+  // caller's frame to access the save area or stack arguments.
+  int64_t MaxArgOffset = SystemZMC::CallFrameSize;
+  for (int I = MFFrame.getObjectIndexBegin(); I != 0; ++I)
+    if (MFFrame.getObjectOffset(I) >= 0) {
+      int64_t ArgOffset = SystemZMC::CallFrameSize +
+                          MFFrame.getObjectOffset(I) +
+                          MFFrame.getObjectSize(I);
+      MaxArgOffset = std::max(MaxArgOffset, ArgOffset);
+    }
+
+  uint64_t MaxReach = StackSize + MaxArgOffset;
   if (!isUInt<12>(MaxReach)) {
     // We may need register scavenging slots if some parts of the frame
     // are outside the reach of an unsigned 12-bit displacement.