[PowerPC] Don't spill the frame pointer twice

When a function contains something, such as inline asm, which explicitly
clobbers the register used as the frame pointer, don't spill it twice. If we
need a frame pointer, it will be saved/restored in the prologue/epilogue code.
Explicitly spilling it again will reuse the same spill slot used by the
prologue/epilogue code, thus clobbering the saved value. The same applies
to the base-pointer or PIC-base register.

Partially fixes PR26856. Thanks to Ulrich for his analysis and the small
inline-asm reproducer.

llvm-svn: 280188

1 files changed, 11 insertions, 0 deletions

diff --git a/llvm/lib/Target/PowerPC/PPCFrameLowering.cpp b/llvm/lib/Target/PowerPC/PPCFrameLowering.cpp
index 1d8aaac46d3..c59c619e0bc 100644
--- a/llvm/lib/Target/PowerPC/PPCFrameLowering.cpp
+++ b/llvm/lib/Target/PowerPC/PPCFrameLowering.cpp
@@ -1419,6 +1419,17 @@ void PPCFrameLowering::determineCalleeSaves(MachineFunction &MF,
     FI->setPICBasePointerSaveIndex(PBPSI);
   }
 
+  // Make sure we don't explicitly spill r31, because, for example, we have
+  // some inline asm which explicity clobbers it, when we otherwise have a
+  // frame pointer and are using r31's spill slot for the prologue/epilogue
+  // code. Same goes for the base pointer and the PIC base register.
+  if (needsFP(MF))
+    SavedRegs.reset(isPPC64 ? PPC::X31 : PPC::R31);
+  if (RegInfo->hasBasePointer(MF))
+    SavedRegs.reset(RegInfo->getBaseRegister(MF));
+  if (FI->usesPICBase())
+    SavedRegs.reset(PPC::R30);
+
   // Reserve stack space to move the linkage area to in case of a tail call.
   int TCSPDelta = 0;
   if (MF.getTarget().Options.GuaranteedTailCallOpt &&