PPC: Support dynamic allocas with large alignment

Support for dynamic stack alignments in the PPC backend has been unfinished, in
part because it depends on dynamic stack realignment (which I only just
recently implemented fully). Now we can also support dynamic allocas with
higher than the default target stack alignment (16 bytes).

In order to round-up the requested size to the maximum requested alignment, we
need an additional register to hold the rounded-up size. We're already using one
scavenged register to hold the previous stack-pointer value (which needs to be
stored with the signal-safe stdux update), and so when we have dynamic allocas
and a large alignment, we allocate two emergency spill slots for the scavenger.

llvm-svn: 186562

1 files changed, 5 insertions, 1 deletions

diff --git a/llvm/lib/Target/PowerPC/PPCFrameLowering.cpp b/llvm/lib/Target/PowerPC/PPCFrameLowering.cpp
index d846365..24d3a0b 100644
--- a/llvm/lib/Target/PowerPC/PPCFrameLowering.cpp
+++ b/llvm/lib/Target/PowerPC/PPCFrameLowering.cpp
@@ -1237,8 +1237,12 @@ PPCFrameLowering::addScavengingSpillSlot(MachineFunction &MF,
                                                        RC->getAlignment(),
                                                        false));
 
+    // Might we have over-aligned allocas?
+    bool HasAlVars = MFI->hasVarSizedObjects() &&
+                     MFI->getMaxAlignment() > getStackAlignment();
+
     // These kinds of spills might need two registers.
-    if (spillsCR(MF) || spillsVRSAVE(MF))
+    if (spillsCR(MF) || spillsVRSAVE(MF) || HasAlVars)
       RS->addScavengingFrameIndex(MFI->CreateStackObject(RC->getSize(),
                                                          RC->getAlignment(),
                                                          false));