Fix coordination for using R4 in Thumb1 as a scratch for SP restore.

The logic for reserving R4 for use as a scratch needs to match that for
actually using it. Also, it's not necessary for immediate <=508, so adjust
the value checked.



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@132934 91177308-0d34-0410-b5e6-96231b3b80d8

2 files changed, 9 insertions, 4 deletions

diff --git a/lib/Target/ARM/ARMFrameLowering.cpp b/lib/Target/ARM/ARMFrameLowering.cpp
index e2e95d47b3..516e34ae04 100644
--- a/lib/Target/ARM/ARMFrameLowering.cpp
+++ b/lib/Target/ARM/ARMFrameLowering.cpp
@@ -841,9 +841,14 @@ ARMFrameLowering::processFunctionBeforeCalleeSavedScan(MachineFunction &MF,
     if (AFI->getVarArgsRegSaveSize() > 0)
       MF.getRegInfo().setPhysRegUsed(ARM::LR);
 
-    // Spill R4 if Thumb1 epilogue has to restore SP from FP since 
+    // Spill R4 if Thumb1 epilogue has to restore SP from FP. We don't know
+    // for sure what the stack size will be, but for this, an estimate is good
+    // enough. If there anything changes it, it'll be a spill, which implies
+    // we've used all the registers and so R4 is already used, so not marking
+    // it here will be OK.
     // FIXME: It will be better just to find spare register here.
-    if (MFI->hasVarSizedObjects())
+    unsigned StackSize = estimateStackSize(MF);
+    if (MFI->hasVarSizedObjects() || StackSize > 508)
       MF.getRegInfo().setPhysRegUsed(ARM::R4);
   }
 
diff --git a/lib/Target/ARM/Thumb1FrameLowering.cpp b/lib/Target/ARM/Thumb1FrameLowering.cpp
index dee3d27820..e56d48168c 100644
--- a/lib/Target/ARM/Thumb1FrameLowering.cpp
+++ b/lib/Target/ARM/Thumb1FrameLowering.cpp
@@ -136,8 +136,8 @@ void Thumb1FrameLowering::emitPrologue(MachineFunction &MF) const {
     BuildMI(MBB, MBBI, dl, TII.get(ARM::tADDrSPi), FramePtr)
       .addFrameIndex(FramePtrSpillFI).addImm(0)
       .setMIFlags(MachineInstr::FrameSetup);
-    if (NumBytes > 7)
-      // If offset is > 7 then sp cannot be adjusted in a single instruction,
+    if (NumBytes > 508)
+      // If offset is > 508 then sp cannot be adjusted in a single instruction,
       // try restoring from fp instead.
       AFI->setShouldRestoreSPFromFP(true);
   }