Merging r196046:

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r196046 | tnorthover | 2013-12-01 06:16:24 -0800 (Sun, 01 Dec 2013) | 8 lines

ARM: fix bug in -Oz stack adjustment folding

Previously, we clobbered callee-saved registers when folding an "add
sp, #N" into a "pop {rD, ...}" instruction. This change checks whether
a register we're going to add to the "pop" could actually be live
outside the function before doing so and should fix the issue.

This should fix PR18081.
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git-svn-id: https://llvm.org/svn/llvm-project/llvm/branches/release_34@196074 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 18 insertions, 7 deletions

diff --git a/lib/Target/ARM/ARMBaseInstrInfo.cpp b/lib/Target/ARM/ARMBaseInstrInfo.cpp
index 67534c4a44..df8c017515 100644
--- a/lib/Target/ARM/ARMBaseInstrInfo.cpp
+++ b/lib/Target/ARM/ARMBaseInstrInfo.cpp
@@ -1913,29 +1913,40 @@ bool llvm::tryFoldSPUpdateIntoPushPop(MachineFunction &MF,
 
   MachineBasicBlock *MBB = MI->getParent();
   const TargetRegisterInfo *TRI = MF.getRegInfo().getTargetRegisterInfo();
+  const MCPhysReg *CSRegs = TRI->getCalleeSavedRegs(&MF);
 
   // Now try to find enough space in the reglist to allocate NumBytes.
   for (unsigned CurReg = FirstReg - 1; CurReg >= RD0Reg && RegsNeeded;
-       --CurReg, --RegsNeeded) {
+       --CurReg) {
     if (!IsPop) {
       // Pushing any register is completely harmless, mark the
       // register involved as undef since we don't care about it in
       // the slightest.
       RegList.push_back(MachineOperand::CreateReg(CurReg, false, false,
                                                   false, false, true));
+      --RegsNeeded;
       continue;
     }
 
-    // However, we can only pop an extra register if it's not live. Otherwise we
-    // might clobber a return value register. We assume that once we find a live
-    // return register all lower ones will be too so there's no use proceeding.
-    if (MBB->computeRegisterLiveness(TRI, CurReg, MI) !=
-        MachineBasicBlock::LQR_Dead)
-      return false;
+    // However, we can only pop an extra register if it's not live. For
+    // registers live within the function we might clobber a return value
+    // register; the other way a register can be live here is if it's
+    // callee-saved.
+    if (isCalleeSavedRegister(CurReg, CSRegs) ||
+        MBB->computeRegisterLiveness(TRI, CurReg, MI) !=
+            MachineBasicBlock::LQR_Dead) {
+      // VFP pops don't allow holes in the register list, so any skip is fatal
+      // for our transformation. GPR pops do, so we should just keep looking.
+      if (IsVFPPushPop)
+        return false;
+      else
+        continue;
+    }
 
     // Mark the unimportant registers as <def,dead> in the POP.
     RegList.push_back(MachineOperand::CreateReg(CurReg, true, false, false,
                                                 true));
+    --RegsNeeded;
   }
 
   if (RegsNeeded > 0)