Revert "Reapply D70800: Fix AArch64 AAPCS frame record chain"

This reverts commit 9936455.

That commit caused failed assertions e.g. like this:

$ cat alloca.c
a;
b() {
  float c;
  d();
  a = __builtin_alloca(d);
  c = e();
  f(a);
  return c;
}
$ clang -target aarch64-linux-gnu -c alloca.c -O2
clang: ../lib/Target/AArch64/AArch64InstrInfo.cpp:3446: void
llvm::emitFrameOffset(llvm::MachineBasicBlock&,
llvm::MachineBasicBlock::iterator, const llvm::DebugLoc&, unsigned int,
unsigned int, llvm::StackOffset, const llvm::TargetInstrInfo*,
llvm::MachineInstr::MIFlag, bool, bool, bool*):
Assertion `(DestReg != AArch64::SP || Bytes % 16 == 0) &&
"SP increment/decrement not 16-byte aligned"' failed.

llvm/lib/Target/AArch64/AArch64FrameLowering.cpp

@@ -1024,6 +1024,10 @@ static bool needsWinCFI(const MachineFunction &MF) {
          F.needsUnwindTableEntry();
 }
 
+static bool isTargetDarwin(const MachineFunction &MF) {
+  return MF.getSubtarget<AArch64Subtarget>().isTargetDarwin();
+}
+
 static bool isTargetWindows(const MachineFunction &MF) {
   return MF.getSubtarget<AArch64Subtarget>().isTargetWindows();
 }
@@ -1181,7 +1185,7 @@ void AArch64FrameLowering::emitPrologue(MachineFunction &MF,
   // For funclets the FP belongs to the containing function.
   if (!IsFunclet && HasFP) {
     // Only set up FP if we actually need to.
-    int64_t FPOffset = AFI->getCalleeSaveBaseToFrameRecordOffset();
+    int64_t FPOffset = isTargetDarwin(MF) ? (AFI->getCalleeSavedStackSize() - 16) : 0;
 
     if (CombineSPBump)
       FPOffset += AFI->getLocalStackSize();
@@ -1405,6 +1409,11 @@ void AArch64FrameLowering::emitPrologue(MachineFunction &MF,
   }
 
   if (needsFrameMoves) {
+    const DataLayout &TD = MF.getDataLayout();
+    const int StackGrowth = isTargetDarwin(MF)
+                                ? (2 * -TD.getPointerSize(0))
+                                : -AFI->getCalleeSavedStackSize();
+    Register FramePtr = RegInfo->getFrameRegister(MF);
     // An example of the prologue:
     //
     //     .globl __foo
@@ -1472,15 +1481,10 @@ void AArch64FrameLowering::emitPrologue(MachineFunction &MF,
     //     .cfi_offset w28, -32
 
     if (HasFP) {
-      const int OffsetToFirstCalleeSaveFromFP =
-          AFI->getCalleeSaveBaseToFrameRecordOffset() -
-          AFI->getCalleeSavedStackSize();
-      Register FramePtr = RegInfo->getFrameRegister(MF);
-
       // Define the current CFA rule to use the provided FP.
       unsigned Reg = RegInfo->getDwarfRegNum(FramePtr, true);
       unsigned CFIIndex = MF.addFrameInst(
-          MCCFIInstruction::cfiDefCfa(nullptr, Reg, FixedObject - OffsetToFirstCalleeSaveFromFP));
+          MCCFIInstruction::cfiDefCfa(nullptr, Reg, FixedObject - StackGrowth));
       BuildMI(MBB, MBBI, DL, TII->get(TargetOpcode::CFI_INSTRUCTION))
           .addCFIIndex(CFIIndex)
           .setMIFlags(MachineInstr::FrameSetup);
@@ -1771,8 +1775,10 @@ void AArch64FrameLowering::emitEpilogue(MachineFunction &MF,
   // non-post-indexed loads for the restores if we aren't actually going to
   // be able to save any instructions.
   if (!IsFunclet && (MFI.hasVarSizedObjects() || AFI->isStackRealigned())) {
+    int64_t OffsetToFrameRecord =
+        isTargetDarwin(MF) ? (-(int64_t)AFI->getCalleeSavedStackSize() + 16) : 0;
     emitFrameOffset(MBB, LastPopI, DL, AArch64::SP, AArch64::FP,
-                    {-AFI->getCalleeSaveBaseToFrameRecordOffset(), MVT::i8},
+                    {OffsetToFrameRecord, MVT::i8},
                     TII, MachineInstr::FrameDestroy, false, NeedsWinCFI);
   } else if (NumBytes)
     emitFrameOffset(MBB, LastPopI, DL, AArch64::SP, AArch64::SP,
@@ -1833,11 +1839,11 @@ static StackOffset getFPOffset(const MachineFunction &MF, int64_t ObjectOffset)
   const auto &Subtarget = MF.getSubtarget<AArch64Subtarget>();
   bool IsWin64 =
       Subtarget.isCallingConvWin64(MF.getFunction().getCallingConv());
+
   unsigned FixedObject =
       getFixedObjectSize(MF, AFI, IsWin64, /*IsFunclet=*/false);
-  int64_t CalleeSaveSize = AFI->getCalleeSavedStackSize(MF.getFrameInfo());
-  int64_t FPAdjust =
-      CalleeSaveSize - AFI->getCalleeSaveBaseToFrameRecordOffset();
+  unsigned FPAdjust = isTargetDarwin(MF)
+                        ? 16 : AFI->getCalleeSavedStackSize(MF.getFrameInfo());
   return {ObjectOffset + FixedObject + FPAdjust, MVT::i8};
 }
 
@@ -2225,14 +2231,6 @@ static void computeCalleeSaveRegisterPairs(
             (RPI.isScalable() && RPI.Offset >= -256 && RPI.Offset <= 255)) &&
            "Offset out of bounds for LDP/STP immediate");
 
-    // Save the offset to frame record so that the FP register can point to the
-    // innermost frame record (spilled FP and LR registers).
-    if (NeedsFrameRecord && ((!IsWindows && RPI.Reg1 == AArch64::LR &&
-                              RPI.Reg2 == AArch64::FP) ||
-                             (IsWindows && RPI.Reg1 == AArch64::FP &&
-                              RPI.Reg2 == AArch64::LR)))
-      AFI->setCalleeSaveBaseToFrameRecordOffset(Offset);
-
     RegPairs.push_back(RPI);
     if (RPI.isPaired())
       ++i;

llvm/lib/Target/AArch64/AArch64MachineFunctionInfo.h

@@ -135,10 +135,6 @@ class AArch64FunctionInfo final : public MachineFunctionInfo {
   /// e.g. Tail Call, Thunk, or Function if none apply.
   Optional<std::string> OutliningStyle;
 
-  // Offset from SP-after-callee-saved-spills (i.e. SP-at-entry minus
-  // CalleeSavedStackSize) to the address of the frame record.
-  int CalleeSaveBaseToFrameRecordOffset = 0;
-
 public:
   AArch64FunctionInfo() = default;
 
@@ -342,13 +338,6 @@ class AArch64FunctionInfo final : public MachineFunctionInfo {
     TaggedBasePointerOffset = Offset;
   }
 
-  int getCalleeSaveBaseToFrameRecordOffset() const {
-    return CalleeSaveBaseToFrameRecordOffset;
-  }
-  void setCalleeSaveBaseToFrameRecordOffset(int Offset) {
-    CalleeSaveBaseToFrameRecordOffset = Offset;
-  }
-
 private:
   // Hold the lists of LOHs.
   MILOHContainer LOHContainerSet;