Teach MachineFrameInfo to track maximum alignment while stack objects are being

created. This ensures it's updated at all time. It means targets which perform
dynamic stack alignment would know whether it is required and whether frame
pointer register cannot be made available register allocation.
This is a fix for rdar://7625239. Sorry, I can't create a reasonably sized test
case.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@96069 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/CodeGen/MachineFrameInfo.h

@@ -276,6 +276,7 @@ public:
     assert(unsigned(ObjectIdx+NumFixedObjects) < Objects.size() &&
            "Invalid Object Idx!");
     Objects[ObjectIdx+NumFixedObjects].Alignment = Align;
+    MaxAlignment = std::max(MaxAlignment, Align);
   }
 
   /// getObjectOffset - Return the assigned stack offset of the specified object
@@ -328,19 +329,6 @@ public:
   ///
   void setMaxAlignment(unsigned Align) { MaxAlignment = Align; }
 
-  /// calculateMaxStackAlignment() - If there is a local object which requires
-  /// greater alignment than the current max alignment, adjust accordingly.
-  void calculateMaxStackAlignment() {
-    for (int i = getObjectIndexBegin(),
-         e = getObjectIndexEnd(); i != e; ++i) {
-      if (isDeadObjectIndex(i))
-        continue;
-
-      unsigned Align = getObjectAlignment(i);
-      MaxAlignment = std::max(MaxAlignment, Align);
-    }
-  }
-
   /// hasCalls - Return true if the current function has no function calls.
   /// This is only valid during or after prolog/epilog code emission.
   ///
@@ -402,6 +390,7 @@ public:
     Objects.push_back(StackObject(Size, Alignment, 0, false, isSS));
     int Index = (int)Objects.size()-NumFixedObjects-1;
     assert(Index >= 0 && "Bad frame index!");
+    MaxAlignment = std::max(MaxAlignment, Alignment);
     return Index;
   }
 
@@ -412,6 +401,7 @@ public:
   int CreateSpillStackObject(uint64_t Size, unsigned Alignment) {
     CreateStackObject(Size, Alignment, true);
     int Index = (int)Objects.size()-NumFixedObjects-1;
+    MaxAlignment = std::max(MaxAlignment, Alignment);
     return Index;
   }
 

lib/CodeGen/PrologEpilogInserter.cpp

@@ -476,8 +476,6 @@ void PEI::calculateFrameObjectOffsets(MachineFunction &Fn) {
   // Loop over all of the stack objects, assigning sequential addresses...
   MachineFrameInfo *FFI = Fn.getFrameInfo();
 
-  unsigned MaxAlign = 1;
-
   // Start at the beginning of the local area.
   // The Offset is the distance from the stack top in the direction
   // of stack growth -- so it's always nonnegative.
@@ -517,9 +515,6 @@ void PEI::calculateFrameObjectOffsets(MachineFunction &Fn) {
       Offset += FFI->getObjectSize(i);
 
       unsigned Align = FFI->getObjectAlignment(i);
-      // If the alignment of this object is greater than that of the stack,
-      // then increase the stack alignment to match.
-      MaxAlign = std::max(MaxAlign, Align);
       // Adjust to alignment boundary
       Offset = (Offset+Align-1)/Align*Align;
 
@@ -529,9 +524,6 @@ void PEI::calculateFrameObjectOffsets(MachineFunction &Fn) {
     int MaxCSFI = MaxCSFrameIndex, MinCSFI = MinCSFrameIndex;
     for (int i = MaxCSFI; i >= MinCSFI ; --i) {
       unsigned Align = FFI->getObjectAlignment(i);
-      // If the alignment of this object is greater than that of the stack,
-      // then increase the stack alignment to match.
-      MaxAlign = std::max(MaxAlign, Align);
       // Adjust to alignment boundary
       Offset = (Offset+Align-1)/Align*Align;
 
@@ -540,6 +532,8 @@ void PEI::calculateFrameObjectOffsets(MachineFunction &Fn) {
     }
   }
 
+  unsigned MaxAlign = FFI->getMaxAlignment();
+
   // Make sure the special register scavenging spill slot is closest to the
   // frame pointer if a frame pointer is required.
   const TargetRegisterInfo *RegInfo = Fn.getTarget().getRegisterInfo();
@@ -605,11 +599,6 @@ void PEI::calculateFrameObjectOffsets(MachineFunction &Fn) {
 
   // Update frame info to pretend that this is part of the stack...
   FFI->setStackSize(Offset - LocalAreaOffset);
-
-  // Remember the required stack alignment in case targets need it to perform
-  // dynamic stack alignment.
-  if (MaxAlign > FFI->getMaxAlignment())
-    FFI->setMaxAlignment(MaxAlign);
 }
 
 

lib/Target/ARM/ARMBaseRegisterInfo.cpp

@@ -583,14 +583,6 @@ ARMBaseRegisterInfo::processFunctionBeforeCalleeSavedScan(MachineFunction &MF,
   SmallVector<unsigned, 4> UnspilledCS2GPRs;
   ARMFunctionInfo *AFI = MF.getInfo<ARMFunctionInfo>();
 
-
-  // Calculate and set max stack object alignment early, so we can decide
-  // whether we will need stack realignment (and thus FP).
-  if (RealignStack) {
-    MachineFrameInfo *MFI = MF.getFrameInfo();
-    MFI->calculateMaxStackAlignment();
-  }
-
   // Spill R4 if Thumb2 function requires stack realignment - it will be used as
   // scratch register.
   // FIXME: It will be better just to find spare register here.

lib/Target/X86/X86RegisterInfo.cpp

@@ -485,7 +485,7 @@ X86RegisterInfo::getFrameIndexOffset(const MachineFunction &MF, int FI) const {
       Offset += SlotSize;
     } else {
       unsigned Align = MFI->getObjectAlignment(FI);
-      assert( (-(Offset + StackSize)) % Align == 0);
+      assert((-(Offset + StackSize)) % Align == 0);
       Align = 0;
       return Offset + StackSize;
     }
@@ -627,10 +627,6 @@ X86RegisterInfo::processFunctionBeforeCalleeSavedScan(MachineFunction &MF,
                                                       RegScavenger *RS) const {
   MachineFrameInfo *MFI = MF.getFrameInfo();
 
-  // Calculate and set max stack object alignment early, so we can decide
-  // whether we will need stack realignment (and thus FP).
-  MFI->calculateMaxStackAlignment();
-
   X86MachineFunctionInfo *X86FI = MF.getInfo<X86MachineFunctionInfo>();
   int32_t TailCallReturnAddrDelta = X86FI->getTCReturnAddrDelta();