Update local stack block allocation to let PEI do the allocs if no additional

base registers were required. This will allow for slightly better packing
of the locals when alignment padding is necessary after callee saved registers.

llvm-svn: 111508

Author: Jim Grosbach

llvm/include/llvm/CodeGen/MachineFrameInfo.h

@@ -216,6 +216,11 @@ class MachineFrameInfo {
   /// alignment of any object in it.
   unsigned LocalFrameMaxAlign;
 
+  /// Whether the local object blob needs to be allocated together. If not,
+  /// PEI should ignore the isPreAllocated flags on the stack objects and
+  /// just allocate them normally.
+  bool UseLocalStackAllocationBlock;
+
 public:
     explicit MachineFrameInfo(const TargetFrameInfo &tfi) : TFI(tfi) {
     StackSize = NumFixedObjects = OffsetAdjustment = MaxAlignment = 0;
@@ -315,6 +320,17 @@ class MachineFrameInfo {
   /// object blob.
   unsigned getLocalFrameMaxAlign() { return LocalFrameMaxAlign; }
 
+  /// getUseLocalStackAllocationBlock - Get whether the local allocation blob
+  /// should be allocated together or let PEI allocate the locals in it
+  /// directly.
+  bool getUseLocalStackAllocationBlock() {return UseLocalStackAllocationBlock;}
+
+  /// setUseLocalStackAllocationBlock - Set whether the local allocation blob
+  /// should be allocated together or let PEI allocate the locals in it
+  /// directly.
+  void setUseLocalStackAllocationBlock(bool v) {
+    UseLocalStackAllocationBlock = v;
+  }
 
   /// isObjectPreAllocated - Return true if the object was pre-allocated into
   /// the local block.

llvm/lib/CodeGen/LocalStackSlotAllocation.cpp

@@ -89,6 +89,13 @@ bool LocalStackSlotPass::runOnMachineFunction(MachineFunction &MF) {
   // Insert virtual base registers to resolve frame index references.
   insertFrameReferenceRegisters(MF);
 
+  // Tell MFI whether any base registers were allocated. PEI will only
+  // want to use the local block allocations from this pass if there were any.
+  // Otherwise, PEI can do a bit better job of getting the alignment right
+  // without a hole at the start since it knows the alignment of the stack
+  // at the start of local allocation, and this pass doesn't.
+  MFI->setUseLocalStackAllocationBlock(NumBaseRegisters > 0);
+
   return true;
 }
 

llvm/lib/CodeGen/PrologEpilogInserter.cpp

@@ -560,7 +560,7 @@ void PEI::calculateFrameObjectOffsets(MachineFunction &Fn) {
   // check for whether the frame is large enough to want to use virtual
   // frame index registers. Functions which don't want/need this optimization
   // will continue to use the existing code path.
-  if (EnableLocalStackAlloc && MFI->getLocalFrameSize()) {
+  if (EnableLocalStackAlloc && MFI->getUseLocalStackAllocationBlock()) {
     unsigned Align = MFI->getLocalFrameMaxAlign();
 
     // Adjust to alignment boundary.
@@ -593,7 +593,8 @@ void PEI::calculateFrameObjectOffsets(MachineFunction &Fn) {
 
     // Assign large stack objects first.
     for (unsigned i = 0, e = MFI->getObjectIndexEnd(); i != e; ++i) {
-      if (MFI->isObjectPreAllocated(i))
+      if (MFI->isObjectPreAllocated(i) &&
+          MFI->getUseLocalStackAllocationBlock())
         continue;
       if (i >= MinCSFrameIndex && i <= MaxCSFrameIndex)
         continue;
@@ -614,7 +615,8 @@ void PEI::calculateFrameObjectOffsets(MachineFunction &Fn) {
   // Then assign frame offsets to stack objects that are not used to spill
   // callee saved registers.
   for (unsigned i = 0, e = MFI->getObjectIndexEnd(); i != e; ++i) {
-    if (MFI->isObjectPreAllocated(i))
+    if (MFI->isObjectPreAllocated(i) &&
+        MFI->getUseLocalStackAllocationBlock())
       continue;
     if (i >= MinCSFrameIndex && i <= MaxCSFrameIndex)
       continue;