Add a local stack object block allocation pass. This is still an

experimental pass that allocates locals relative to one another before
register allocation and then assigns them to actual stack slots as a block
later in PEI. This will eventually allow targets with limited index offset
range to allocate additional base registers (not just FP and SP) to
more efficiently reference locals, as well as handle situations where
locals cannot be referenced via SP or FP at all (dynamic stack realignment
together with variable sized objects, for example). It's currently
incomplete and almost certainly buggy. Work in progress.

Disabled by default and gated via the -enable-local-stack-alloc command
line option.

rdar://8277890



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@111059 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 169 insertions, 0 deletions

diff --git a/lib/CodeGen/LocalStackSlotAllocation.cpp b/lib/CodeGen/LocalStackSlotAllocation.cpp
new file mode 100644
index 0000000000..dabfb469c3
--- /dev/null
+++ b/lib/CodeGen/LocalStackSlotAllocation.cpp
@@ -0,0 +1,169 @@
+//===- LocalStackSlotAllocation.cpp - Pre-allocate locals to stack slots --===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This pass assigns local frame indices to stack slots relative to one another
+// and allocates additional base registers to access them when the target
+// estimates the are likely to be out of range of stack pointer and frame
+// pointer relative addressing.
+//
+//===----------------------------------------------------------------------===//
+
+#define DEBUG_TYPE "localstackalloc"
+#include "llvm/Constants.h"
+#include "llvm/DerivedTypes.h"
+#include "llvm/Instructions.h"
+#include "llvm/Intrinsics.h"
+#include "llvm/ADT/Statistic.h"
+#include "llvm/LLVMContext.h"
+#include "llvm/Module.h"
+#include "llvm/Pass.h"
+#include "llvm/ADT/SmallSet.h"
+#include "llvm/CodeGen/MachineFrameInfo.h"
+#include "llvm/CodeGen/MachineFunction.h"
+#include "llvm/CodeGen/MachineFunctionPass.h"
+#include "llvm/CodeGen/Passes.h"
+#include "llvm/Support/Debug.h"
+#include "llvm/Support/ErrorHandling.h"
+#include "llvm/Support/raw_ostream.h"
+#include "llvm/Target/TargetRegisterInfo.h"
+#include "llvm/Target/TargetFrameInfo.h"
+
+using namespace llvm;
+
+STATISTIC(NumAllocations, "Number of frame indices processed");
+
+namespace {
+  class LocalStackSlotPass: public MachineFunctionPass {
+    int64_t LocalStackSize;
+
+    void calculateFrameObjectOffsets(MachineFunction &Fn);
+  public:
+    static char ID; // Pass identification, replacement for typeid
+    explicit LocalStackSlotPass() : MachineFunctionPass(ID) { }
+    bool runOnMachineFunction(MachineFunction &MF);
+
+    virtual void getAnalysisUsage(AnalysisUsage &AU) const {
+      AU.setPreservesCFG();
+      MachineFunctionPass::getAnalysisUsage(AU);
+    }
+    const char *getPassName() const {
+      return "Local Stack Slot Allocation";
+    }
+
+  private:
+  };
+} // end anonymous namespace
+
+char LocalStackSlotPass::ID = 0;
+
+FunctionPass *llvm::createLocalStackSlotAllocationPass() {
+  return new LocalStackSlotPass();
+}
+
+bool LocalStackSlotPass::runOnMachineFunction(MachineFunction &MF) {
+  calculateFrameObjectOffsets(MF);
+  DEBUG(dbgs() << LocalStackSize << " bytes of local storage pre-allocated\n");
+  return true;
+}
+
+/// AdjustStackOffset - Helper function used to adjust the stack frame offset.
+static inline void
+AdjustStackOffset(MachineFrameInfo *MFI, int FrameIdx, int64_t &Offset,
+                  unsigned &MaxAlign) {
+  unsigned Align = MFI->getObjectAlignment(FrameIdx);
+
+  // 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;
+
+  DEBUG(dbgs() << "Allocate FI(" << FrameIdx << ") to local offset "
+        << Offset << "\n");
+  MFI->mapLocalFrameObject(FrameIdx, Offset);
+  Offset += MFI->getObjectSize(FrameIdx);
+
+  ++NumAllocations;
+}
+
+/// calculateFrameObjectOffsets - Calculate actual frame offsets for all of the
+/// abstract stack objects.
+///
+void LocalStackSlotPass::calculateFrameObjectOffsets(MachineFunction &Fn) {
+  const TargetFrameInfo &TFI = *Fn.getTarget().getFrameInfo();
+
+  // Loop over all of the stack objects, assigning sequential addresses...
+  MachineFrameInfo *MFI = Fn.getFrameInfo();
+  int64_t Offset = 0;
+  unsigned MaxAlign = MFI->getMaxAlignment();
+
+  // Make sure that the stack protector comes before the local variables on the
+  // stack.
+  SmallSet<int, 16> LargeStackObjs;
+  if (MFI->getStackProtectorIndex() >= 0) {
+    AdjustStackOffset(MFI, MFI->getStackProtectorIndex(), Offset, MaxAlign);
+
+    // Assign large stack objects first.
+    for (unsigned i = 0, e = MFI->getObjectIndexEnd(); i != e; ++i) {
+      if (MFI->isDeadObjectIndex(i))
+        continue;
+      if (MFI->getStackProtectorIndex() == (int)i)
+        continue;
+      if (!MFI->MayNeedStackProtector(i))
+        continue;
+
+      AdjustStackOffset(MFI, i, Offset, MaxAlign);
+      LargeStackObjs.insert(i);
+    }
+  }
+
+  // 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->isDeadObjectIndex(i))
+      continue;
+    if (MFI->getStackProtectorIndex() == (int)i)
+      continue;
+    if (LargeStackObjs.count(i))
+      continue;
+
+    AdjustStackOffset(MFI, i, Offset, MaxAlign);
+  }
+
+  const TargetRegisterInfo *RegInfo = Fn.getTarget().getRegisterInfo();
+  if (!RegInfo->targetHandlesStackFrameRounding()) {
+    // If we have reserved argument space for call sites in the function
+    // immediately on entry to the current function, count it as part of the
+    // overall stack size.
+    if (MFI->adjustsStack() && RegInfo->hasReservedCallFrame(Fn))
+      Offset += MFI->getMaxCallFrameSize();
+
+    // Round up the size to a multiple of the alignment.  If the function has
+    // any calls or alloca's, align to the target's StackAlignment value to
+    // ensure that the callee's frame or the alloca data is suitably aligned;
+    // otherwise, for leaf functions, align to the TransientStackAlignment
+    // value.
+    unsigned StackAlign;
+    if (MFI->adjustsStack() || MFI->hasVarSizedObjects() ||
+        (RegInfo->needsStackRealignment(Fn) && MFI->getObjectIndexEnd() != 0))
+      StackAlign = TFI.getStackAlignment();
+    else
+      StackAlign = TFI.getTransientStackAlignment();
+
+    // If the frame pointer is eliminated, all frame offsets will be relative to
+    // SP not FP. Align to MaxAlign so this works.
+    StackAlign = std::max(StackAlign, MaxAlign);
+    unsigned AlignMask = StackAlign - 1;
+    Offset = (Offset + AlignMask) & ~uint64_t(AlignMask);
+  }
+
+  // Remember how big this blob of stack space is
+  LocalStackSize = Offset;
+}