Factor the stack alignment calculations out into a target independent pass.

No functionality change.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@90336 91177308-0d34-0410-b5e6-96231b3b80d8

lib/CodeGen/MaxStackAlignment.cpp

@@ -0,0 +1,70 @@
+//===-- MaxStackAlignment.cpp - Compute the required stack alignment -- ---===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This pass looks for vector register usage and aligned local objects to
+// calculate the maximum required alignment for a function. This is used by
+// targets which support it to determine if dynamic stack realignment is
+// necessary.
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/CodeGen/MachineFunction.h"
+#include "llvm/CodeGen/MachineFrameInfo.h"
+#include "llvm/CodeGen/MachineRegisterInfo.h"
+#include "llvm/CodeGen/Passes.h"
+
+using namespace llvm;
+
+namespace {
+  struct MaximalStackAlignmentCalculator : public MachineFunctionPass {
+    static char ID;
+    MaximalStackAlignmentCalculator() : MachineFunctionPass(&ID) {}
+
+    virtual bool runOnMachineFunction(MachineFunction &MF) {
+      MachineFrameInfo *FFI = MF.getFrameInfo();
+      MachineRegisterInfo &RI = MF.getRegInfo();
+
+      // Calculate max stack alignment of all already allocated stack objects.
+      FFI->calculateMaxStackAlignment();
+      unsigned MaxAlign = FFI->getMaxAlignment();
+
+      // Be over-conservative: scan over all vreg defs and find whether vector
+      // registers are used. If yes, there is probability that vector registers
+      // will be spilled and thus the stack needs to be aligned properly.
+      // FIXME: It would be better to only do this if a spill actually
+      // happens rather than conseratively aligning the stack regardless.
+      for (unsigned RegNum = TargetRegisterInfo::FirstVirtualRegister;
+           RegNum < RI.getLastVirtReg(); ++RegNum)
+        MaxAlign = std::max(MaxAlign, RI.getRegClass(RegNum)->getAlignment());
+
+      if (FFI->getMaxAlignment() == MaxAlign)
+        return false;
+
+      FFI->setMaxAlignment(MaxAlign);
+      return true;
+    }
+
+    virtual const char *getPassName() const {
+      return "Stack Alignment Requirements Auto-Detector";
+    }
+
+    virtual void getAnalysisUsage(AnalysisUsage &AU) const {
+      AU.setPreservesCFG();
+      MachineFunctionPass::getAnalysisUsage(AU);
+    }
+  };
+
+  char MaximalStackAlignmentCalculator::ID = 0;
+}
+
+FunctionPass*
+llvm::createMaxStackAlignmentCalculatorPass() {
+  return new MaximalStackAlignmentCalculator();
+}
+