Debug info: Factor out the creation of DWARF expressions from AsmPrinter

into a new class DwarfExpression that can be shared between AsmPrinter
and DwarfUnit.

This is the first step towards unifying the two entirely redundant
implementations of dwarf expression emission in DwarfUnit and AsmPrinter.

Almost no functional change — Testcases were updated because asm comments
that used to be on two lines now appear on the same line, which is
actually preferable.

llvm-svn: 225706

1 files changed, 143 insertions, 0 deletions

diff --git a/llvm/lib/CodeGen/AsmPrinter/DwarfExpression.cpp b/llvm/lib/CodeGen/AsmPrinter/DwarfExpression.cpp
new file mode 100644
index 00000000000..01c9e2497dd
--- /dev/null
+++ b/llvm/lib/CodeGen/AsmPrinter/DwarfExpression.cpp
@@ -0,0 +1,143 @@
+//===-- llvm/CodeGen/DwarfExpression.cpp - Dwarf Debug Framework ----------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This file contains support for writing dwarf debug info into asm files.
+//
+//===----------------------------------------------------------------------===//
+
+#include "DwarfExpression.h"
+#include "llvm/ADT/SmallBitVector.h"
+#include "llvm/Support/Dwarf.h"
+#include "llvm/Target/TargetMachine.h"
+#include "llvm/Target/TargetRegisterInfo.h"
+#include "llvm/Target/TargetSubtargetInfo.h"
+
+
+using namespace llvm;
+
+void DwarfExpression::AddReg(int DwarfReg, const char* Comment) {
+  assert(DwarfReg >= 0 && "invalid negative dwarf register number");
+  if (DwarfReg < 32) {
+    EmitOp(dwarf::DW_OP_reg0 + DwarfReg, Comment);
+  } else {
+    EmitOp(dwarf::DW_OP_regx, Comment);
+    EmitUnsigned(DwarfReg);
+  }
+}
+
+void DwarfExpression::AddRegIndirect(int DwarfReg, int Offset, bool Deref) {
+  assert(DwarfReg >= 0 && "invalid negative dwarf register number");
+  if (DwarfReg < 32) {
+    EmitOp(dwarf::DW_OP_breg0 + DwarfReg);
+  } else {
+    EmitOp(dwarf::DW_OP_bregx);
+    EmitUnsigned(DwarfReg);
+  }
+  EmitSigned(Offset);
+  if (Deref)
+    EmitOp(dwarf::DW_OP_deref);
+}
+
+void DwarfExpression::AddOpPiece(unsigned SizeInBits,
+                                 unsigned OffsetInBits) {
+  assert(SizeInBits > 0 && "piece has size zero");
+  const unsigned SizeOfByte = 8;
+  if (OffsetInBits > 0 || SizeInBits % SizeOfByte) {
+    EmitOp(dwarf::DW_OP_bit_piece);
+    EmitUnsigned(SizeInBits);
+    EmitUnsigned(OffsetInBits);
+  } else {
+    EmitOp(dwarf::DW_OP_piece);
+    unsigned ByteSize = SizeInBits / SizeOfByte;
+    EmitUnsigned(ByteSize);
+  }
+}
+
+void DwarfExpression::AddShr(unsigned ShiftBy) {
+  EmitOp(dwarf::DW_OP_constu);
+  EmitUnsigned(ShiftBy);
+  EmitOp(dwarf::DW_OP_shr);
+}
+
+void DwarfExpression::AddMachineRegPiece(unsigned MachineReg,
+                                         unsigned PieceSizeInBits,
+                                         unsigned PieceOffsetInBits) {
+  const TargetRegisterInfo *TRI = TM.getSubtargetImpl()->getRegisterInfo();
+  int Reg = TRI->getDwarfRegNum(MachineReg, false);
+
+  // If this is a valid register number, emit it.
+  if (Reg >= 0) {
+    AddReg(Reg);
+    AddOpPiece(PieceSizeInBits, PieceOffsetInBits);
+    return;
+  }
+
+  // Walk up the super-register chain until we find a valid number.
+  // For example, EAX on x86_64 is a 32-bit piece of RAX with offset 0.
+  for (MCSuperRegIterator SR(MachineReg, TRI); SR.isValid(); ++SR) {
+    Reg = TRI->getDwarfRegNum(*SR, false);
+    if (Reg >= 0) {
+      unsigned Idx = TRI->getSubRegIndex(*SR, MachineReg);
+      unsigned Size = TRI->getSubRegIdxSize(Idx);
+      unsigned RegOffset = TRI->getSubRegIdxOffset(Idx);
+      AddReg(Reg, "super-register");
+      if (PieceOffsetInBits == RegOffset) {
+        AddOpPiece(Size, RegOffset);
+      } else {
+        // If this is part of a variable in a sub-register at a
+        // non-zero offset, we need to manually shift the value into
+        // place, since the DW_OP_piece describes the part of the
+        // variable, not the position of the subregister.
+        if (RegOffset)
+          AddShr(RegOffset);
+        AddOpPiece(Size, PieceOffsetInBits);
+      }
+      return;
+    }
+  }
+
+  // Otherwise, attempt to find a covering set of sub-register numbers.
+  // For example, Q0 on ARM is a composition of D0+D1.
+  //
+  // Keep track of the current position so we can emit the more
+  // efficient DW_OP_piece.
+  unsigned CurPos = PieceOffsetInBits;
+  // The size of the register in bits, assuming 8 bits per byte.
+  unsigned RegSize = TRI->getMinimalPhysRegClass(MachineReg)->getSize() * 8;
+  // Keep track of the bits in the register we already emitted, so we
+  // can avoid emitting redundant aliasing subregs.
+  SmallBitVector Coverage(RegSize, false);
+  for (MCSubRegIterator SR(MachineReg, TRI); SR.isValid(); ++SR) {
+    unsigned Idx = TRI->getSubRegIndex(MachineReg, *SR);
+    unsigned Size = TRI->getSubRegIdxSize(Idx);
+    unsigned Offset = TRI->getSubRegIdxOffset(Idx);
+    Reg = TRI->getDwarfRegNum(*SR, false);
+
+    // Intersection between the bits we already emitted and the bits
+    // covered by this subregister.
+    SmallBitVector Intersection(RegSize, false);
+    Intersection.set(Offset, Offset + Size);
+    Intersection ^= Coverage;
+
+    // If this sub-register has a DWARF number and we haven't covered
+    // its range, emit a DWARF piece for it.
+    if (Reg >= 0 && Intersection.any()) {
+      AddReg(Reg, "sub-register");
+      AddOpPiece(Size, Offset == CurPos ? 0 : Offset);
+      CurPos = Offset + Size;
+
+      // Mark it as emitted.
+      Coverage.set(Offset, Offset + Size);
+    }
+  }
+
+  if (CurPos == PieceOffsetInBits)
+    // FIXME: We have no reasonable way of handling errors in here.
+    EmitOp(dwarf::DW_OP_nop, "nop (could not find a dwarf register number)");
+}