DwarfDebug: Support floating point constants in location lists.

This patch closes a gap in the DWARF backend that caused LLVM to drop
debug info for floating point variables that were constant for part of
their scope. Floating point constants are emitted as one or more
DW_OP_constu joined via DW_OP_piece.

This fixes a regression caught by the LLDB testsuite that I introduced
in r262247 when we stopped blindly expanding the range of singular
DBG_VALUEs to span the entire scope and started to emit location lists
with accurate ranges instead.

Also deletes a now-impossible testcase (debug-loc-empty-entries).

<rdar://problem/25448338>

llvm-svn: 265760

1 files changed, 23 insertions, 15 deletions

diff --git a/llvm/lib/CodeGen/AsmPrinter/DwarfExpression.cpp b/llvm/lib/CodeGen/AsmPrinter/DwarfExpression.cpp
index 7b5b831da16..0608e05edd5 100644
--- a/llvm/lib/CodeGen/AsmPrinter/DwarfExpression.cpp
+++ b/llvm/lib/CodeGen/AsmPrinter/DwarfExpression.cpp
@@ -159,29 +159,37 @@ bool DwarfExpression::AddMachineRegPiece(unsigned MachineReg,
   return CurPos > PieceOffsetInBits;
 }
 
+void DwarfExpression::AddStackValue() {
+  if (DwarfVersion >= 4)
+    EmitOp(dwarf::DW_OP_stack_value);
+}
+
 void DwarfExpression::AddSignedConstant(int Value) {
   EmitOp(dwarf::DW_OP_consts);
   EmitSigned(Value);
-  // The proper way to describe a constant value is
-  // DW_OP_constu <const>, DW_OP_stack_value.
-  // Unfortunately, DW_OP_stack_value was not available until DWARF-4,
-  // so we will continue to generate DW_OP_constu <const> for DWARF-2
-  // and DWARF-3. Technically, this is incorrect since DW_OP_const <const>
-  // actually describes a value at a constant addess, not a constant value.
-  // However, in the past there was no better way  to describe a constant
-  // value, so the producers and consumers started to rely on heuristics
-  // to disambiguate the value vs. location status of the expression.
-  // See PR21176 for more details.
-  if (DwarfVersion >= 4)
-    EmitOp(dwarf::DW_OP_stack_value);
+  AddStackValue();
 }
 
 void DwarfExpression::AddUnsignedConstant(unsigned Value) {
   EmitOp(dwarf::DW_OP_constu);
   EmitUnsigned(Value);
-  // cf. comment in DwarfExpression::AddSignedConstant().
-  if (DwarfVersion >= 4)
-    EmitOp(dwarf::DW_OP_stack_value);
+  AddStackValue();
+}
+
+void DwarfExpression::AddUnsignedConstant(APInt Value) {
+  unsigned Size = Value.getBitWidth();
+  const uint64_t *Data = Value.getRawData();
+
+  // Chop it up into 64-bit pieces, because that's the maximum that
+  // AddUnsignedConstant takes.
+  unsigned Offset = 0;
+  while (Offset < Size) {
+    AddUnsignedConstant(*Data++);
+    if (Offset == 0 && Size <= 64)
+      break;
+    AddOpPiece(std::min(Size-Offset, 64u), Offset);
+    Offset += 64;
+  }
 }
 
 static unsigned getOffsetOrZero(unsigned OffsetInBits,