[DebugInfo] Introduce DW_OP_LLVM_convert

Introduce a DW_OP_LLVM_convert Dwarf expression pseudo op that allows
for a convenient way to perform type conversions on the Dwarf expression
stack. As an additional bonus it paves the way for using other Dwarf
v5 ops that need to reference a base_type.

The new DW_OP_LLVM_convert is used from lib/Transforms/Utils/Local.cpp
to perform sext/zext on debug values but mainly the patch is about
preparing terrain for adding other Dwarf v5 ops that need to reference a
base_type.

For Dwarf v5 the op maps to DW_OP_convert and for earlier versions a
complex shift & mask pattern is generated to emulate sext/zext.

Differential Revision: https://reviews.llvm.org/D56587

llvm-svn: 356442

1 files changed, 7 insertions, 2 deletions

diff --git a/llvm/lib/IR/AsmWriter.cpp b/llvm/lib/IR/AsmWriter.cpp
index af3db5186a2..07dea403d56 100644
--- a/llvm/lib/IR/AsmWriter.cpp
+++ b/llvm/lib/IR/AsmWriter.cpp
@@ -2123,8 +2123,13 @@ static void writeDIExpression(raw_ostream &Out, const DIExpression *N,
       assert(!OpStr.empty() && "Expected valid opcode");
 
       Out << FS << OpStr;
-      for (unsigned A = 0, AE = I->getNumArgs(); A != AE; ++A)
-        Out << FS << I->getArg(A);
+      if (I->getOp() == dwarf::DW_OP_LLVM_convert) {
+        Out << FS << I->getArg(0);
+        Out << FS << dwarf::AttributeEncodingString(I->getArg(1));
+      } else {
+        for (unsigned A = 0, AE = I->getNumArgs(); A != AE; ++A)
+          Out << FS << I->getArg(A);
+      }
     }
   } else {
     for (const auto &I : N->getElements())