Align definition of DW_OP_plus with DWARF spec [1/3]

fhahn · fhahn · commit c9c403c0d471 · 2017-06-13T16:54:44.000Z
Summary: This patch is part of 3 patches that together form a single patch, but must be introduced in stages in order not to break things. The way that LLVM interprets DW_OP_plus in DIExpression nodes is basically that of the DW_OP_plus_uconst operator since LLVM expects an unsigned constant operand. This unnecessarily restricts the DW_OP_plus operator, preventing it from being used to describe the evaluation of runtime values on the expression stack. These patches try to align the semantics of DW_OP_plus and DW_OP_minus with that of the DWARF definition, which pops two elements off the expression stack, performs the operation and pushes the result back on the stack. This is done in three stages: • The first patch (LLVM) adds support for DW_OP_plus_uconst. • The second patch (Clang) contains changes all its uses from DW_OP_plus to DW_OP_plus_uconst. • The third patch (LLVM) changes the semantics of DW_OP_plus and DW_OP_minus to be in line with its DWARF meaning. This patch includes the bitcode upgrade from legacy DIExpressions. Patch by Sander de Smalen. Reviewers: pcc, echristo, aprantl Reviewed By: aprantl Subscribers: fhahn, aprantl, javed.absar, llvm-commits Differential Revision: https://reviews.llvm.org/D33892 llvm-svn: 305304
diff --git a/llvm/docs/LangRef.rst b/llvm/docs/LangRef.rst
@@ -4405,6 +4405,7 @@ The current supported vocabulary is limited:
 
 - ``DW_OP_deref`` dereferences the top of the expression stack.
 - ``DW_OP_plus, 93`` adds ``93`` to the working expression.
+- ``DW_OP_plus_uconst, 93`` adds ``93`` to the working expression.
 - ``DW_OP_LLVM_fragment, 16, 8`` specifies the offset and size (``16`` and ``8``
   here, respectively) of the variable fragment from the working expression. Note
   that contrary to DW_OP_bit_piece, the offset is describing the the location
@@ -4427,6 +4428,7 @@ combined with a concrete location.
 
     !0 = !DIExpression(DW_OP_deref)
     !1 = !DIExpression(DW_OP_plus, 3)
+    !1 = !DIExpression(DW_OP_plus_uconst, 3)
     !2 = !DIExpression(DW_OP_bit_piece, 3, 7)
     !3 = !DIExpression(DW_OP_deref, DW_OP_plus, 3, DW_OP_LLVM_fragment, 3, 7)
     !4 = !DIExpression(DW_OP_constu, 2, DW_OP_swap, DW_OP_xderef)
diff --git a/llvm/lib/CodeGen/AsmPrinter/DwarfExpression.cpp b/llvm/lib/CodeGen/AsmPrinter/DwarfExpression.cpp
@@ -248,6 +248,12 @@ bool DwarfExpression::addMachineRegExpression(const TargetRegisterInfo &TRI,
   assert(Reg.Size == 0 && "subregister has same size as superregister");
 
   // Pattern-match combinations for which more efficient representations exist.
+  // [Reg, DW_OP_plus_uconst, Offset] --> [DW_OP_breg, Offset].
+  if (Op && (Op->getOp() == dwarf::DW_OP_plus_uconst)) {
+    SignedOffset = Op->getArg(0);
+    ExprCursor.take();
+  }
+
   // [Reg, Offset, DW_OP_plus] --> [DW_OP_breg, Offset].
   // [Reg, Offset, DW_OP_minus] --> [DW_OP_breg, -Offset].
   // If Reg is a subregister we need to mask it out before subtracting.
@@ -321,6 +327,7 @@ void DwarfExpression::addExpression(DIExpressionCursor &&ExprCursor,
       return;
     }
     case dwarf::DW_OP_plus:
+    case dwarf::DW_OP_plus_uconst:
       assert(LocationKind != Register);
       emitOp(dwarf::DW_OP_plus_uconst);
       emitUnsigned(Op->getArg(0));
diff --git a/llvm/lib/IR/DebugInfoMetadata.cpp b/llvm/lib/IR/DebugInfoMetadata.cpp
@@ -599,6 +599,7 @@ unsigned DIExpression::ExprOperand::getSize() const {
     return 3;
   case dwarf::DW_OP_constu:
   case dwarf::DW_OP_plus:
+  case dwarf::DW_OP_plus_uconst:
   case dwarf::DW_OP_minus:
     return 2;
   default:
@@ -641,6 +642,7 @@ bool DIExpression::isValid() const {
       break;
     }
     case dwarf::DW_OP_constu:
+    case dwarf::DW_OP_plus_uconst:
     case dwarf::DW_OP_plus:
     case dwarf::DW_OP_minus:
     case dwarf::DW_OP_deref:
@@ -679,7 +681,8 @@ bool DIExpression::extractIfOffset(int64_t &Offset) const {
   }
   if (getNumElements() != 2)
     return false;
-  if (Elements[0] == dwarf::DW_OP_plus) {
+  if (Elements[0] == dwarf::DW_OP_plus ||
+      Elements[0] == dwarf::DW_OP_plus_uconst) {
     Offset = Elements[1];
     return true;
   }
diff --git a/llvm/test/Assembler/diexpression.ll b/llvm/test/Assembler/diexpression.ll
@@ -1,18 +1,20 @@
 ; RUN: llvm-as < %s | llvm-dis | llvm-as | llvm-dis | FileCheck %s
 ; RUN: verify-uselistorder %s
 
-; CHECK: !named = !{!0, !1, !2, !3, !4, !5}
-!named = !{!0, !1, !2, !3, !4, !5}
+; CHECK: !named = !{!0, !1, !2, !3, !4, !5, !6}
+!named = !{!0, !1, !2, !3, !4, !5, !6}
 
 ; CHECK:      !0 = !DIExpression()
 ; CHECK-NEXT: !1 = !DIExpression(DW_OP_deref)
 ; CHECK-NEXT: !2 = !DIExpression(DW_OP_plus, 3)
 ; CHECK-NEXT: !3 = !DIExpression(DW_OP_LLVM_fragment, 3, 7)
 ; CHECK-NEXT: !4 = !DIExpression(DW_OP_deref, DW_OP_plus, 3, DW_OP_LLVM_fragment, 3, 7)
 ; CHECK-NEXT: !5 = !DIExpression(DW_OP_constu, 2, DW_OP_swap, DW_OP_xderef)
+; CHECK-NEXT: !6 = !DIExpression(DW_OP_plus_uconst, 3)
 !0 = !DIExpression()
 !1 = !DIExpression(DW_OP_deref)
 !2 = !DIExpression(DW_OP_plus, 3)
 !3 = !DIExpression(DW_OP_LLVM_fragment, 3, 7)
 !4 = !DIExpression(DW_OP_deref, DW_OP_plus, 3, DW_OP_LLVM_fragment, 3, 7)
 !5 = !DIExpression(DW_OP_constu, 2, DW_OP_swap, DW_OP_xderef)
+!6 = !DIExpression(DW_OP_plus_uconst, 3)
diff --git a/llvm/unittests/IR/MetadataTest.cpp b/llvm/unittests/IR/MetadataTest.cpp
@@ -2043,6 +2043,7 @@ TEST_F(DIExpressionTest, isValid) {
 
   // Valid constructions.
   EXPECT_VALID(dwarf::DW_OP_plus, 6);
+  EXPECT_VALID(dwarf::DW_OP_plus_uconst, 6);
   EXPECT_VALID(dwarf::DW_OP_deref);
   EXPECT_VALID(dwarf::DW_OP_LLVM_fragment, 3, 7);
   EXPECT_VALID(dwarf::DW_OP_plus, 6, dwarf::DW_OP_deref);
@@ -2054,6 +2055,7 @@ TEST_F(DIExpressionTest, isValid) {
   // Invalid constructions.
   EXPECT_INVALID(~0u);
   EXPECT_INVALID(dwarf::DW_OP_plus);
+  EXPECT_INVALID(dwarf::DW_OP_plus_uconst);
   EXPECT_INVALID(dwarf::DW_OP_LLVM_fragment);
   EXPECT_INVALID(dwarf::DW_OP_LLVM_fragment, 3);
   EXPECT_INVALID(dwarf::DW_OP_LLVM_fragment, 3, 7, dwarf::DW_OP_plus, 3);
