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[DebugInfo] Corrections for salvageDebugInfo

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Summary:
When salvaging a dbg.declare/dbg.addr we should not add
DW_OP_stack_value to the DIExpression
(see test/Transforms/InstCombine/salvage-dbg-declare.ll).

Consider this example
  %vla = alloca i32, i64 2
  call void @llvm.dbg.declare(metadata i32* %vla, metadata !1, metadata !DIExpression())

Instcombine will turn it into
  %vla1 = alloca [2 x i32]
  %vla1.sub = getelementptr inbounds [2 x i32], [2 x i32]* %vla, i64 0, i64 0
  call void @llvm.dbg.declare(metadata [2 x i32]* %vla1.sub, metadata !19, metadata !DIExpression())

If the GEP can be eliminated, then the dbg.declare will be salvaged
and we should get
  %vla1 = alloca [2 x i32]
  call void @llvm.dbg.declare(metadata [2 x i32]* %vla1, metadata !19, metadata !DIExpression())

The problem was that salvageDebugInfo did not recognize dbg.declare
as being indirect (%vla1 points to the value, it does not hold the
value), so we incorrectly got
  call void @llvm.dbg.declare(metadata [2 x i32]* %vla1, metadata !19, metadata !DIExpression(DW_OP_stack_value))

I also made sure that llvm::salvageDebugInfo and
DIExpression::prependOpcodes do not add DW_OP_stack_value to
the DIExpression in case no new operands are added to the
DIExpression. That way we avoid to, unneccessarily, turn a
register location expression into an implicit location expression
in some situations (see test11 in test/Transforms/LICM/sinking.ll).

Reviewers: aprantl, vsk

Reviewed By: aprantl, vsk

Subscribers: JDevlieghere, llvm-commits

Differential Revision: https://reviews.llvm.org/D48837

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@336191 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Bjorn Pettersson
2018-07-03 11:29:00 +00:00
parent d5d94ca3a7
commit 13e9d31258
4 changed files with 68 additions and 4 deletions
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lib/IR/DebugInfoMetadata.cpp
+3
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@@ -803,6 +803,9 @@ DIExpression *DIExpression::prepend(const DIExpression *Expr, bool DerefBefore,
DIExpression *DIExpression::prependOpcodes(const DIExpression *Expr,
SmallVectorImpl<uint64_t> &Ops,
bool StackValue) {
// If there are no ops to prepend, do not even add the DW_OP_stack_value.
if (Ops.empty())
StackValue = false;
if (Expr)
for (auto Op : Expr->expr_ops()) {
// A DW_OP_stack_value comes at the end, but before a DW_OP_LLVM_fragment.