[PATCH] D12134: Improve debug info for implicitly captured vars in lambdas

[David Blaikie via cfe-commits]

On Tue, Aug 18, 2015 at 9:05 PM, Alexey Bataev via cfe-commits <
cfe-commits at lists.llvm.org> wrote:

> ABataev created this revision.
> ABataev added reviewers: echristo, rjmccall, rsmith.
> ABataev added a subscriber: cfe-commits.
>
> When variables are implicitly captured in lambdas, debug info generated
> for captured variables points to location where they are used first.  This
> patch makes debug info to point to capture default location.
>

Not sure if this is the right tradeoff, or if it is, perhaps we should
reconsider how our diagnostics work too?

Currently if you, say, capture a variable by value and that variable
doesn't have an accessible copy ctor, the diagnostic points to the first
use. Should we change that too?


>
> http://reviews.llvm.org/D12134
>
> Files:
>   lib/Sema/SemaLambda.cpp
>   test/CodeGenCXX/debug-lambda-expressions.cpp
>
> Index: lib/Sema/SemaLambda.cpp
> ===================================================================
> --- lib/Sema/SemaLambda.cpp
> +++ lib/Sema/SemaLambda.cpp
> @@ -1377,10 +1377,10 @@
>  }
>
>  static ExprResult performLambdaVarCaptureInitialization(
> -    Sema &S, LambdaScopeInfo::Capture &Capture,
> -    FieldDecl *Field,
> +    Sema &S, LambdaScopeInfo::Capture &Capture, FieldDecl *Field,
>      SmallVectorImpl<VarDecl *> &ArrayIndexVars,
> -    SmallVectorImpl<unsigned> &ArrayIndexStarts) {
> +    SmallVectorImpl<unsigned> &ArrayIndexStarts, bool ImplicitCapture,
> +    SourceLocation CaptureDefaultLoc) {
>    assert(Capture.isVariableCapture() && "not a variable capture");
>
>    auto *Var = Capture.getVariable();
> @@ -1399,7 +1399,10 @@
>    //   An entity captured by a lambda-expression is odr-used (3.2) in
>    //   the scope containing the lambda-expression.
>    ExprResult RefResult = S.BuildDeclarationNameExpr(
> -      CXXScopeSpec(), DeclarationNameInfo(Var->getDeclName(), Loc), Var);
> +      CXXScopeSpec(),
> +      DeclarationNameInfo(Var->getDeclName(),
> +                          ImplicitCapture ? CaptureDefaultLoc : Loc),
> +      Var);
>    if (RefResult.isInvalid())
>      return ExprError();
>    Expr *Ref = RefResult.get();
> @@ -1561,7 +1564,8 @@
>        Expr *Init = From.getInitExpr();
>        if (!Init) {
>          auto InitResult = performLambdaVarCaptureInitialization(
> -            *this, From, *CurField, ArrayIndexVars, ArrayIndexStarts);
> +            *this, From, *CurField, ArrayIndexVars, ArrayIndexStarts,
> +            CaptureDefault != LCD_None, CaptureDefaultLoc);
>          if (InitResult.isInvalid())
>            return ExprError();
>          Init = InitResult.get();
> Index: test/CodeGenCXX/debug-lambda-expressions.cpp
> ===================================================================
> --- test/CodeGenCXX/debug-lambda-expressions.cpp
> +++ test/CodeGenCXX/debug-lambda-expressions.cpp
> @@ -14,6 +14,19 @@
>  struct D { D(); D(const D&); int x; };
>  int d(int x) { D y[10]; return [x,y] { return y[x].x; }(); }
>
> +// CHECK-LABEL: foo
> +int foo(int x) {
> +// CHECK: [[X:%.+]] = alloca i32,
> +// CHECK: call void @llvm.dbg.declare(
> +// CHECK: [[X_REF:%.+]] = getelementptr inbounds %{{.+}}, %{{.+}}*
> %{{.+}}, i32 0, i32 0, !dbg ![[DBG_FOO:[0-9]+]]
> +// CHECK: [[X_VAL:%.+]] = load i32, i32* [[X]], align 4, !dbg ![[DBG_FOO]]
> +// CHECK: store i32 [[X_VAL]], i32* [[X_REF]], align 4, !dbg ![[DBG_FOO]]
> +// CHECK: call i32 @{{.+}}, !dbg ![[DBG_FOO]]
> +  return [=] {
> +    return x;
> +  }();
> +}
> +
>  // Randomness for file. -- 6
>  // CHECK: [[FILE:.*]] = !DIFile(filename:
> "{{.*}}debug-lambda-expressions.cpp",
>
> @@ -100,3 +113,5 @@
>  // CHECK-SAME:                          line: [[VAR_LINE]],
>  // CHECK-SAME:                          elements: ![[VAR_ARGS:[0-9]+]]
>  // CHECK: ![[VAR_ARGS]] = !{!{{[0-9]+}}}
> +
> +// CHECK: [[DBG_FOO:![0-9]+]] = !DILocation(line: 25,
>
>
>
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