[PATCH] D12134: Improve debug info for implicitly captured vars in lambdas
Bataev, Alexey via cfe-commits
cfe-commits at lists.llvm.org
Tue Aug 25 10:50:53 PDT 2015
Guys, talking about implicitly captured variables we have to deal with 2
locations: 1) point of real capturing (it is the point of '=' or '&'
symbols in lambda capture-list); 2) a point of first use of variable
inside lambda's body.
When we're talking about diagnostic for implicitly captured variables we
have to deal with the second point, not the first one, because of
usability. I don't think that the "diagnostic consumer" would be happy
to see a message like "unnamed variable cannot be implicitly captured in
a lambda expression" pointing to '=' or '&'. Here we have to emit the
diagnostic at the point of the very first use of the variable we're
going to capture to make diagnostic more user-friendly. But actual point
of capturing is still a point, where we have '=' or '&' symbols in
capture-list.
Best regards,
Alexey Bataev
=============
Software Engineer
Intel Compiler Team
25.08.2015 19:00, Eric Christopher пишет:
>
> Yeah. I can't see a difference here being useful, and more likely harmful.
>
>
> On Tue, Aug 25, 2015, 8:48 AM David Blaikie <dblaikie at gmail.com
> <mailto:dblaikie at gmail.com>> wrote:
>
> On Tue, Aug 25, 2015 at 8:44 AM, Bataev, Alexey
> <a.bataev at hotmail.com <mailto:a.bataev at hotmail.com>> wrote:
>
> Debug info points to the real place where it is captured,
> while diagnostics points to the first use of implicitly
> captured variable.
>
>
> Right, but I'm trying to understand the justification for why
> that's the right thing to do. Why the debug info user would want a
> different experience than the compiler diagnostic consumer would want.
>
>
> - David
>
>
>
> Best regards,
> Alexey Bataev
> =============
> Software Engineer
> Intel Compiler Team
>
> 25.08.2015 18 <tel:25.08.2015%2018>:22, David Blaikie пишет:
>
>
>
> On Tue, Aug 25, 2015 at 8:18 AM, Bataev, Alexey
> <a.bataev at hotmail.com <mailto:a.bataev at hotmail.com>
> <mailto:a.bataev at hotmail.com
> <mailto:a.bataev at hotmail.com>>> wrote:
>
> I though about this. I think it will be more
> convenient for user
> to see the diagnostic on the first use of the variable
> rather than
> on '=' or '&' symbol.
>
>
> Why the difference between the diagnostic & the debug
> info, then?
>
>
> Best regards,
> Alexey Bataev
> =============
> Software Engineer
> Intel Compiler Team
>
> 25.08.2015 18 <tel:25.08.2015%2018>
> <tel:25.08.2015%2018>:07, David Blaikie пишет:
>
>
>
> On Tue, Aug 18, 2015 at 9:05 PM, Alexey Bataev via
> cfe-commits
> <cfe-commits at lists.llvm.org
> <mailto:cfe-commits at lists.llvm.org>
> <mailto:cfe-commits at lists.llvm.org
> <mailto:cfe-commits at lists.llvm.org>>
> <mailto:cfe-commits at lists.llvm.org
> <mailto:cfe-commits at lists.llvm.org>
>
> <mailto:cfe-commits at lists.llvm.org
> <mailto: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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