Auto merge of #68961 - eddyb:dbg-stack-dunk, r=nagisa
rustc_codegen_ssa: only "spill" SSA-like values to the stack for debuginfo. This is an implementation of the idea described in https://github.com/rust-lang/rust/issues/68817#issuecomment-583719182. In short, instead of debuginfo forcing otherwise-SSA-like MIR locals into `alloca`s, and requiring a `load` for each use (or two, for scalar pairs), the `alloca` is now *only* used for attaching debuginfo with `llvm.dbg.declare`: the `OperandRef` is stored to the `alloca`, but *never loaded* from it. Outside of `debug_introduce_local`, nothing cares about the debuginfo-only `alloca`, and instead works with `OperandRef` the same as MIR locals without debuginfo before this PR. This should have some of the benefits of `llvm.dbg.value`, while working today. cc @nagisa @nikomatsakis
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commit
b6690a8c35
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@ -8,7 +8,6 @@ use rustc::mir::visit::{
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MutatingUseContext, NonMutatingUseContext, NonUseContext, PlaceContext, Visitor,
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};
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use rustc::mir::{self, Location, TerminatorKind};
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use rustc::session::config::DebugInfo;
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use rustc::ty;
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use rustc::ty::layout::{HasTyCtxt, LayoutOf};
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use rustc_data_structures::graph::dominators::Dominators;
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@ -24,15 +23,6 @@ pub fn non_ssa_locals<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>>(
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analyzer.visit_body(mir);
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for (local, decl) in mir.local_decls.iter_enumerated() {
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// FIXME(eddyb): We should figure out how to use llvm.dbg.value instead
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// of putting everything in allocas just so we can use llvm.dbg.declare.
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if fx.cx.sess().opts.debuginfo == DebugInfo::Full {
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if fx.mir.local_kind(local) == mir::LocalKind::Arg {
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analyzer.not_ssa(local);
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continue;
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}
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}
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let ty = fx.monomorphize(&decl.ty);
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debug!("local {:?} has type `{}`", local, ty);
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let layout = fx.cx.spanned_layout_of(ty, decl.source_info.span);
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@ -281,15 +271,6 @@ impl<'mir, 'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> Visitor<'tcx>
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self.assign(local, location);
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}
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PlaceContext::NonUse(NonUseContext::VarDebugInfo) => {
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// We need to keep locals in `alloca`s for debuginfo.
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// FIXME(eddyb): We should figure out how to use `llvm.dbg.value` instead
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// of putting everything in allocas just so we can use `llvm.dbg.declare`.
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if self.fx.cx.sess().opts.debuginfo == DebugInfo::Full {
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self.not_ssa(local);
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}
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}
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PlaceContext::NonUse(_) | PlaceContext::MutatingUse(MutatingUseContext::Retag) => {}
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PlaceContext::NonMutatingUse(NonMutatingUseContext::Copy)
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@ -1145,6 +1145,7 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
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let op = bx.load_operand(place);
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place.storage_dead(bx);
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self.locals[index] = LocalRef::Operand(Some(op));
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self.debug_introduce_local(bx, index);
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}
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LocalRef::Operand(Some(op)) => {
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assert!(op.layout.is_zst(), "assigning to initialized SSAtemp");
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@ -1186,6 +1187,7 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
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let op = bx.load_operand(tmp);
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tmp.storage_dead(bx);
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self.locals[index] = LocalRef::Operand(Some(op));
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self.debug_introduce_local(bx, index);
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}
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DirectOperand(index) => {
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// If there is a cast, we have to store and reload.
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@ -1200,6 +1202,7 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
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OperandRef::from_immediate_or_packed_pair(bx, llval, ret_abi.layout)
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};
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self.locals[index] = LocalRef::Operand(Some(op));
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self.debug_introduce_local(bx, index);
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}
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}
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}
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@ -9,7 +9,8 @@ use rustc_index::vec::IndexVec;
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use rustc_span::symbol::{kw, Symbol};
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use rustc_span::{BytePos, Span};
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use super::OperandValue;
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use super::operand::OperandValue;
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use super::place::PlaceRef;
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use super::{FunctionCx, LocalRef};
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pub struct FunctionDebugContext<D> {
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@ -111,8 +112,6 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
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/// Apply debuginfo and/or name, after creating the `alloca` for a local,
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/// or initializing the local with an operand (whichever applies).
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// FIXME(eddyb) use `llvm.dbg.value` (which would work for operands),
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// not just `llvm.dbg.declare` (which requires `alloca`).
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pub fn debug_introduce_local(&self, bx: &mut Bx, local: mir::Local) {
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let full_debug_info = bx.sess().opts.debuginfo == DebugInfo::Full;
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@ -180,38 +179,60 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
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let local_ref = &self.locals[local];
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if !bx.sess().fewer_names() {
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let name = match whole_local_var.or(fallback_var) {
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let name = if bx.sess().fewer_names() {
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None
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} else {
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Some(match whole_local_var.or(fallback_var) {
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Some(var) if var.name != kw::Invalid => var.name.to_string(),
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_ => format!("{:?}", local),
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};
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})
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};
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if let Some(name) = &name {
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match local_ref {
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LocalRef::Place(place) | LocalRef::UnsizedPlace(place) => {
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bx.set_var_name(place.llval, &name);
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bx.set_var_name(place.llval, name);
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}
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LocalRef::Operand(Some(operand)) => match operand.val {
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OperandValue::Ref(x, ..) | OperandValue::Immediate(x) => {
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bx.set_var_name(x, &name);
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bx.set_var_name(x, name);
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}
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OperandValue::Pair(a, b) => {
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// FIXME(eddyb) these are scalar components,
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// maybe extract the high-level fields?
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bx.set_var_name(a, &(name.clone() + ".0"));
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bx.set_var_name(b, &(name + ".1"));
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bx.set_var_name(b, &(name.clone() + ".1"));
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}
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},
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LocalRef::Operand(None) => {}
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}
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}
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if !full_debug_info {
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if !full_debug_info || vars.is_empty() && fallback_var.is_none() {
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return;
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}
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// FIXME(eddyb) add debuginfo for unsized places too.
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let base = match local_ref {
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LocalRef::Place(place) => place,
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_ => return,
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LocalRef::Operand(None) => return,
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LocalRef::Operand(Some(operand)) => {
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// "Spill" the value onto the stack, for debuginfo,
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// without forcing non-debuginfo uses of the local
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// to also load from the stack every single time.
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// FIXME(#68817) use `llvm.dbg.value` instead,
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// at least for the cases which LLVM handles correctly.
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let spill_slot = PlaceRef::alloca(bx, operand.layout);
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if let Some(name) = name {
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bx.set_var_name(spill_slot.llval, &(name + ".dbg.spill"));
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}
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operand.val.store(bx, spill_slot);
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spill_slot
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}
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LocalRef::Place(place) => *place,
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// FIXME(eddyb) add debuginfo for unsized places too.
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LocalRef::UnsizedPlace(_) => return,
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};
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let vars = vars.iter().copied().chain(fallback_var);
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@ -1,5 +1,3 @@
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// ignore-tidy-linelength
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// compile-flags: -C no-prepopulate-passes
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#![crate_type = "lib"]
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@ -61,19 +59,19 @@ pub fn naked_recursive() {
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naked_empty();
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// CHECK-NEXT: %{{[0-9]+}} = call i{{[0-9]+}} @naked_with_return()
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// CHECK-NEXT: %_4 = call i{{[0-9]+}} @naked_with_return()
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// FIXME(#39685) Avoid one block per call.
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// CHECK-NEXT: br label %bb2
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// CHECK: bb2:
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// CHECK-NEXT: %{{[0-9]+}} = call i{{[0-9]+}} @naked_with_args_and_return(i{{[0-9]+}} %{{[0-9]+}})
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// CHECK-NEXT: %_3 = call i{{[0-9]+}} @naked_with_args_and_return(i{{[0-9]+}} %_4)
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// FIXME(#39685) Avoid one block per call.
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// CHECK-NEXT: br label %bb3
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// CHECK: bb3:
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// CHECK-NEXT: call void @naked_with_args(i{{[0-9]+}} %{{[0-9]+}})
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// CHECK-NEXT: call void @naked_with_args(i{{[0-9]+}} %_3)
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// FIXME(#39685) Avoid one block per call.
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// CHECK-NEXT: br label %bb4
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@ -6,7 +6,7 @@
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// gdb-command:run
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// gdb-command:next
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// gdb-check:[...]25[...]s
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// gdb-check:[...]24[...]let s = Some(5).unwrap(); // #break
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// gdb-command:continue
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#![feature(omit_gdb_pretty_printer_section)]
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