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Fix debug information for function arguments of type &str or slice. #81898

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Feb 18, 2021
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Fix debug information for function arguments of type &str or slice. #81898

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30 changes: 25 additions & 5 deletions compiler/rustc_codegen_ssa/src/mir/debuginfo.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -320,6 +320,8 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
) -> Option<IndexVec<mir::Local, Vec<PerLocalVarDebugInfo<'tcx, Bx::DIVariable>>>> {
let full_debug_info = self.cx.sess().opts.debuginfo == DebugInfo::Full;

let target_is_msvc = self.cx.sess().target.is_like_msvc;

if !full_debug_info && self.cx.sess().fewer_names() {
return None;
}
Expand All @@ -341,11 +343,29 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
&& var.source_info.scope == mir::OUTERMOST_SOURCE_SCOPE
{
let arg_index = place.local.index() - 1;

// FIXME(eddyb) shouldn't `ArgumentVariable` indices be
// offset in closures to account for the hidden environment?
// Also, is this `+ 1` needed at all?
VariableKind::ArgumentVariable(arg_index + 1)
if target_is_msvc {
// Rust compiler decomposes every &str or slice argument into two components:
// a pointer to the memory address where the data is stored and a usize representing
// the length of the str (or slice). These components will later be used to reconstruct
// the original argument inside the body of the function that owns it (see the
// definition of debug_introduce_local for more details).
//
// Since the original argument is declared inside a function rather than being passed
// in as an argument, it must be marked as a LocalVariable for MSVC debuggers to visualize
// its data correctly. (See issue #81894 for an in-depth description of the problem).
match *var_ty.kind() {
ty::Ref(_, inner_type, _) => match *inner_type.kind() {
ty::Slice(_) | ty::Str => VariableKind::LocalVariable,
_ => VariableKind::ArgumentVariable(arg_index + 1),
},
_ => VariableKind::ArgumentVariable(arg_index + 1),
}
} else {
// FIXME(eddyb) shouldn't `ArgumentVariable` indices be
// offset in closures to account for the hidden environment?
// Also, is this `+ 1` needed at all?
VariableKind::ArgumentVariable(arg_index + 1)
}
} else {
VariableKind::LocalVariable
};
Expand Down