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Remove dead code from LocalAnalyzer #85965

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merged 2 commits into from
Jun 7, 2021
Merged

Remove dead code from LocalAnalyzer #85965

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59b6583
Remove unused support for `VarDebugInfo`
tmiasko Jun 2, 2021
624c693
Remove check for projections in a branch without any
tmiasko Jun 3, 2021
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50 changes: 4 additions & 46 deletions compiler/rustc_codegen_ssa/src/mir/analyze.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -7,9 +7,7 @@ use rustc_data_structures::graph::dominators::Dominators;
use rustc_index::bit_set::BitSet;
use rustc_index::vec::{Idx, IndexVec};
use rustc_middle::mir::traversal;
use rustc_middle::mir::visit::{
MutatingUseContext, NonMutatingUseContext, NonUseContext, PlaceContext, Visitor,
};
use rustc_middle::mir::visit::{MutatingUseContext, NonMutatingUseContext, PlaceContext, Visitor};
use rustc_middle::mir::{self, Location, TerminatorKind};
use rustc_middle::ty;
use rustc_middle::ty::layout::HasTyCtxt;
Expand All @@ -21,7 +19,9 @@ pub fn non_ssa_locals<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>>(
let mir = fx.mir;
let mut analyzer = LocalAnalyzer::new(fx);

analyzer.visit_body(&mir);
for (bb, data) in mir.basic_blocks().iter_enumerated() {
analyzer.visit_basic_block_data(bb, data);
}

for (local, decl) in mir.local_decls.iter_enumerated() {
let ty = fx.monomorphize(decl.ty);
Expand Down Expand Up @@ -142,36 +142,7 @@ impl<Bx: BuilderMethods<'a, 'tcx>> LocalAnalyzer<'mir, 'a, 'tcx, Bx> {

if let mir::ProjectionElem::Deref = elem {
// Deref projections typically only read the pointer.
// (the exception being `VarDebugInfo` contexts, handled below)
base_context = PlaceContext::NonMutatingUse(NonMutatingUseContext::Copy);

// Indirect debuginfo requires going through memory, that only
// the debugger accesses, following our emitted DWARF pointer ops.
//
// FIXME(eddyb) Investigate the possibility of relaxing this, but
// note that `llvm.dbg.declare` *must* be used for indirect places,
// even if we start using `llvm.dbg.value` for all other cases,
// as we don't necessarily know when the value changes, but only
// where it lives in memory.
//
// It's possible `llvm.dbg.declare` could support starting from
// a pointer that doesn't point to an `alloca`, but this would
// only be useful if we know the pointer being `Deref`'d comes
// from an immutable place, and if `llvm.dbg.declare` calls
// must be at the very start of the function, then only function
// arguments could contain such pointers.
if context == PlaceContext::NonUse(NonUseContext::VarDebugInfo) {
// We use `NonUseContext::VarDebugInfo` for the base,
// which might not force the base local to memory,
// so we have to do it manually.
self.visit_local(&place_ref.local, context, location);
}
}

// `NonUseContext::VarDebugInfo` needs to flow all the
// way down to the base local (see `visit_local`).
if context == PlaceContext::NonUse(NonUseContext::VarDebugInfo) {
base_context = context;
}

self.process_place(&place_base, base_context, location);
Expand All @@ -186,20 +157,7 @@ impl<Bx: BuilderMethods<'a, 'tcx>> LocalAnalyzer<'mir, 'a, 'tcx, Bx> {
);
}
} else {
// FIXME this is super_place code, is repeated here to avoid cloning place or changing
// visit_place API
let mut context = context;

if !place_ref.projection.is_empty() {
context = if context.is_mutating_use() {
PlaceContext::MutatingUse(MutatingUseContext::Projection)
} else {
PlaceContext::NonMutatingUse(NonMutatingUseContext::Projection)
};
}

self.visit_local(&place_ref.local, context, location);
self.visit_projection(*place_ref, context, location);
}
}
}
Expand Down