Enable const prop to also evaluate constants, not just literals
This commit is contained in:
Oliver Schneider
parent
4caf6a92f3
commit
f14e746b2f
@ -11,7 +11,7 @@
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//! Performs various peephole optimizations.
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use rustc::mir::{Constant, Literal, Location, Place, Mir, Operand, ProjectionElem, Rvalue, Local};
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use rustc::mir::{NullOp, StatementKind, Statement, BasicBlock};
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use rustc::mir::{NullOp, StatementKind, Statement, BasicBlock, LocalKind};
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use rustc::mir::{SourceInfo, ARGUMENT_VISIBILITY_SCOPE, TerminatorKind};
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use rustc::mir::visit::{MutVisitor, Visitor, TyContext};
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use rustc::middle::const_val::ConstVal;
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@ -34,6 +34,7 @@ impl MirPass for InstCombine {
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tcx: TyCtxt<'a, 'tcx, 'tcx>,
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source: MirSource,
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mir: &mut Mir<'tcx>) {
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trace!("InstCombine starting for {:?}", source.def_id);
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// First, find optimization opportunities. This is done in a pre-pass to keep the MIR
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// read-only so that we can do global analyses on the MIR in the process (e.g.
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@ -46,6 +47,7 @@ impl MirPass for InstCombine {
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// Then carry out those optimizations.
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MutVisitor::visit_mir(&mut InstCombineVisitor { optimizations, tcx }, mir);
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trace!("InstCombine done for {:?}", source.def_id);
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}
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}
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@ -199,7 +201,6 @@ impl<'b, 'a, 'tcx:'b> OptimizationFinder<'b, 'a, 'tcx> {
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ConstVal::Value(v) => Some((v, value.ty, c.span)),
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ConstVal::Unevaluated(did, substs) => {
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let param_env = self.tcx.param_env(self.source.def_id);
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let span = self.tcx.def_span(did);
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let instance = Instance::resolve(
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self.tcx,
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param_env,
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@ -211,7 +212,7 @@ impl<'b, 'a, 'tcx:'b> OptimizationFinder<'b, 'a, 'tcx> {
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promoted: None,
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};
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let (value, _, ty) = eval_body(self.tcx, cid, param_env)?;
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let val = (value, ty, span);
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let val = (value, ty, c.span);
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trace!("evaluated {:?} to {:?}", c, val);
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self.optimizations.constants.insert(c.clone(), val);
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Some(val)
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@ -269,7 +270,24 @@ impl<'b, 'a, 'tcx:'b> OptimizationFinder<'b, 'a, 'tcx> {
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span: Span,
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) -> Option<Const<'tcx>> {
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match *rvalue {
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Rvalue::Use(ref op) => self.simplify_operand(op),
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// No need to overwrite an already evaluated constant
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Rvalue::Use(Operand::Constant(box Constant {
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literal: Literal::Value {
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value: &ty::Const {
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val: ConstVal::Value(_),
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..
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},
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},
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..
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})) => None,
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// This branch exists for the sanity type check
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Rvalue::Use(Operand::Constant(ref c)) => {
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assert_eq!(c.ty, place_ty);
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self.eval_constant(c)
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},
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Rvalue::Use(ref op) => {
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self.eval_operand(op)
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},
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Rvalue::Repeat(..) |
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Rvalue::Ref(..) |
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Rvalue::Cast(..) |
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@ -392,6 +410,17 @@ impl ConstPropVisitor {
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cpv.visit_mir(mir);
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cpv.can_const_prop
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}
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fn is_our_local(&mut self, mut place: &Place) -> bool {
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while let Place::Projection(ref proj) = place {
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place = &proj.base;
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}
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if let Place::Local(local) = *place {
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local == self.local
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} else {
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false
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}
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}
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}
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impl<'tcx> Visitor<'tcx> for ConstPropVisitor {
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@ -403,9 +432,9 @@ impl<'tcx> Visitor<'tcx> for ConstPropVisitor {
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) {
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self.super_statement(block, statement, location);
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match statement.kind {
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StatementKind::SetDiscriminant { place: Place::Local(local), .. } |
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StatementKind::Assign(Place::Local(local), _) => {
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if local == self.local {
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StatementKind::SetDiscriminant { ref place, .. } |
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StatementKind::Assign(ref place, _) => {
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if self.is_our_local(place) {
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if self.found_assignment {
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self.can_const_prop = false;
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} else {
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@ -415,15 +444,13 @@ impl<'tcx> Visitor<'tcx> for ConstPropVisitor {
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},
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StatementKind::InlineAsm { ref outputs, .. } => {
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for place in outputs {
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if let Place::Local(local) = *place {
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if local == self.local {
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if self.found_assignment {
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self.can_const_prop = false;
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} else {
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self.found_assignment = true
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}
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return;
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if self.is_our_local(place) {
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if self.found_assignment {
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self.can_const_prop = false;
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} else {
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self.found_assignment = true
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}
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return;
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}
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}
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}
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@ -432,8 +459,8 @@ impl<'tcx> Visitor<'tcx> for ConstPropVisitor {
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}
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fn visit_rvalue(&mut self, rvalue: &Rvalue<'tcx>, location: Location) {
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self.super_rvalue(rvalue, location);
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if let Rvalue::Ref(_, _, Place::Local(local)) = *rvalue {
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if local == self.local {
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if let Rvalue::Ref(_, _, ref place) = *rvalue {
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if self.is_our_local(place) {
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self.can_const_prop = false;
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}
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}
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@ -517,12 +544,13 @@ impl<'b, 'a, 'tcx> Visitor<'tcx> for OptimizationFinder<'b, 'a, 'tcx> {
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if let Some(value) = self.const_prop(rval, place_ty, span) {
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self.optimizations.const_prop.insert(location, value);
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if let Place::Local(local) = *place {
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if !self.mir.local_decls[local].is_user_variable
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if self.mir.local_kind(local) == LocalKind::Temp
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&& ConstPropVisitor::check(local, self.mir) {
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trace!("storing {:?} to {:?}", value, local);
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assert!(self.optimizations.places.insert(local, value).is_none());
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}
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}
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return;
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}
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}
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self.super_statement(block, statement, location);
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