Skip to content

add visit_operand to const prop #74507

New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Merged
merged 3 commits into from
Jul 24, 2020
Merged

add visit_operand to const prop #74507

Show file tree
Hide file tree
Changes from 2 commits
Commits
Show all changes
3 commits
Select commit Hold shift + click to select a range
c74c648
const prop into operands
lcnr Jul 22, 2020
d257bac
note LLVM in fixme
lcnr Jul 22, 2020
61a9ab8
slightly adapt const prop
lcnr Jul 23, 2020
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
112 changes: 50 additions & 62 deletions src/librustc_mir/transform/const_prop.rs
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -582,6 +582,34 @@ impl<'mir, 'tcx> ConstPropagator<'mir, 'tcx> {
Some(())
}

fn propagate_operand(&mut self, operand: &mut Operand<'tcx>, location: Location) {
match *operand {
Operand::Copy(l) | Operand::Move(l) => {
if let Some(value) = self.get_const(l) {
if self.should_const_prop(value) {
// FIXME(felix91gr): this code only handles `Scalar` cases.
// For now, we're not handling `ScalarPair` cases because
// doing so here would require a lot of code duplication.
// We should hopefully generalize `Operand` handling into a fn,
// and use it to do const-prop here and everywhere else
// where it makes sense.
if let interpret::Operand::Immediate(interpret::Immediate::Scalar(
ScalarMaybeUninit::Scalar(scalar),
)) = *value
{
*operand = self.operand_from_scalar(
scalar,
value.layout.ty,
self.source_info.unwrap().span,
);
}
}
}
}
Operand::Constant(ref mut ct) => self.visit_constant(ct, location),
}
}

fn const_prop(
&mut self,
rvalue: &Rvalue<'tcx>,
Expand Down Expand Up @@ -905,6 +933,16 @@ impl<'mir, 'tcx> MutVisitor<'tcx> for ConstPropagator<'mir, 'tcx> {
}
}

fn visit_operand(&mut self, operand: &mut Operand<'tcx>, location: Location) {
// Only const prop copies and moves on `mir_opt_level=3` as doing so
// currently increases compile time.
if self.tcx.sess.opts.debugging_opts.mir_opt_level < 3 {
self.super_operand(operand, location)
} else {
self.propagate_operand(operand, location)
}
}

fn visit_constant(&mut self, constant: &mut Constant<'tcx>, location: Location) {
trace!("visit_constant: {:?}", constant);
self.super_constant(constant, location);
Expand Down Expand Up @@ -1072,18 +1110,13 @@ impl<'mir, 'tcx> MutVisitor<'tcx> for ConstPropagator<'mir, 'tcx> {
}
}
}
TerminatorKind::SwitchInt { ref mut discr, switch_ty, .. } => {
if let Some(value) = self.eval_operand(&discr, source_info) {
if self.should_const_prop(value) {
if let ScalarMaybeUninit::Scalar(scalar) =
self.ecx.read_scalar(value).unwrap()
{
*discr = self.operand_from_scalar(scalar, switch_ty, source_info.span);
}
}
}
TerminatorKind::SwitchInt { ref mut discr, .. } => {
// FIXME: This is currently redundant with `visit_operand`, but sadly
// always visiting operands currently causes a perf regression in LLVM codegen, so
// `visit_operand` currently only runs for propagates places for `mir_opt_level=3`.
self.propagate_operand(discr, location)
}
// None of these have Operands to const-propagate
// None of these have Operands to const-propagate.
TerminatorKind::Goto { .. }
| TerminatorKind::Resume
| TerminatorKind::Abort
Expand All @@ -1096,61 +1129,16 @@ impl<'mir, 'tcx> MutVisitor<'tcx> for ConstPropagator<'mir, 'tcx> {
| TerminatorKind::FalseEdge { .. }
| TerminatorKind::FalseUnwind { .. }
| TerminatorKind::InlineAsm { .. } => {}
// Every argument in our function calls can be const propagated.
TerminatorKind::Call { ref mut args, .. } => {
let mir_opt_level = self.tcx.sess.opts.debugging_opts.mir_opt_level;
// Constant Propagation into function call arguments is gated
// under mir-opt-level 2, because LLVM codegen gives performance
// regressions with it.
if mir_opt_level >= 2 {
for opr in args {
/*
The following code would appear to be incomplete, because
the function `Operand::place()` returns `None` if the
`Operand` is of the variant `Operand::Constant`. In this
context however, that variant will never appear. This is why:

When constructing the MIR, all function call arguments are
copied into `Locals` of `LocalKind::Temp`. At least, all arguments
that are not unsized (Less than 0.1% are unsized. See #71170
to learn more about those).

This means that, conversely, all `Operands` found as function call
arguments are of the variant `Operand::Copy`. This allows us to
simplify our handling of `Operands` in this case.
*/
if let Some(l) = opr.place() {
if let Some(value) = self.get_const(l) {
if self.should_const_prop(value) {
// FIXME(felix91gr): this code only handles `Scalar` cases.
// For now, we're not handling `ScalarPair` cases because
// doing so here would require a lot of code duplication.
// We should hopefully generalize `Operand` handling into a fn,
// and use it to do const-prop here and everywhere else
// where it makes sense.
if let interpret::Operand::Immediate(
interpret::Immediate::Scalar(ScalarMaybeUninit::Scalar(
scalar,
)),
) = *value
{
*opr = self.operand_from_scalar(
scalar,
value.layout.ty,
source_info.span,
);
}
}
}
}
}
}
}
// Every argument in our function calls have already been propagated in `visit_operand`.
//
// NOTE: because LLVM codegen gives performance regressions with it, so this is gated
// on `mir_opt_level=3`.
TerminatorKind::Call { .. } => {}
}

// We remove all Locals which are restricted in propagation to their containing blocks and
// which were modified in the current block.
// Take it out of the ecx so we can get a mutable reference to the ecx for `remove_const`
// Take it out of the ecx so we can get a mutable reference to the ecx for `remove_const`.
let mut locals = std::mem::take(&mut self.ecx.machine.written_only_inside_own_block_locals);
for &local in locals.iter() {
Self::remove_const(&mut self.ecx, local);
Expand Down
14 changes: 13 additions & 1 deletion src/test/mir-opt/const_prop/array_index/32bit/rustc.main.ConstProp.diff
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -64,13 +64,25 @@
+ // mir::Constant
+ // + span: $DIR/array_index.rs:5:18: 5:33
+ // + literal: Const { ty: bool, val: Value(Scalar(0x01)) }
+ assert(const true, "index out of bounds: the len is {} but the index is {}", move _4, _3) -> bb1; // scope 0 at $DIR/array_index.rs:5:18: 5:33
+ assert(const true, "index out of bounds: the len is {} but the index is {}", const 4_usize, const 2_usize) -> bb1; // scope 0 at $DIR/array_index.rs:5:18: 5:33
+ // ty::Const
+ // + ty: bool
+ // + val: Value(Scalar(0x01))
+ // mir::Constant
+ // + span: $DIR/array_index.rs:5:18: 5:33
+ // + literal: Const { ty: bool, val: Value(Scalar(0x01)) }
+ // ty::Const
+ // + ty: usize
+ // + val: Value(Scalar(0x00000004))
+ // mir::Constant
+ // + span: $DIR/array_index.rs:5:18: 5:33
+ // + literal: Const { ty: usize, val: Value(Scalar(0x00000004)) }
+ // ty::Const
+ // + ty: usize
+ // + val: Value(Scalar(0x00000002))
+ // mir::Constant
+ // + span: $DIR/array_index.rs:5:18: 5:33
+ // + literal: Const { ty: usize, val: Value(Scalar(0x00000002)) }
Copy link
Contributor

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

oh god these comments are really annoying 😆

Copy link
Contributor

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

i really wish there rwas a way to suppress all the comments in MIR dumps

Copy link
Contributor

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

#74508

}

bb1: {
Expand Down
14 changes: 13 additions & 1 deletion src/test/mir-opt/const_prop/array_index/64bit/rustc.main.ConstProp.diff
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -64,13 +64,25 @@
+ // mir::Constant
+ // + span: $DIR/array_index.rs:5:18: 5:33
+ // + literal: Const { ty: bool, val: Value(Scalar(0x01)) }
+ assert(const true, "index out of bounds: the len is {} but the index is {}", move _4, _3) -> bb1; // scope 0 at $DIR/array_index.rs:5:18: 5:33
+ assert(const true, "index out of bounds: the len is {} but the index is {}", const 4_usize, const 2_usize) -> bb1; // scope 0 at $DIR/array_index.rs:5:18: 5:33
+ // ty::Const
+ // + ty: bool
+ // + val: Value(Scalar(0x01))
+ // mir::Constant
+ // + span: $DIR/array_index.rs:5:18: 5:33
+ // + literal: Const { ty: bool, val: Value(Scalar(0x01)) }
+ // ty::Const
+ // + ty: usize
+ // + val: Value(Scalar(0x0000000000000004))
+ // mir::Constant
+ // + span: $DIR/array_index.rs:5:18: 5:33
+ // + literal: Const { ty: usize, val: Value(Scalar(0x0000000000000004)) }
+ // ty::Const
+ // + ty: usize
+ // + val: Value(Scalar(0x0000000000000002))
+ // mir::Constant
+ // + span: $DIR/array_index.rs:5:18: 5:33
+ // + literal: Const { ty: usize, val: Value(Scalar(0x0000000000000002)) }
}

bb1: {
Expand Down
32 changes: 26 additions & 6 deletions src/test/mir-opt/const_prop/bad_op_div_by_zero/rustc.main.ConstProp.diff
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -38,15 +38,22 @@
- // + span: $DIR/bad_op_div_by_zero.rs:5:14: 5:19
+ // + span: $DIR/bad_op_div_by_zero.rs:5:18: 5:19
// + literal: Const { ty: i32, val: Value(Scalar(0x00000000)) }
- assert(!move _4, "attempt to divide {} by zero", const 1_i32) -> bb1; // scope 1 at $DIR/bad_op_div_by_zero.rs:5:14: 5:19
+ _4 = const true; // scope 1 at $DIR/bad_op_div_by_zero.rs:5:14: 5:19
// ty::Const
+ // + ty: bool
+ // + val: Value(Scalar(0x01))
+ // mir::Constant
+ // + span: $DIR/bad_op_div_by_zero.rs:5:14: 5:19
+ // + literal: Const { ty: bool, val: Value(Scalar(0x01)) }
+ assert(!const true, "attempt to divide {} by zero", const 1_i32) -> bb1; // scope 1 at $DIR/bad_op_div_by_zero.rs:5:14: 5:19
+ // ty::Const
+ // + ty: bool
+ // + val: Value(Scalar(0x01))
+ // mir::Constant
+ // + span: $DIR/bad_op_div_by_zero.rs:5:14: 5:19
+ // + literal: Const { ty: bool, val: Value(Scalar(0x01)) }
assert(!move _4, "attempt to divide {} by zero", const 1_i32) -> bb1; // scope 1 at $DIR/bad_op_div_by_zero.rs:5:14: 5:19
// ty::Const
+ // ty::Const
// + ty: i32
// + val: Value(Scalar(0x00000001))
// mir::Constant
Expand Down Expand Up @@ -90,29 +97,42 @@
- _7 = BitAnd(move _5, move _6); // scope 1 at $DIR/bad_op_div_by_zero.rs:5:14: 5:19
- assert(!move _7, "attempt to compute `{} / {}` which would overflow", const 1_i32, _3) -> bb2; // scope 1 at $DIR/bad_op_div_by_zero.rs:5:14: 5:19
+ // + literal: Const { ty: bool, val: Value(Scalar(0x00)) }
+ assert(!const false, "attempt to compute `{} / {}` which would overflow", const 1_i32, _3) -> bb2; // scope 1 at $DIR/bad_op_div_by_zero.rs:5:14: 5:19
+ // ty::Const
+ assert(!const false, "attempt to compute `{} / {}` which would overflow", const 1_i32, const 0_i32) -> bb2; // scope 1 at $DIR/bad_op_div_by_zero.rs:5:14: 5:19
// ty::Const
+ // + ty: bool
+ // + val: Value(Scalar(0x00))
+ // mir::Constant
+ // + span: $DIR/bad_op_div_by_zero.rs:5:14: 5:19
+ // + literal: Const { ty: bool, val: Value(Scalar(0x00)) }
// ty::Const
+ // ty::Const
// + ty: i32
// + val: Value(Scalar(0x00000001))
// mir::Constant
// + span: $DIR/bad_op_div_by_zero.rs:5:14: 5:15
// + literal: Const { ty: i32, val: Value(Scalar(0x00000001)) }
+ // ty::Const
+ // + ty: i32
+ // + val: Value(Scalar(0x00000000))
+ // mir::Constant
+ // + span: $DIR/bad_op_div_by_zero.rs:5:14: 5:19
+ // + literal: Const { ty: i32, val: Value(Scalar(0x00000000)) }
}

bb2: {
_2 = Div(const 1_i32, move _3); // scope 1 at $DIR/bad_op_div_by_zero.rs:5:14: 5:19
- _2 = Div(const 1_i32, move _3); // scope 1 at $DIR/bad_op_div_by_zero.rs:5:14: 5:19
+ _2 = Div(const 1_i32, const 0_i32); // scope 1 at $DIR/bad_op_div_by_zero.rs:5:14: 5:19
// ty::Const
// + ty: i32
// + val: Value(Scalar(0x00000001))
// mir::Constant
// + span: $DIR/bad_op_div_by_zero.rs:5:14: 5:15
// + literal: Const { ty: i32, val: Value(Scalar(0x00000001)) }
+ // ty::Const
+ // + ty: i32
+ // + val: Value(Scalar(0x00000000))
+ // mir::Constant
+ // + span: $DIR/bad_op_div_by_zero.rs:5:14: 5:19
+ // + literal: Const { ty: i32, val: Value(Scalar(0x00000000)) }
StorageDead(_3); // scope 1 at $DIR/bad_op_div_by_zero.rs:5:18: 5:19
_0 = const (); // scope 0 at $DIR/bad_op_div_by_zero.rs:3:11: 6:2
// ty::Const
Expand Down
Loading