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Unrolled build for rust-lang#115962
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Rollup merge of rust-lang#115962 - Zalathar:debug, r=oli-obk

coverage: Remove debug code from the instrumentor

The coverage instrumentor has an entire module full of complex code that is only used for debugging.

And as I continue to work on coverage, I keep finding that this debug code is constantly causing more trouble than it's worth. It's deeply entangled with current implementation details, such that making any non-trivial change to the instrumentor usually requires major changes to the debug code. And so far I have personally not found any of this debug code to be *useful*.

In light of that situation, I'd like to try just ripping all of it out. If I spend any more time dealing with coverage debug code, I want it to be because I'm writing new and useful tools, not dutifully maintaining a boat-anchor that quite plausibly isn't being used by anyone at all.

---
r? `@ghost`
`@rustbot` label +A-code-coverage

---

[Zulip thread](https://rust-lang.zulipchat.com/#narrow/stream/131828-t-compiler/topic/Removing.20debug.20code.20from.20the.20coverage.20instrumentor)
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@rust-timer
rust-timer authored Sep 20, 2023
2 parents e3811a7 + e015f5a commit 583f006
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Showing 9 changed files with 38 additions and 1,087 deletions.
101 changes: 26 additions & 75 deletions compiler/rustc_mir_transform/src/coverage/counters.rs
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Original file line number Diff line number Diff line change
@@ -1,10 +1,8 @@
use super::Error;

use super::debug;
use super::graph;
use super::spans;

use debug::{DebugCounters, NESTED_INDENT};
use graph::{BasicCoverageBlock, BcbBranch, CoverageGraph, TraverseCoverageGraphWithLoops};
use spans::CoverageSpan;

Expand All @@ -16,6 +14,8 @@ use rustc_middle::mir::coverage::*;

use std::fmt::{self, Debug};

const NESTED_INDENT: &str = " ";

/// The coverage counter or counter expression associated with a particular
/// BCB node or BCB edge.
#[derive(Clone)]
Expand Down Expand Up @@ -75,8 +75,6 @@ pub(super) struct CoverageCounters {
/// BCB/edge, but are needed as operands to more complex expressions.
/// These are always [`BcbCounter::Expression`].
pub(super) intermediate_expressions: Vec<BcbCounter>,

pub debug_counters: DebugCounters,
}

impl CoverageCounters {
Expand All @@ -91,17 +89,9 @@ impl CoverageCounters {
bcb_edge_counters: FxHashMap::default(),
bcb_has_incoming_edge_counters: BitSet::new_empty(num_bcbs),
intermediate_expressions: Vec::new(),

debug_counters: DebugCounters::new(),
}
}

/// Activate the `DebugCounters` data structures, to provide additional debug formatting
/// features when formatting [`BcbCounter`] (counter) values.
pub fn enable_debug(&mut self) {
self.debug_counters.enable();
}

/// Makes [`BcbCounter`] `Counter`s and `Expressions` for the `BasicCoverageBlock`s directly or
/// indirectly associated with `CoverageSpans`, and accumulates additional `Expression`s
/// representing intermediate values.
Expand All @@ -113,44 +103,18 @@ impl CoverageCounters {
MakeBcbCounters::new(self, basic_coverage_blocks).make_bcb_counters(coverage_spans)
}

fn make_counter<F>(&mut self, debug_block_label_fn: F) -> BcbCounter
where
F: Fn() -> Option<String>,
{
let counter = BcbCounter::Counter { id: self.next_counter() };
if self.debug_counters.is_enabled() {
self.debug_counters.add_counter(&counter, (debug_block_label_fn)());
}
counter
fn make_counter(&mut self) -> BcbCounter {
let id = self.next_counter();
BcbCounter::Counter { id }
}

fn make_expression<F>(
&mut self,
lhs: Operand,
op: Op,
rhs: Operand,
debug_block_label_fn: F,
) -> BcbCounter
where
F: Fn() -> Option<String>,
{
fn make_expression(&mut self, lhs: Operand, op: Op, rhs: Operand) -> BcbCounter {
let id = self.next_expression();
let expression = BcbCounter::Expression { id, lhs, op, rhs };
if self.debug_counters.is_enabled() {
self.debug_counters.add_counter(&expression, (debug_block_label_fn)());
}
expression
BcbCounter::Expression { id, lhs, op, rhs }
}

pub fn make_identity_counter(&mut self, counter_operand: Operand) -> BcbCounter {
let some_debug_block_label = if self.debug_counters.is_enabled() {
self.debug_counters.some_block_label(counter_operand).cloned()
} else {
None
};
self.make_expression(counter_operand, Op::Add, Operand::Zero, || {
some_debug_block_label.clone()
})
self.make_expression(counter_operand, Op::Add, Operand::Zero)
}

/// Counter IDs start from one and go up.
Expand Down Expand Up @@ -367,12 +331,8 @@ impl<'a> MakeBcbCounters<'a> {
branch_counter_operand,
Op::Add,
sumup_counter_operand,
|| None,
);
debug!(
" [new intermediate expression: {}]",
self.format_counter(&intermediate_expression)
);
debug!(" [new intermediate expression: {:?}]", intermediate_expression);
let intermediate_expression_operand = intermediate_expression.as_operand();
self.coverage_counters.intermediate_expressions.push(intermediate_expression);
some_sumup_counter_operand.replace(intermediate_expression_operand);
Expand All @@ -394,9 +354,8 @@ impl<'a> MakeBcbCounters<'a> {
branching_counter_operand,
Op::Subtract,
sumup_counter_operand,
|| Some(format!("{expression_branch:?}")),
);
debug!("{:?} gets an expression: {}", expression_branch, self.format_counter(&expression));
debug!("{:?} gets an expression: {:?}", expression_branch, expression);
let bcb = expression_branch.target_bcb;
if expression_branch.is_only_path_to_target() {
self.coverage_counters.set_bcb_counter(bcb, expression)?;
Expand All @@ -418,10 +377,10 @@ impl<'a> MakeBcbCounters<'a> {
// If the BCB already has a counter, return it.
if let Some(counter_kind) = &self.coverage_counters.bcb_counters[bcb] {
debug!(
"{}{:?} already has a counter: {}",
"{}{:?} already has a counter: {:?}",
NESTED_INDENT.repeat(debug_indent_level),
bcb,
self.format_counter(counter_kind),
counter_kind,
);
return Ok(counter_kind.as_operand());
}
Expand All @@ -431,22 +390,22 @@ impl<'a> MakeBcbCounters<'a> {
// program results in a tight infinite loop, but it should still compile.
let one_path_to_target = self.bcb_has_one_path_to_target(bcb);
if one_path_to_target || self.bcb_predecessors(bcb).contains(&bcb) {
let counter_kind = self.coverage_counters.make_counter(|| Some(format!("{bcb:?}")));
let counter_kind = self.coverage_counters.make_counter();
if one_path_to_target {
debug!(
"{}{:?} gets a new counter: {}",
"{}{:?} gets a new counter: {:?}",
NESTED_INDENT.repeat(debug_indent_level),
bcb,
self.format_counter(&counter_kind),
counter_kind,
);
} else {
debug!(
"{}{:?} has itself as its own predecessor. It can't be part of its own \
Expression sum, so it will get its own new counter: {}. (Note, the compiled \
Expression sum, so it will get its own new counter: {:?}. (Note, the compiled \
code will generate an infinite loop.)",
NESTED_INDENT.repeat(debug_indent_level),
bcb,
self.format_counter(&counter_kind),
counter_kind,
);
}
return self.coverage_counters.set_bcb_counter(bcb, counter_kind);
Expand Down Expand Up @@ -481,12 +440,11 @@ impl<'a> MakeBcbCounters<'a> {
sumup_edge_counter_operand,
Op::Add,
edge_counter_operand,
|| None,
);
debug!(
"{}new intermediate expression: {}",
"{}new intermediate expression: {:?}",
NESTED_INDENT.repeat(debug_indent_level),
self.format_counter(&intermediate_expression)
intermediate_expression
);
let intermediate_expression_operand = intermediate_expression.as_operand();
self.coverage_counters.intermediate_expressions.push(intermediate_expression);
Expand All @@ -497,13 +455,12 @@ impl<'a> MakeBcbCounters<'a> {
first_edge_counter_operand,
Op::Add,
some_sumup_edge_counter_operand.unwrap(),
|| Some(format!("{bcb:?}")),
);
debug!(
"{}{:?} gets a new counter (sum of predecessor counters): {}",
"{}{:?} gets a new counter (sum of predecessor counters): {:?}",
NESTED_INDENT.repeat(debug_indent_level),
bcb,
self.format_counter(&counter_kind)
counter_kind
);
self.coverage_counters.set_bcb_counter(bcb, counter_kind)
}
Expand Down Expand Up @@ -534,24 +491,23 @@ impl<'a> MakeBcbCounters<'a> {
self.coverage_counters.bcb_edge_counters.get(&(from_bcb, to_bcb))
{
debug!(
"{}Edge {:?}->{:?} already has a counter: {}",
"{}Edge {:?}->{:?} already has a counter: {:?}",
NESTED_INDENT.repeat(debug_indent_level),
from_bcb,
to_bcb,
self.format_counter(counter_kind)
counter_kind
);
return Ok(counter_kind.as_operand());
}

// Make a new counter to count this edge.
let counter_kind =
self.coverage_counters.make_counter(|| Some(format!("{from_bcb:?}->{to_bcb:?}")));
let counter_kind = self.coverage_counters.make_counter();
debug!(
"{}Edge {:?}->{:?} gets a new counter: {}",
"{}Edge {:?}->{:?} gets a new counter: {:?}",
NESTED_INDENT.repeat(debug_indent_level),
from_bcb,
to_bcb,
self.format_counter(&counter_kind)
counter_kind
);
self.coverage_counters.set_bcb_edge_counter(from_bcb, to_bcb, counter_kind)
}
Expand Down Expand Up @@ -710,9 +666,4 @@ impl<'a> MakeBcbCounters<'a> {
fn bcb_dominates(&self, dom: BasicCoverageBlock, node: BasicCoverageBlock) -> bool {
self.basic_coverage_blocks.dominates(dom, node)
}

#[inline]
fn format_counter(&self, counter_kind: &BcbCounter) -> String {
self.coverage_counters.debug_counters.format_counter(counter_kind)
}
}
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