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Merged
merged 4 commits into from
Sep 19, 2021
Merged

Start block is not allowed to have basic block predecessors #88968

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5118dd5
Start block is not allowed to have basic block predecessors
tmiasko Sep 14, 2021
4d614e1
Do not collapse goto chains beginning with the start block
tmiasko Sep 15, 2021
3489ba3
Remove support for reentrant start blocks from codegen
tmiasko Sep 14, 2021
f1f1c8f
./x.py test --bless
tmiasko Sep 18, 2021
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24 changes: 5 additions & 19 deletions compiler/rustc_codegen_ssa/src/mir/mod.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -152,20 +152,11 @@ pub fn codegen_mir<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>>(
}

let cleanup_kinds = analyze::cleanup_kinds(&mir);
// Allocate a `Block` for every basic block, except
// the start block, if nothing loops back to it.
let reentrant_start_block = !mir.predecessors()[mir::START_BLOCK].is_empty();
let cached_llbbs: IndexVec<mir::BasicBlock, Option<Bx::BasicBlock>> =
mir.basic_blocks()
.indices()
.map(|bb| {
if bb == mir::START_BLOCK && !reentrant_start_block {
Some(start_llbb)
} else {
None
}
})
.collect();
let cached_llbbs: IndexVec<mir::BasicBlock, Option<Bx::BasicBlock>> = mir
.basic_blocks()
.indices()
.map(|bb| if bb == mir::START_BLOCK { Some(start_llbb) } else { None })
.collect();

let mut fx = FunctionCx {
instance,
Expand Down Expand Up @@ -247,11 +238,6 @@ pub fn codegen_mir<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>>(
// Apply debuginfo to the newly allocated locals.
fx.debug_introduce_locals(&mut bx);

// Branch to the START block, if it's not the entry block.
if reentrant_start_block {
bx.br(fx.llbb(mir::START_BLOCK));
}

// Codegen the body of each block using reverse postorder
// FIXME(eddyb) reuse RPO iterator between `analysis` and this.
for (bb, _) in traversal::reverse_postorder(&mir) {
Expand Down
5 changes: 4 additions & 1 deletion compiler/rustc_const_eval/src/transform/validate.rs
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Expand Up @@ -9,7 +9,7 @@ use rustc_middle::mir::visit::{PlaceContext, Visitor};
use rustc_middle::mir::{
AggregateKind, BasicBlock, Body, BorrowKind, Local, Location, MirPhase, Operand, PlaceElem,
PlaceRef, ProjectionElem, Rvalue, SourceScope, Statement, StatementKind, Terminator,
TerminatorKind,
TerminatorKind, START_BLOCK,
};
use rustc_middle::ty::fold::BottomUpFolder;
use rustc_middle::ty::{self, ParamEnv, Ty, TyCtxt, TypeFoldable};
Expand Down Expand Up @@ -130,6 +130,9 @@ impl<'a, 'tcx> TypeChecker<'a, 'tcx> {
}

fn check_edge(&self, location: Location, bb: BasicBlock, edge_kind: EdgeKind) {
if bb == START_BLOCK {
self.fail(location, "start block must not have predecessors")
}
if let Some(bb) = self.body.basic_blocks().get(bb) {
let src = self.body.basic_blocks().get(location.block).unwrap();
match (src.is_cleanup, bb.is_cleanup, edge_kind) {
Expand Down
25 changes: 0 additions & 25 deletions compiler/rustc_mir_transform/src/simplify.rs
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Expand Up @@ -95,8 +95,6 @@ impl<'a, 'tcx> CfgSimplifier<'a, 'tcx> {
pub fn simplify(mut self) {
self.strip_nops();

let mut start = START_BLOCK;

// Vec of the blocks that should be merged. We store the indices here, instead of the
// statements itself to avoid moving the (relatively) large statements twice.
// We do not push the statements directly into the target block (`bb`) as that is slower
Expand All @@ -105,8 +103,6 @@ impl<'a, 'tcx> CfgSimplifier<'a, 'tcx> {
loop {
let mut changed = false;

self.collapse_goto_chain(&mut start, &mut changed);

for bb in self.basic_blocks.indices() {
if self.pred_count[bb] == 0 {
continue;
Expand Down Expand Up @@ -149,27 +145,6 @@ impl<'a, 'tcx> CfgSimplifier<'a, 'tcx> {
break;
}
}

if start != START_BLOCK {
debug_assert!(self.pred_count[START_BLOCK] == 0);
self.basic_blocks.swap(START_BLOCK, start);
self.pred_count.swap(START_BLOCK, start);

// pred_count == 1 if the start block has no predecessor _blocks_.
if self.pred_count[START_BLOCK] > 1 {
for (bb, data) in self.basic_blocks.iter_enumerated_mut() {
if self.pred_count[bb] == 0 {
continue;
}

for target in data.terminator_mut().successors_mut() {
if *target == start {
*target = START_BLOCK;
}
}
}
}
}
}

/// This function will return `None` if
Expand Down
14 changes: 8 additions & 6 deletions src/test/mir-opt/coverage_graphviz.main.InstrumentCoverage.0.dot
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Expand Up @@ -2,10 +2,12 @@ digraph Cov_0_3 {
graph [fontname="Courier, monospace"];
node [fontname="Courier, monospace"];
edge [fontname="Courier, monospace"];
bcb2__Cov_0_3 [shape="none", label=<<table border="0" cellborder="1" cellspacing="0"><tr><td bgcolor="gray" align="center" colspan="1">bcb2</td></tr><tr><td align="left" balign="left">Expression(bcb0 - bcb1) at 13:10-13:10<br/> 13:10-13:10: @4[0]: Coverage::Expression(4294967295) = 1 - 2 for $DIR/coverage_graphviz.rs:13:10 - 13:11</td></tr><tr><td align="left" balign="left">bb4: Goto</td></tr></table>>];
bcb1__Cov_0_3 [shape="none", label=<<table border="0" cellborder="1" cellspacing="0"><tr><td bgcolor="gray" align="center" colspan="1">bcb1</td></tr><tr><td align="left" balign="left">Counter(bcb1) at 12:13-12:18<br/> 12:13-12:18: @3[0]: Coverage::Expression(4294967294) = 2 + 0 for $DIR/coverage_graphviz.rs:15:1 - 15:2<br/>Expression(bcb1 + 0) at 15:2-15:2<br/> 15:2-15:2: @3.Return: return</td></tr><tr><td align="left" balign="left">bb3: Return</td></tr></table>>];
bcb0__Cov_0_3 [shape="none", label=<<table border="0" cellborder="1" cellspacing="0"><tr><td bgcolor="gray" align="center" colspan="1">bcb0</td></tr><tr><td align="left" balign="left"></td></tr><tr><td align="left" balign="left">Counter(bcb0) at 9:1-11:17<br/> 11:12-11:17: @1.Call: _2 = bar() -&gt; [return: bb2, unwind: bb5]</td></tr><tr><td align="left" balign="left">bb0: FalseUnwind<br/>bb1: Call</td></tr><tr><td align="left" balign="left">bb2: SwitchInt</td></tr></table>>];
bcb2__Cov_0_3 -> bcb0__Cov_0_3 [label=<>];
bcb0__Cov_0_3 -> bcb2__Cov_0_3 [label=<false>];
bcb0__Cov_0_3 -> bcb1__Cov_0_3 [label=<otherwise>];
bcb3__Cov_0_3 [shape="none", label=<<table border="0" cellborder="1" cellspacing="0"><tr><td bgcolor="gray" align="center" colspan="1">bcb3</td></tr><tr><td align="left" balign="left">Counter(bcb3) at 13:10-13:10<br/> 13:10-13:10: @5[0]: Coverage::Counter(2) for $DIR/coverage_graphviz.rs:13:10 - 13:11</td></tr><tr><td align="left" balign="left">bb5: Goto</td></tr></table>>];
bcb2__Cov_0_3 [shape="none", label=<<table border="0" cellborder="1" cellspacing="0"><tr><td bgcolor="gray" align="center" colspan="1">bcb2</td></tr><tr><td align="left" balign="left">Expression(bcb1:(bcb0 + bcb3) - bcb3) at 12:13-12:18<br/> 12:13-12:18: @4[0]: Coverage::Expression(4294967293) = 4294967294 + 0 for $DIR/coverage_graphviz.rs:15:1 - 15:2<br/>Expression(bcb2:(bcb1:(bcb0 + bcb3) - bcb3) + 0) at 15:2-15:2<br/> 15:2-15:2: @4.Return: return</td></tr><tr><td align="left" balign="left">bb4: Return</td></tr></table>>];
bcb1__Cov_0_3 [shape="none", label=<<table border="0" cellborder="1" cellspacing="0"><tr><td bgcolor="gray" align="center" colspan="1">bcb1</td></tr><tr><td align="left" balign="left">Expression(bcb0 + bcb3) at 10:5-11:17<br/> 11:12-11:17: @2.Call: _2 = bar() -&gt; [return: bb3, unwind: bb6]</td></tr><tr><td align="left" balign="left">bb1: FalseUnwind<br/>bb2: Call</td></tr><tr><td align="left" balign="left">bb3: SwitchInt</td></tr></table>>];
bcb0__Cov_0_3 [shape="none", label=<<table border="0" cellborder="1" cellspacing="0"><tr><td bgcolor="gray" align="center" colspan="1">bcb0</td></tr><tr><td align="left" balign="left"></td></tr><tr><td align="left" balign="left">Counter(bcb0) at 9:1-9:11<br/> </td></tr><tr><td align="left" balign="left">bb0: Goto</td></tr></table>>];
bcb3__Cov_0_3 -> bcb1__Cov_0_3 [label=<>];
bcb1__Cov_0_3 -> bcb3__Cov_0_3 [label=<false>];
bcb1__Cov_0_3 -> bcb2__Cov_0_3 [label=<otherwise>];
bcb0__Cov_0_3 -> bcb1__Cov_0_3 [label=<>];
}
2 changes: 1 addition & 1 deletion src/test/mir-opt/inline/inline_diverging.h.Inline.diff
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Expand Up @@ -47,7 +47,7 @@
+ _4 = &_2; // scope 1 at $DIR/inline-diverging.rs:22:5: 22:22
+ StorageLive(_9); // scope 1 at $DIR/inline-diverging.rs:22:5: 22:22
+ _9 = const (); // scope 1 at $DIR/inline-diverging.rs:22:5: 22:22
+ goto -> bb1; // scope 4 at $DIR/inline-diverging.rs:22:5: 22:22
+ goto -> bb1; // scope 5 at $DIR/inline-diverging.rs:22:5: 22:22
}

bb1: {
Expand Down
29 changes: 17 additions & 12 deletions src/test/mir-opt/instrument_coverage.main.InstrumentCoverage.diff
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Expand Up @@ -8,38 +8,43 @@
let mut _3: !; // in scope 0 at /the/src/instrument_coverage.rs:12:18: 14:10

bb0: {
+ Coverage::Counter(1) for /the/src/instrument_coverage.rs:10:1 - 12:17; // scope 0 at /the/src/instrument_coverage.rs:11:5: 15:6
falseUnwind -> [real: bb1, cleanup: bb5]; // scope 0 at /the/src/instrument_coverage.rs:11:5: 15:6
+ Coverage::Counter(1) for /the/src/instrument_coverage.rs:10:1 - 10:11; // scope 0 at /the/src/instrument_coverage.rs:11:5: 15:6
goto -> bb1; // scope 0 at /the/src/instrument_coverage.rs:11:5: 15:6
}

bb1: {
+ Coverage::Expression(4294967295) = 1 + 2 for /the/src/instrument_coverage.rs:11:5 - 12:17; // scope 0 at /the/src/instrument_coverage.rs:11:5: 15:6
falseUnwind -> [real: bb2, cleanup: bb6]; // scope 0 at /the/src/instrument_coverage.rs:11:5: 15:6
}

bb2: {
StorageLive(_2); // scope 0 at /the/src/instrument_coverage.rs:12:12: 12:17
_2 = bar() -> [return: bb2, unwind: bb5]; // scope 0 at /the/src/instrument_coverage.rs:12:12: 12:17
_2 = bar() -> [return: bb3, unwind: bb6]; // scope 0 at /the/src/instrument_coverage.rs:12:12: 12:17
// mir::Constant
// + span: /the/src/instrument_coverage.rs:12:12: 12:15
// + literal: Const { ty: fn() -> bool {bar}, val: Value(Scalar(<ZST>)) }
}

bb2: {
switchInt(move _2) -> [false: bb4, otherwise: bb3]; // scope 0 at /the/src/instrument_coverage.rs:12:12: 12:17
bb3: {
switchInt(move _2) -> [false: bb5, otherwise: bb4]; // scope 0 at /the/src/instrument_coverage.rs:12:12: 12:17
}

bb3: {
+ Coverage::Expression(4294967294) = 2 + 0 for /the/src/instrument_coverage.rs:16:1 - 16:2; // scope 0 at /the/src/instrument_coverage.rs:16:2: 16:2
+ Coverage::Counter(2) for /the/src/instrument_coverage.rs:13:13 - 13:18; // scope 0 at /the/src/instrument_coverage.rs:16:2: 16:2
bb4: {
+ Coverage::Expression(4294967293) = 4294967294 + 0 for /the/src/instrument_coverage.rs:16:1 - 16:2; // scope 0 at /the/src/instrument_coverage.rs:16:2: 16:2
+ Coverage::Expression(4294967294) = 4294967295 - 2 for /the/src/instrument_coverage.rs:13:13 - 13:18; // scope 0 at /the/src/instrument_coverage.rs:16:2: 16:2
_0 = const (); // scope 0 at /the/src/instrument_coverage.rs:13:13: 13:18
StorageDead(_2); // scope 0 at /the/src/instrument_coverage.rs:14:9: 14:10
return; // scope 0 at /the/src/instrument_coverage.rs:16:2: 16:2
}

bb4: {
+ Coverage::Expression(4294967295) = 1 - 2 for /the/src/instrument_coverage.rs:14:10 - 14:11; // scope 0 at /the/src/instrument_coverage.rs:11:5: 15:6
bb5: {
+ Coverage::Counter(2) for /the/src/instrument_coverage.rs:14:10 - 14:11; // scope 0 at /the/src/instrument_coverage.rs:11:5: 15:6
_1 = const (); // scope 0 at /the/src/instrument_coverage.rs:14:10: 14:10
StorageDead(_2); // scope 0 at /the/src/instrument_coverage.rs:14:9: 14:10
goto -> bb0; // scope 0 at /the/src/instrument_coverage.rs:11:5: 15:6
goto -> bb1; // scope 0 at /the/src/instrument_coverage.rs:11:5: 15:6
}

bb5 (cleanup): {
bb6 (cleanup): {
resume; // scope 0 at /the/src/instrument_coverage.rs:10:1: 16:2
}
}
Expand Down
34 changes: 19 additions & 15 deletions src/test/mir-opt/simplify_cfg.main.SimplifyCfg-early-opt.diff
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Expand Up @@ -8,40 +8,44 @@
let mut _3: !; // in scope 0 at $DIR/simplify_cfg.rs:9:18: 11:10

bb0: {
- goto -> bb1; // scope 0 at $DIR/simplify_cfg.rs:8:5: 12:6
goto -> bb1; // scope 0 at $DIR/simplify_cfg.rs:8:5: 12:6
}

bb1: {
- goto -> bb2; // scope 0 at $DIR/simplify_cfg.rs:8:5: 12:6
- }
-
- bb1: {
- bb2: {
StorageLive(_2); // scope 0 at $DIR/simplify_cfg.rs:9:12: 9:17
- _2 = bar() -> [return: bb2, unwind: bb5]; // scope 0 at $DIR/simplify_cfg.rs:9:12: 9:17
+ _2 = bar() -> [return: bb1, unwind: bb4]; // scope 0 at $DIR/simplify_cfg.rs:9:12: 9:17
- _2 = bar() -> [return: bb3, unwind: bb6]; // scope 0 at $DIR/simplify_cfg.rs:9:12: 9:17
+ _2 = bar() -> [return: bb2, unwind: bb5]; // scope 0 at $DIR/simplify_cfg.rs:9:12: 9:17
// mir::Constant
// + span: $DIR/simplify_cfg.rs:9:12: 9:15
// + literal: Const { ty: fn() -> bool {bar}, val: Value(Scalar(<ZST>)) }
}

- bb2: {
- switchInt(move _2) -> [false: bb4, otherwise: bb3]; // scope 0 at $DIR/simplify_cfg.rs:9:12: 9:17
+ bb1: {
+ switchInt(move _2) -> [false: bb3, otherwise: bb2]; // scope 0 at $DIR/simplify_cfg.rs:9:12: 9:17
}

- bb3: {
- switchInt(move _2) -> [false: bb5, otherwise: bb4]; // scope 0 at $DIR/simplify_cfg.rs:9:12: 9:17
+ bb2: {
+ switchInt(move _2) -> [false: bb4, otherwise: bb3]; // scope 0 at $DIR/simplify_cfg.rs:9:12: 9:17
}

- bb4: {
+ bb3: {
_0 = const (); // scope 0 at $DIR/simplify_cfg.rs:10:13: 10:18
StorageDead(_2); // scope 0 at $DIR/simplify_cfg.rs:11:9: 11:10
return; // scope 0 at $DIR/simplify_cfg.rs:13:2: 13:2
}

- bb4: {
+ bb3: {
- bb5: {
+ bb4: {
_1 = const (); // scope 0 at $DIR/simplify_cfg.rs:11:10: 11:10
StorageDead(_2); // scope 0 at $DIR/simplify_cfg.rs:11:9: 11:10
goto -> bb0; // scope 0 at $DIR/simplify_cfg.rs:8:5: 12:6
goto -> bb1; // scope 0 at $DIR/simplify_cfg.rs:8:5: 12:6
}

- bb5 (cleanup): {
+ bb4 (cleanup): {
- bb6 (cleanup): {
+ bb5 (cleanup): {
resume; // scope 0 at $DIR/simplify_cfg.rs:7:1: 13:2
}
}
Expand Down
29 changes: 12 additions & 17 deletions src/test/mir-opt/simplify_cfg.main.SimplifyCfg-initial.diff
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Original file line number Diff line number Diff line change
Expand Up @@ -8,38 +8,35 @@
let mut _3: !; // in scope 0 at $DIR/simplify_cfg.rs:9:18: 11:10

bb0: {
- goto -> bb1; // scope 0 at $DIR/simplify_cfg.rs:8:5: 12:6
+ falseUnwind -> [real: bb1, cleanup: bb5]; // scope 0 at $DIR/simplify_cfg.rs:8:5: 12:6
goto -> bb1; // scope 0 at $DIR/simplify_cfg.rs:8:5: 12:6
}

bb1: {
- falseUnwind -> [real: bb2, cleanup: bb11]; // scope 0 at $DIR/simplify_cfg.rs:8:5: 12:6
- }
-
- bb2: {
+ falseUnwind -> [real: bb2, cleanup: bb6]; // scope 0 at $DIR/simplify_cfg.rs:8:5: 12:6
}

bb2: {
StorageLive(_2); // scope 0 at $DIR/simplify_cfg.rs:9:12: 9:17
- _2 = bar() -> [return: bb3, unwind: bb11]; // scope 0 at $DIR/simplify_cfg.rs:9:12: 9:17
+ _2 = bar() -> [return: bb2, unwind: bb5]; // scope 0 at $DIR/simplify_cfg.rs:9:12: 9:17
+ _2 = bar() -> [return: bb3, unwind: bb6]; // scope 0 at $DIR/simplify_cfg.rs:9:12: 9:17
// mir::Constant
// + span: $DIR/simplify_cfg.rs:9:12: 9:15
// + literal: Const { ty: fn() -> bool {bar}, val: Value(Scalar(<ZST>)) }
}

- bb3: {
- switchInt(move _2) -> [false: bb5, otherwise: bb4]; // scope 0 at $DIR/simplify_cfg.rs:9:12: 9:17
+ bb2: {
+ switchInt(move _2) -> [false: bb4, otherwise: bb3]; // scope 0 at $DIR/simplify_cfg.rs:9:12: 9:17
bb3: {
switchInt(move _2) -> [false: bb5, otherwise: bb4]; // scope 0 at $DIR/simplify_cfg.rs:9:12: 9:17
}

- bb4: {
+ bb3: {
bb4: {
_0 = const (); // scope 0 at $DIR/simplify_cfg.rs:10:13: 10:18
- goto -> bb10; // scope 0 at $DIR/simplify_cfg.rs:10:13: 10:18
+ StorageDead(_2); // scope 0 at $DIR/simplify_cfg.rs:11:9: 11:10
+ return; // scope 0 at $DIR/simplify_cfg.rs:13:2: 13:2
}

- bb5: {
bb5: {
- goto -> bb8; // scope 0 at $DIR/simplify_cfg.rs:9:12: 9:17
- }
-
Expand All @@ -52,15 +49,13 @@
- }
-
- bb8: {
+ bb4: {
_1 = const (); // scope 0 at $DIR/simplify_cfg.rs:11:10: 11:10
- goto -> bb9; // scope 0 at $DIR/simplify_cfg.rs:9:9: 11:10
- }
-
- bb9: {
StorageDead(_2); // scope 0 at $DIR/simplify_cfg.rs:11:9: 11:10
- goto -> bb1; // scope 0 at $DIR/simplify_cfg.rs:8:5: 12:6
+ goto -> bb0; // scope 0 at $DIR/simplify_cfg.rs:8:5: 12:6
goto -> bb1; // scope 0 at $DIR/simplify_cfg.rs:8:5: 12:6
}

- bb10: {
Expand All @@ -69,7 +64,7 @@
- }
-
- bb11 (cleanup): {
+ bb5 (cleanup): {
+ bb6 (cleanup): {
resume; // scope 0 at $DIR/simplify_cfg.rs:7:1: 13:2
}
}
Expand Down
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