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always add an unreachable branch on matches to give more info to llvm #45821

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merged 4 commits into from
Nov 14, 2017
Merged

always add an unreachable branch on matches to give more info to llvm #45821

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829b703
always add an unreachable branch on matches to give more info to llvm…
djzin Nov 7, 2017
aed0c9c
use lazy cached unreachable block - assign it to the function's closi…
djzin Nov 13, 2017
c503fe1
add optimization codegen tests
djzin Nov 13, 2017
5b1cc1d
don't send block back to be marked unreachable twice
djzin Nov 14, 2017
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2 changes: 1 addition & 1 deletion src/librustc_mir/build/matches/test.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -205,7 +205,7 @@ impl<'a, 'gcx, 'tcx> Builder<'a, 'gcx, 'tcx> {
if let Some(otherwise_block) = otherwise_block {
targets.push(otherwise_block);
} else {
values.pop();
targets.push(self.unreachable_block());
}
debug!("num_enum_variants: {}, tested variants: {:?}, variants: {:?}",
num_enum_variants, values, variants);
Expand Down
21 changes: 20 additions & 1 deletion src/librustc_mir/build/mod.rs
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Expand Up @@ -306,6 +306,8 @@ struct Builder<'a, 'gcx: 'a+'tcx, 'tcx: 'a> {
cached_resume_block: Option<BasicBlock>,
/// cached block with the RETURN terminator
cached_return_block: Option<BasicBlock>,
/// cached block with the UNREACHABLE terminator
cached_unreachable_block: Option<BasicBlock>,
}

struct CFG<'tcx> {
Expand Down Expand Up @@ -399,6 +401,11 @@ fn construct_fn<'a, 'gcx, 'tcx, A>(hir: Cx<'a, 'gcx, 'tcx>,
TerminatorKind::Goto { target: return_block });
builder.cfg.terminate(return_block, source_info,
TerminatorKind::Return);
// Attribute any unreachable codepaths to the function's closing brace
if let Some(unreachable_block) = builder.cached_unreachable_block {
builder.cfg.terminate(unreachable_block, source_info,
TerminatorKind::Unreachable);
}
return_block.unit()
}));
assert_eq!(block, builder.return_block());
Expand Down Expand Up @@ -501,7 +508,8 @@ impl<'a, 'gcx, 'tcx> Builder<'a, 'gcx, 'tcx> {
var_indices: NodeMap(),
unit_temp: None,
cached_resume_block: None,
cached_return_block: None
cached_return_block: None,
cached_unreachable_block: None,
};

assert_eq!(builder.cfg.start_new_block(), START_BLOCK);
Expand Down Expand Up @@ -630,6 +638,17 @@ impl<'a, 'gcx, 'tcx> Builder<'a, 'gcx, 'tcx> {
}
}
}

fn unreachable_block(&mut self) -> BasicBlock {
match self.cached_unreachable_block {
Some(ub) => ub,
None => {
let ub = self.cfg.start_new_block();
self.cached_unreachable_block = Some(ub);
ub
}
}
}
}

///////////////////////////////////////////////////////////////////////////
Expand Down
44 changes: 44 additions & 0 deletions src/test/codegen/match-optimizes-away.rs
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@@ -0,0 +1,44 @@
// Copyright 2017 The Rust Project Developers. See the COPYRIGHT
// file at the top-level directory of this distribution and at
// http://rust-lang.org/COPYRIGHT.
//
// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
// option. This file may not be copied, modified, or distributed
// except according to those terms.
//
// no-system-llvm
// compile-flags: -O
#![crate_type="lib"]

pub enum Three { First, Second, Third }
use Three::*;

pub enum Four { First, Second, Third, Fourth }
use Four::*;
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It'd be nice if we made a lint against this, set to error at least for the Rust codebase...

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wow thanks for catching this, I had them in 2 separate files before & just assumed that any warning would trap here...

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There are warnings from the matches themselves but most tests are written without warning avoidance in mind so we'd have to do a lot of work to ban warnings from tests.

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Should probably as a matter of course put #![deny(warnings)] on these tests where it is appropriate (at least I will do that in future)


#[no_mangle]
pub fn three_valued(x: Three) -> Three {
// CHECK-LABEL: @three_valued
// CHECK-NEXT: {{^.*:$}}
// CHECK-NEXT: ret i8 %0
match x {
First => First,
Second => Second,
Third => Third,
}
}

#[no_mangle]
pub fn four_valued(x: Four) -> Four {
// CHECK-LABEL: @four_valued
// CHECK-NEXT: {{^.*:$}}
// CHECK-NEXT: ret i8 %0
match x {
First => First,
Second => Second,
Third => Third,
Fourth => Fourth,
}
}
9 changes: 6 additions & 3 deletions src/test/codegen/match.rs
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Expand Up @@ -21,12 +21,15 @@ pub enum E {
#[no_mangle]
pub fn exhaustive_match(e: E) {
// CHECK: switch{{.*}}, label %[[OTHERWISE:[a-zA-Z0-9_]+]] [
// CHECK-NEXT: i[[TY:[0-9]+]] [[DISCR:[0-9]+]], label %[[TRUE:[a-zA-Z0-9_]+]]
// CHECK-NEXT: i[[TY:[0-9]+]] [[DISCR:[0-9]+]], label %[[A:[a-zA-Z0-9_]+]]
// CHECK-NEXT: i[[TY:[0-9]+]] [[DISCR:[0-9]+]], label %[[B:[a-zA-Z0-9_]+]]
// CHECK-NEXT: ]
// CHECK: [[TRUE]]:
// CHECK: [[A]]:
// CHECK-NEXT: br label %[[EXIT:[a-zA-Z0-9_]+]]
// CHECK: [[OTHERWISE]]:
// CHECK: [[B]]:
// CHECK-NEXT: br label %[[EXIT:[a-zA-Z0-9_]+]]
// CHECK: [[OTHERWISE]]:
// CHECK-NEXT: unreachable
match e {
E::A => (),
E::B => (),
Expand Down
58 changes: 32 additions & 26 deletions src/test/mir-opt/match_false_edges.rs
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Expand Up @@ -54,53 +54,56 @@ fn main() {
// ...
// _2 = std::option::Option<i32>::Some(const 42i32,);
// _5 = discriminant(_2);
// switchInt(_5) -> [0isize: bb5, otherwise: bb3];
// switchInt(_5) -> [0isize: bb5, 1isize: bb3, otherwise: bb7];
// }
// bb1: { // arm1
// StorageLive(_7);
// _7 = _3;
// _1 = (const 1i32, _7);
// StorageDead(_7);
// goto -> bb11;
// goto -> bb12;
// }
// bb2: { // binding3(empty) and arm3
// _1 = (const 3i32, const 3i32);
// goto -> bb11;
// goto -> bb12;
// }
// bb3: {
// falseEdges -> [real: bb7, imaginary: bb4]; //pre_binding1
// falseEdges -> [real: bb8, imaginary: bb4]; //pre_binding1
// }
// bb4: {
// falseEdges -> [real: bb10, imaginary: bb5]; //pre_binding2
// falseEdges -> [real: bb11, imaginary: bb5]; //pre_binding2
// }
// bb5: {
// falseEdges -> [real: bb2, imaginary: bb6]; //pre_binding3
// }
// bb6: {
// unreachable;
// }
// bb7: { // binding1 and guard
// bb7: {
// unreachable;
// }
// bb8: { // binding1 and guard
// StorageLive(_3);
// _3 = ((_2 as Some).0: i32);
// StorageLive(_6);
// _6 = const guard() -> bb8;
// _6 = const guard() -> bb9;
// }
// bb8: { // end of guard
// switchInt(_6) -> [0u8: bb9, otherwise: bb1];
// bb9: { // end of guard
// switchInt(_6) -> [0u8: bb10, otherwise: bb1];
// }
// bb9: { // to pre_binding2
// bb10: { // to pre_binding2
// falseEdges -> [real: bb4, imaginary: bb4];
// }
// bb10: { // bindingNoLandingPads.before.mir2 and arm2
// bb11: { // bindingNoLandingPads.before.mir2 and arm2
// StorageLive(_4);
// _4 = ((_2 as Some).0: i32);
// StorageLive(_8);
// _8 = _4;
// _1 = (const 2i32, _8);
// StorageDead(_8);
// goto -> bb11;
// goto -> bb12;
// }
// bb11: {
// bb12: {
// ...
// return;
// }
Expand All @@ -111,53 +114,56 @@ fn main() {
// ...
// _2 = std::option::Option<i32>::Some(const 42i32,);
// _5 = discriminant(_2);
// switchInt(_5) -> [0isize: bb4, otherwise: bb3];
// switchInt(_5) -> [0isize: bb4, 1isize: bb3, otherwise: bb7];
// }
// bb1: { // arm1
// StorageLive(_7);
// _7 = _3;
// _1 = (const 1i32, _7);
// StorageDead(_7);
// goto -> bb11;
// goto -> bb12;
// }
// bb2: { // binding3(empty) and arm3
// _1 = (const 3i32, const 3i32);
// goto -> bb11;
// goto -> bb12;
// }
// bb3: {
// falseEdges -> [real: bb7, imaginary: bb4]; //pre_binding1
// falseEdges -> [real: bb8, imaginary: bb4]; //pre_binding1
// }
// bb4: {
// falseEdges -> [real: bb2, imaginary: bb5]; //pre_binding2
// }
// bb5: {
// falseEdges -> [real: bb10, imaginary: bb6]; //pre_binding3
// falseEdges -> [real: bb11, imaginary: bb6]; //pre_binding3
// }
// bb6: {
// unreachable;
// }
// bb7: { // binding1 and guard
// bb7: {
// unreachable;
// }
// bb8: { // binding1 and guard
// StorageLive(_3);
// _3 = ((_2 as Some).0: i32);
// StorageLive(_6);
// _6 = const guard() -> bb8;
// _6 = const guard() -> bb9;
// }
// bb8: { // end of guard
// switchInt(_6) -> [0u8: bb9, otherwise: bb1];
// bb9: { // end of guard
// switchInt(_6) -> [0u8: bb10, otherwise: bb1];
// }
// bb9: { // to pre_binding2
// bb10: { // to pre_binding2
// falseEdges -> [real: bb5, imaginary: bb4];
// }
// bb10: { // binding2 and arm2
// bb11: { // binding2 and arm2
// StorageLive(_4);
// _4 = ((_2 as Some).0: i32);
// StorageLive(_8);
// _8 = _4;
// _1 = (const 2i32, _8);
// StorageDead(_8);
// goto -> bb11;
// goto -> bb12;
// }
// bb11: {
// bb12: {
// ...
// return;
// }
Expand Down