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Prefer switching on false for boolean switches

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This ends up not really mattering because we generate a plain conditional branch in LLVM either
way.
This commit is contained in:
Simonas Kazlauskas 2017-02-02 22:03:23 +02:00
parent 4be18488a7
commit 8e00d28ff4
6 changed files with 21 additions and 24 deletions
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3
src/librustc/middle/const_val.rs
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@ -11,7 +11,6 @@
use syntax::symbol::InternedString;
use syntax::ast;
use std::rc::Rc;
use std::borrow::Cow;
use hir::def_id::DefId;
use rustc_const_math::*;
use self::ConstVal::*;
@ -19,8 +18,6 @@ pub use rustc_const_math::ConstInt;
use std::collections::BTreeMap;
pub static BOOL_SWITCH_TRUE: Cow<'static, [ConstInt]> = Cow::Borrowed(&[ConstInt::Infer(1)]);
#[derive(Clone, Debug, Hash, RustcEncodable, RustcDecodable, Eq, PartialEq)]
pub enum ConstVal {
Float(ConstFloat),

2
src/librustc/mir/mod.rs
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@ -447,7 +447,7 @@ pub struct Terminator<'tcx> {
}
/// For use in SwitchInt, for switching on bools.
pub static BOOL_SWITCH_TRUE: Cow<'static, [ConstInt]> = Cow::Borrowed(&[ConstInt::Infer(1)]);
pub static BOOL_SWITCH_FALSE: Cow<'static, [ConstInt]> = Cow::Borrowed(&[ConstInt::Infer(0)]);
#[derive(Clone, RustcEncodable, RustcDecodable)]
pub enum TerminatorKind<'tcx> {

4
src/librustc_borrowck/borrowck/mir/elaborate_drops.rs
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@ -846,8 +846,8 @@ impl<'b, 'tcx> ElaborateDropsCtxt<'b, 'tcx> {
self.new_block(c, is_cleanup, TerminatorKind::SwitchInt {
discr: Operand::Consume(flag),
switch_ty: boolty,
values: BOOL_SWITCH_TRUE.clone(),
targets: vec![on_set, on_unset],
values: BOOL_SWITCH_FALSE.clone(),
targets: vec![on_unset, on_set],
})
}
}

18
src/librustc_mir/build/expr/into.rs
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@ -72,8 +72,8 @@ impl<'a, 'gcx, 'tcx> Builder<'a, 'gcx, 'tcx> {
this.cfg.terminate(block, source_info, TerminatorKind::SwitchInt {
discr: operand,
switch_ty: this.hir.bool_ty(),
values: BOOL_SWITCH_TRUE.clone(),
targets: vec![then_block, else_block],
values: BOOL_SWITCH_FALSE.clone(),
targets: vec![else_block, then_block],
});
unpack!(then_block = this.into(destination, then_block, then_expr));
@ -113,13 +113,13 @@ impl<'a, 'gcx, 'tcx> Builder<'a, 'gcx, 'tcx> {
let lhs = unpack!(block = this.as_operand(block, lhs));
let blocks = match op {
LogicalOp::And => vec![else_block, false_block],
LogicalOp::Or => vec![true_block, else_block],
LogicalOp::And => vec![false_block, else_block],
LogicalOp::Or => vec![else_block, true_block],
};
this.cfg.terminate(block, source_info, TerminatorKind::SwitchInt {
discr: lhs,
switch_ty: this.hir.bool_ty(),
values: BOOL_SWITCH_TRUE.clone(),
values: BOOL_SWITCH_FALSE.clone(),
targets: blocks,
});
@ -127,8 +127,8 @@ impl<'a, 'gcx, 'tcx> Builder<'a, 'gcx, 'tcx> {
this.cfg.terminate(else_block, source_info, TerminatorKind::SwitchInt {
discr: rhs,
switch_ty: this.hir.bool_ty(),
values: BOOL_SWITCH_TRUE.clone(),
targets: vec![true_block, false_block],
values: BOOL_SWITCH_FALSE.clone(),
targets: vec![false_block, true_block],
});
this.cfg.push_assign_constant(
@ -191,8 +191,8 @@ impl<'a, 'gcx, 'tcx> Builder<'a, 'gcx, 'tcx> {
TerminatorKind::SwitchInt {
discr: cond,
switch_ty: this.hir.bool_ty(),
values: BOOL_SWITCH_TRUE.clone(),
targets: vec![body_block, exit_block],
values: BOOL_SWITCH_FALSE.clone(),
targets: vec![exit_block, body_block],
});
// if the test is false, there's no `break` to assign `destination`, so

4
src/librustc_mir/build/matches/mod.rs
View File

@ -675,8 +675,8 @@ impl<'a, 'gcx, 'tcx> Builder<'a, 'gcx, 'tcx> {
self.cfg.terminate(block, source_info, TerminatorKind::SwitchInt {
discr: cond,
switch_ty: self.hir.bool_ty(),
values: BOOL_SWITCH_TRUE.clone(),
targets: vec![arm_block, otherwise],
values: BOOL_SWITCH_FALSE.clone(),
targets: vec![otherwise, arm_block],
});
Some(otherwise)
} else {

14
src/librustc_mir/build/matches/test.rs
View File

@ -236,7 +236,7 @@ impl<'a, 'gcx, 'tcx> Builder<'a, 'gcx, 'tcx> {
&ConstVal::Bool(false) => vec![false_bb, true_bb],
v => span_bug!(test.span, "expected boolean value but got {:?}", v)
};
(BOOL_SWITCH_TRUE.clone(), vec![true_bb, false_bb], ret)
(BOOL_SWITCH_FALSE.clone(), vec![false_bb, true_bb], ret)
} else {
// The switch may be inexhaustive so we
// add a catch all block
@ -326,8 +326,8 @@ impl<'a, 'gcx, 'tcx> Builder<'a, 'gcx, 'tcx> {
self.cfg.terminate(eq_block, source_info, TerminatorKind::SwitchInt {
discr: Operand::Consume(eq_result),
switch_ty: self.hir.bool_ty(),
values: BOOL_SWITCH_TRUE.clone(),
targets: vec![block, fail],
values: BOOL_SWITCH_FALSE.clone(),
targets: vec![fail, block],
});
vec![block, fail]
} else {
@ -375,8 +375,8 @@ impl<'a, 'gcx, 'tcx> Builder<'a, 'gcx, 'tcx> {
self.cfg.terminate(block, source_info, TerminatorKind::SwitchInt {
discr: Operand::Consume(result),
switch_ty: self.hir.bool_ty(),
values: BOOL_SWITCH_TRUE.clone(),
targets: vec![true_bb, false_bb],
values: BOOL_SWITCH_FALSE.clone(),
targets: vec![false_bb, true_bb],
});
vec![true_bb, false_bb]
}
@ -403,8 +403,8 @@ impl<'a, 'gcx, 'tcx> Builder<'a, 'gcx, 'tcx> {
self.cfg.terminate(block, source_info, TerminatorKind::SwitchInt {
discr: Operand::Consume(result),
switch_ty: self.hir.bool_ty(),
values: BOOL_SWITCH_TRUE.clone(),
targets: vec![target_block, fail_block]
values: BOOL_SWITCH_FALSE.clone(),
targets: vec![fail_block, target_block]
});
target_block
}