Prefer switching on false for boolean switches

This ends up not really mattering because we generate a plain conditional branch in LLVM either
way.

6 files changed, 21 insertions, 24 deletions

diff --git a/src/librustc/middle/const_val.rs b/src/librustc/middle/const_val.rs
index f885a6d9569..11919db479c 100644
--- a/src/librustc/middle/const_val.rs
+++ b/src/librustc/middle/const_val.rs
@@ -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),
diff --git a/src/librustc/mir/mod.rs b/src/librustc/mir/mod.rs
index 5657ec157e8..98693d469ed 100644
--- a/src/librustc/mir/mod.rs
+++ b/src/librustc/mir/mod.rs
@@ -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> {
diff --git a/src/librustc_borrowck/borrowck/mir/elaborate_drops.rs b/src/librustc_borrowck/borrowck/mir/elaborate_drops.rs
index 144b0c2203a..44b85c31d86 100644
--- a/src/librustc_borrowck/borrowck/mir/elaborate_drops.rs
+++ b/src/librustc_borrowck/borrowck/mir/elaborate_drops.rs
@@ -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],
                 })
             }
         }
diff --git a/src/librustc_mir/build/expr/into.rs b/src/librustc_mir/build/expr/into.rs
index 537daa4a15b..f61b4a66077 100644
--- a/src/librustc_mir/build/expr/into.rs
+++ b/src/librustc_mir/build/expr/into.rs
@@ -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
diff --git a/src/librustc_mir/build/matches/mod.rs b/src/librustc_mir/build/matches/mod.rs
index 885965da1f9..812900b6bec 100644
--- a/src/librustc_mir/build/matches/mod.rs
+++ b/src/librustc_mir/build/matches/mod.rs
@@ -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 {
diff --git a/src/librustc_mir/build/matches/test.rs b/src/librustc_mir/build/matches/test.rs
index d9c2e6bb090..f268eda4c15 100644
--- a/src/librustc_mir/build/matches/test.rs
+++ b/src/librustc_mir/build/matches/test.rs
@@ -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
     }