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Perform constant propagation into terminators #60745

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Merged
merged 4 commits into from
May 20, 2019
Merged

Perform constant propagation into terminators #60745

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8e99c76
[const-prop] Support propagating into Assert's `cond` Operand
wesleywiser May 11, 2019
3f5c743
[const-prop] Support propagating into SwitchInt's `discr` Operand
wesleywiser May 11, 2019
2baab0e
[const-prop] Remove catch all match and add FIXME
wesleywiser May 11, 2019
ec853ba
[const-prop] Don't const-prop into terminators unless mir-opt-level >= 2
wesleywiser May 11, 2019
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[const-prop] Support propagating into SwitchInt's discr Operand
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@wesleywiser
wesleywiser committed May 19, 2019
commit 3f5c743b531e948788db18ce8d514de06113cb35
7 changes: 7 additions & 0 deletions src/librustc_mir/transform/const_prop.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -736,6 +736,13 @@ impl<'b, 'a, 'tcx> MutVisitor<'tcx> for ConstPropagator<'b, 'a, 'tcx> {
}
}
},
TerminatorKind::SwitchInt { ref mut discr, switch_ty, .. } => {
if let Some(value) = self.eval_operand(&discr, source_info) {
if let ScalarMaybeUndef::Scalar(scalar) = self.ecx.read_scalar(value).unwrap() {
*discr = self.operand_from_scalar(scalar, switch_ty, source_info.span);
}
}
},
_ => {}
}
}
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38 changes: 38 additions & 0 deletions src/test/mir-opt/const_prop/switch_int.rs
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@@ -0,0 +1,38 @@
#[inline(never)]
fn foo(_: i32) { }

fn main() {
match 1 {
1 => foo(0),
_ => foo(-1),
}
}

// END RUST SOURCE
// START rustc.main.ConstProp.before.mir
// bb0: {
// ...
// _1 = const 1i32;
// switchInt(_1) -> [1i32: bb1, otherwise: bb2];
// }
// END rustc.main.ConstProp.before.mir
// START rustc.main.ConstProp.after.mir
// bb0: {
// ...
// switchInt(const 1i32) -> [1i32: bb1, otherwise: bb2];
// }
// END rustc.main.ConstProp.after.mir
// START rustc.main.SimplifyBranches-after-const-prop.before.mir
// bb0: {
// ...
// _1 = const 1i32;
// switchInt(const 1i32) -> [1i32: bb1, otherwise: bb2];
// }
// END rustc.main.SimplifyBranches-after-const-prop.before.mir
// START rustc.main.SimplifyBranches-after-const-prop.after.mir
// bb0: {
// ...
// _1 = const 1i32;
// goto -> bb1;
// }
// END rustc.main.SimplifyBranches-after-const-prop.after.mir
8 changes: 4 additions & 4 deletions src/test/mir-opt/simplify_if.rs
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Expand Up @@ -5,15 +5,15 @@ fn main() {
}

// END RUST SOURCE
// START rustc.main.SimplifyBranches-after-copy-prop.before.mir
// START rustc.main.SimplifyBranches-after-const-prop.before.mir
// bb0: {
// ...
// switchInt(const false) -> [false: bb3, otherwise: bb1];
// }
// END rustc.main.SimplifyBranches-after-copy-prop.before.mir
// START rustc.main.SimplifyBranches-after-copy-prop.after.mir
// END rustc.main.SimplifyBranches-after-const-prop.before.mir
// START rustc.main.SimplifyBranches-after-const-prop.after.mir
// bb0: {
// ...
// goto -> bb3;
// }
// END rustc.main.SimplifyBranches-after-copy-prop.after.mir
// END rustc.main.SimplifyBranches-after-const-prop.after.mir