From 9f6f8620e188d5026f1b23d7714b4e41e2d92e30 Mon Sep 17 00:00:00 2001 From: =?UTF-8?q?Tomasz=20Mi=C4=85sko?= Date: Mon, 19 Apr 2021 00:00:00 +0000 Subject: [PATCH] Improve liveness analysis for generators Liveness analysis for generators assumes that execution always continues normally after a yield point, not accounting for the fact that generator could be dropped before completion. If generators captures any variables by reference, those variables could be used within a generator, or when the generator completes, but also after each yield point in the case the generator is dropped. Account for the case when generator is dropped after yielding, but before running to the completion. This effectively considers all variables captured by reference to be used after a yield point. --- compiler/rustc_passes/src/liveness.rs | 14 +++- src/test/ui/liveness/liveness-upvars.rs | 36 ++++++++++ src/test/ui/liveness/liveness-upvars.stderr | 80 +++++++++++++++------ 3 files changed, 107 insertions(+), 23 deletions(-) diff --git a/compiler/rustc_passes/src/liveness.rs b/compiler/rustc_passes/src/liveness.rs index 36d1a6c104421..edc0ff62bd5ec 100644 --- a/compiler/rustc_passes/src/liveness.rs +++ b/compiler/rustc_passes/src/liveness.rs @@ -435,7 +435,10 @@ impl<'tcx> Visitor<'tcx> for IrMaps<'tcx> { } // live nodes required for interesting control flow: - hir::ExprKind::If(..) | hir::ExprKind::Match(..) | hir::ExprKind::Loop(..) => { + hir::ExprKind::If(..) + | hir::ExprKind::Match(..) + | hir::ExprKind::Loop(..) + | hir::ExprKind::Yield(..) => { self.add_live_node_for_node(expr.hir_id, ExprNode(expr.span, expr.hir_id)); intravisit::walk_expr(self, expr); } @@ -469,7 +472,6 @@ impl<'tcx> Visitor<'tcx> for IrMaps<'tcx> { | hir::ExprKind::InlineAsm(..) | hir::ExprKind::LlvmInlineAsm(..) | hir::ExprKind::Box(..) - | hir::ExprKind::Yield(..) | hir::ExprKind::Type(..) | hir::ExprKind::Err | hir::ExprKind::Path(hir::QPath::TypeRelative(..)) @@ -866,6 +868,13 @@ impl<'a, 'tcx> Liveness<'a, 'tcx> { // at the label ident hir::ExprKind::Loop(ref blk, ..) => self.propagate_through_loop(expr, &blk, succ), + hir::ExprKind::Yield(ref e, ..) => { + let yield_ln = self.live_node(expr.hir_id, expr.span); + self.init_from_succ(yield_ln, succ); + self.merge_from_succ(yield_ln, self.exit_ln); + self.propagate_through_expr(e, yield_ln) + } + hir::ExprKind::If(ref cond, ref then, ref else_opt) => { // // (cond) @@ -1025,7 +1034,6 @@ impl<'a, 'tcx> Liveness<'a, 'tcx> { | hir::ExprKind::Type(ref e, _) | hir::ExprKind::DropTemps(ref e) | hir::ExprKind::Unary(_, ref e) - | hir::ExprKind::Yield(ref e, _) | hir::ExprKind::Repeat(ref e, _) => self.propagate_through_expr(&e, succ), hir::ExprKind::InlineAsm(ref asm) => { diff --git a/src/test/ui/liveness/liveness-upvars.rs b/src/test/ui/liveness/liveness-upvars.rs index 98ea4d71ccf4f..d446d57d39647 100644 --- a/src/test/ui/liveness/liveness-upvars.rs +++ b/src/test/ui/liveness/liveness-upvars.rs @@ -1,5 +1,6 @@ // edition:2018 // check-pass +#![feature(generators)] #![warn(unused)] #![allow(unreachable_code)] @@ -105,4 +106,39 @@ pub fn h() { }; } +async fn yield_now() { + todo!(); +} + +pub fn async_generator() { + let mut state: u32 = 0; + + let _ = async { + state = 1; + yield_now().await; + state = 2; + yield_now().await; + state = 3; + }; + + let _ = async move { + state = 4; //~ WARN value assigned to `state` is never read + //~| WARN unused variable: `state` + yield_now().await; + state = 5; //~ WARN value assigned to `state` is never read + }; +} + +pub fn generator() { + let mut s: u32 = 0; + let _ = |_| { + s = 0; + yield (); + s = 1; //~ WARN value assigned to `s` is never read + yield (s = 2); + s = yield (); //~ WARN value assigned to `s` is never read + s = 3; + }; +} + fn main() {} diff --git a/src/test/ui/liveness/liveness-upvars.stderr b/src/test/ui/liveness/liveness-upvars.stderr index 14fed91786436..d172330251365 100644 --- a/src/test/ui/liveness/liveness-upvars.stderr +++ b/src/test/ui/liveness/liveness-upvars.stderr @@ -1,11 +1,11 @@ warning: value assigned to `last` is never read - --> $DIR/liveness-upvars.rs:9:9 + --> $DIR/liveness-upvars.rs:10:9 | LL | last = Some(s); | ^^^^ | note: the lint level is defined here - --> $DIR/liveness-upvars.rs:3:9 + --> $DIR/liveness-upvars.rs:4:9 | LL | #![warn(unused)] | ^^^^^^ @@ -13,13 +13,13 @@ LL | #![warn(unused)] = help: maybe it is overwritten before being read? warning: unused variable: `last` - --> $DIR/liveness-upvars.rs:9:9 + --> $DIR/liveness-upvars.rs:10:9 | LL | last = Some(s); | ^^^^ | note: the lint level is defined here - --> $DIR/liveness-upvars.rs:3:9 + --> $DIR/liveness-upvars.rs:4:9 | LL | #![warn(unused)] | ^^^^^^ @@ -27,7 +27,7 @@ LL | #![warn(unused)] = help: did you mean to capture by reference instead? warning: unused variable: `sum` - --> $DIR/liveness-upvars.rs:21:9 + --> $DIR/liveness-upvars.rs:22:9 | LL | sum += x; | ^^^ @@ -35,7 +35,7 @@ LL | sum += x; = help: did you mean to capture by reference instead? warning: value captured by `c` is never read - --> $DIR/liveness-upvars.rs:31:9 + --> $DIR/liveness-upvars.rs:32:9 | LL | c = 1; | ^ @@ -43,7 +43,7 @@ LL | c = 1; = help: did you mean to capture by reference instead? warning: value captured by `c` is never read - --> $DIR/liveness-upvars.rs:35:9 + --> $DIR/liveness-upvars.rs:36:9 | LL | c = 1; | ^ @@ -51,7 +51,7 @@ LL | c = 1; = help: did you mean to capture by reference instead? warning: unused variable: `c` - --> $DIR/liveness-upvars.rs:41:9 + --> $DIR/liveness-upvars.rs:42:9 | LL | c += 1; | ^ @@ -59,7 +59,7 @@ LL | c += 1; = help: did you mean to capture by reference instead? warning: value assigned to `c` is never read - --> $DIR/liveness-upvars.rs:44:9 + --> $DIR/liveness-upvars.rs:45:9 | LL | c += 1; | ^ @@ -67,7 +67,7 @@ LL | c += 1; = help: maybe it is overwritten before being read? warning: unused variable: `c` - --> $DIR/liveness-upvars.rs:44:9 + --> $DIR/liveness-upvars.rs:45:9 | LL | c += 1; | ^ @@ -75,7 +75,7 @@ LL | c += 1; = help: did you mean to capture by reference instead? warning: value assigned to `c` is never read - --> $DIR/liveness-upvars.rs:57:9 + --> $DIR/liveness-upvars.rs:58:9 | LL | c += 1; | ^ @@ -83,7 +83,7 @@ LL | c += 1; = help: maybe it is overwritten before being read? warning: value assigned to `c` is never read - --> $DIR/liveness-upvars.rs:63:9 + --> $DIR/liveness-upvars.rs:64:9 | LL | c += 1; | ^ @@ -91,7 +91,7 @@ LL | c += 1; = help: maybe it is overwritten before being read? warning: value assigned to `d` is never read - --> $DIR/liveness-upvars.rs:72:13 + --> $DIR/liveness-upvars.rs:73:13 | LL | d = Some("d1"); | ^ @@ -99,7 +99,7 @@ LL | d = Some("d1"); = help: maybe it is overwritten before being read? warning: value assigned to `e` is never read - --> $DIR/liveness-upvars.rs:76:13 + --> $DIR/liveness-upvars.rs:77:13 | LL | e = Some("e1"); | ^ @@ -107,7 +107,7 @@ LL | e = Some("e1"); = help: maybe it is overwritten before being read? warning: value assigned to `e` is never read - --> $DIR/liveness-upvars.rs:78:13 + --> $DIR/liveness-upvars.rs:79:13 | LL | e = Some("e2"); | ^ @@ -115,7 +115,7 @@ LL | e = Some("e2"); = help: maybe it is overwritten before being read? warning: unused variable: `e` - --> $DIR/liveness-upvars.rs:76:13 + --> $DIR/liveness-upvars.rs:77:13 | LL | e = Some("e1"); | ^ @@ -123,7 +123,7 @@ LL | e = Some("e1"); = help: did you mean to capture by reference instead? warning: value assigned to `v` is never read - --> $DIR/liveness-upvars.rs:86:13 + --> $DIR/liveness-upvars.rs:87:13 | LL | v = T::default(); | ^ @@ -131,7 +131,7 @@ LL | v = T::default(); = help: maybe it is overwritten before being read? warning: value assigned to `z` is never read - --> $DIR/liveness-upvars.rs:98:17 + --> $DIR/liveness-upvars.rs:99:17 | LL | z = T::default(); | ^ @@ -139,12 +139,52 @@ LL | z = T::default(); = help: maybe it is overwritten before being read? warning: unused variable: `z` - --> $DIR/liveness-upvars.rs:98:17 + --> $DIR/liveness-upvars.rs:99:17 | LL | z = T::default(); | ^ | = help: did you mean to capture by reference instead? -warning: 17 warnings emitted +warning: value assigned to `state` is never read + --> $DIR/liveness-upvars.rs:125:9 + | +LL | state = 4; + | ^^^^^ + | + = help: maybe it is overwritten before being read? + +warning: value assigned to `state` is never read + --> $DIR/liveness-upvars.rs:128:9 + | +LL | state = 5; + | ^^^^^ + | + = help: maybe it is overwritten before being read? + +warning: unused variable: `state` + --> $DIR/liveness-upvars.rs:125:9 + | +LL | state = 4; + | ^^^^^ + | + = help: did you mean to capture by reference instead? + +warning: value assigned to `s` is never read + --> $DIR/liveness-upvars.rs:137:9 + | +LL | s = 1; + | ^ + | + = help: maybe it is overwritten before being read? + +warning: value assigned to `s` is never read + --> $DIR/liveness-upvars.rs:139:9 + | +LL | s = yield (); + | ^ + | + = help: maybe it is overwritten before being read? + +warning: 22 warnings emitted