Prune MIR based on types before codegen.

Author: cjgillot

compiler/rustc_codegen_ssa/src/mir/mod.rs

@@ -7,7 +7,10 @@ use rustc_middle::mir::{Body, Local, UnwindTerminateReason, traversal};
 use rustc_middle::ty::layout::{FnAbiOf, HasTyCtxt, HasTypingEnv, TyAndLayout};
 use rustc_middle::ty::{self, Instance, Ty, TyCtxt, TypeVisitableExt};
 use rustc_middle::{bug, mir, span_bug};
-use rustc_mir_transform::{add_call_guards, dump_mir, pass_manager};
+use rustc_mir_transform::{
+    add_call_guards, dump_mir, pass_manager, remove_noop_landing_pads, remove_unneeded_drops,
+    remove_zsts, simplify, simplify_branches, unreachable_enum_branching, unreachable_prop,
+};
 use rustc_target::callconv::{FnAbi, PassMode};
 use tracing::{debug, instrument};
 
@@ -172,6 +175,15 @@ pub fn codegen_mir<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>>(
         cx.tcx(),
         &mut mir,
         &[
+            // Monomorphization may introduce ZST, non-drop and uninhabited types.
+            &remove_zsts::RemoveZsts,
+            &remove_unneeded_drops::RemoveUnneededDrops,
+            &unreachable_enum_branching::UnreachableEnumBranching,
+            &unreachable_prop::UnreachablePropagation,
+            &remove_noop_landing_pads::RemoveNoopLandingPads,
+            &simplify_branches::SimplifyConstCondition::Monomorphic,
+            &simplify::SimplifyCfg::Monomorphic,
+            &simplify::SimplifyLocals::Monomorphic,
             // Some cleanup necessary at least for LLVM and potentially other codegen backends.
             &add_call_guards::CriticalCallEdges,
             // Dump the end result for testing and debugging purposes.

compiler/rustc_mir_transform/src/lib.rs

@@ -79,7 +79,7 @@ mod ssa;
 macro_rules! declare_passes {
     (
         $(
-            $vis:vis mod $mod_name:ident : $($pass_name:ident $( { $($ident:ident),* } )?),+ $(,)?;
+            $vis:vis mod $mod_name:ident : $($pass_name:ident $( { $($ident:ident),* $(,)? } )?),+ $(,)?;
         )*
     ) => {
         $(
@@ -159,12 +159,12 @@ declare_passes! {
     mod prettify : ReorderBasicBlocks, ReorderLocals;
     mod promote_consts : PromoteTemps;
     mod ref_prop : ReferencePropagation;
-    mod remove_noop_landing_pads : RemoveNoopLandingPads;
+    pub mod remove_noop_landing_pads : RemoveNoopLandingPads;
     mod remove_place_mention : RemovePlaceMention;
     mod remove_storage_markers : RemoveStorageMarkers;
     mod remove_uninit_drops : RemoveUninitDrops;
-    mod remove_unneeded_drops : RemoveUnneededDrops;
-    mod remove_zsts : RemoveZsts;
+    pub mod remove_unneeded_drops : RemoveUnneededDrops;
+    pub mod remove_zsts : RemoveZsts;
     mod required_consts : RequiredConstsVisitor;
     mod post_analysis_normalize : PostAnalysisNormalize;
     mod sanity_check : SanityCheck;
@@ -178,23 +178,26 @@ declare_passes! {
             PreOptimizations,
             Final,
             MakeShim,
-            AfterUnreachableEnumBranching
+            AfterUnreachableEnumBranching,
+            Monomorphic,
         },
         SimplifyLocals {
             BeforeConstProp,
             AfterGVN,
-            Final
+            Final,
+            Monomorphic,
         };
-    mod simplify_branches : SimplifyConstCondition {
+    pub mod simplify_branches : SimplifyConstCondition {
         AfterConstProp,
-        Final
+        Final,
+        Monomorphic,
     };
     mod simplify_comparison_integral : SimplifyComparisonIntegral;
     mod single_use_consts : SingleUseConsts;
     mod sroa : ScalarReplacementOfAggregates;
     mod strip_debuginfo : StripDebugInfo;
-    mod unreachable_enum_branching : UnreachableEnumBranching;
-    mod unreachable_prop : UnreachablePropagation;
+    pub mod unreachable_enum_branching : UnreachableEnumBranching;
+    pub mod unreachable_prop : UnreachablePropagation;
     mod validate : Validator;
 }
 

compiler/rustc_mir_transform/src/remove_noop_landing_pads.rs

@@ -9,7 +9,7 @@ use crate::patch::MirPatch;
 /// A pass that removes noop landing pads and replaces jumps to them with
 /// `UnwindAction::Continue`. This is important because otherwise LLVM generates
 /// terrible code for these.
-pub(super) struct RemoveNoopLandingPads;
+pub struct RemoveNoopLandingPads;
 
 impl<'tcx> crate::MirPass<'tcx> for RemoveNoopLandingPads {
     fn is_enabled(&self, sess: &rustc_session::Session) -> bool {

compiler/rustc_mir_transform/src/remove_unneeded_drops.rs

@@ -11,7 +11,7 @@ use tracing::{debug, trace};
 
 use super::simplify::simplify_cfg;
 
-pub(super) struct RemoveUnneededDrops;
+pub struct RemoveUnneededDrops;
 
 impl<'tcx> crate::MirPass<'tcx> for RemoveUnneededDrops {
     fn run_pass(&self, tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {

compiler/rustc_mir_transform/src/remove_zsts.rs

@@ -4,7 +4,7 @@ use rustc_middle::mir::visit::*;
 use rustc_middle::mir::*;
 use rustc_middle::ty::{self, Ty, TyCtxt};
 
-pub(super) struct RemoveZsts;
+pub struct RemoveZsts;
 
 impl<'tcx> crate::MirPass<'tcx> for RemoveZsts {
     fn is_enabled(&self, sess: &rustc_session::Session) -> bool {

compiler/rustc_mir_transform/src/simplify.rs

@@ -42,7 +42,7 @@ use rustc_span::DUMMY_SP;
 use smallvec::SmallVec;
 use tracing::{debug, trace};
 
-pub(super) enum SimplifyCfg {
+pub enum SimplifyCfg {
     Initial,
     PromoteConsts,
     RemoveFalseEdges,
@@ -54,6 +54,7 @@ pub(super) enum SimplifyCfg {
     Final,
     MakeShim,
     AfterUnreachableEnumBranching,
+    Monomorphic,
 }
 
 impl SimplifyCfg {
@@ -69,6 +70,7 @@ impl SimplifyCfg {
             SimplifyCfg::AfterUnreachableEnumBranching => {
                 "SimplifyCfg-after-unreachable-enum-branching"
             }
+            SimplifyCfg::Monomorphic => "SimplifyCfg-monomorphic",
         }
     }
 }
@@ -391,10 +393,11 @@ pub(super) fn remove_dead_blocks(body: &mut Body<'_>) {
     }
 }
 
-pub(super) enum SimplifyLocals {
+pub enum SimplifyLocals {
     BeforeConstProp,
     AfterGVN,
     Final,
+    Monomorphic,
 }
 
 impl<'tcx> crate::MirPass<'tcx> for SimplifyLocals {
@@ -403,6 +406,7 @@ impl<'tcx> crate::MirPass<'tcx> for SimplifyLocals {
             SimplifyLocals::BeforeConstProp => "SimplifyLocals-before-const-prop",
             SimplifyLocals::AfterGVN => "SimplifyLocals-after-value-numbering",
             SimplifyLocals::Final => "SimplifyLocals-final",
+            SimplifyLocals::Monomorphic => "SimplifyLocals-monomorphic",
         }
     }
 

compiler/rustc_mir_transform/src/simplify_branches.rs

@@ -2,9 +2,10 @@ use rustc_middle::mir::*;
 use rustc_middle::ty::TyCtxt;
 use tracing::trace;
 
-pub(super) enum SimplifyConstCondition {
+pub enum SimplifyConstCondition {
     AfterConstProp,
     Final,
+    Monomorphic,
 }
 
 /// A pass that replaces a branch with a goto when its condition is known.
@@ -13,6 +14,7 @@ impl<'tcx> crate::MirPass<'tcx> for SimplifyConstCondition {
         match self {
             SimplifyConstCondition::AfterConstProp => "SimplifyConstCondition-after-const-prop",
             SimplifyConstCondition::Final => "SimplifyConstCondition-final",
+            SimplifyConstCondition::Monomorphic => "SimplifyConstCondition-monomorphic",
         }
     }
 

compiler/rustc_mir_transform/src/unreachable_enum_branching.rs

@@ -13,7 +13,7 @@ use tracing::trace;
 
 use crate::patch::MirPatch;
 
-pub(super) struct UnreachableEnumBranching;
+pub struct UnreachableEnumBranching;
 
 fn get_discriminant_local(terminator: &TerminatorKind<'_>) -> Option<Local> {
     if let TerminatorKind::SwitchInt { discr: Operand::Move(p), .. } = terminator {

compiler/rustc_mir_transform/src/unreachable_prop.rs

@@ -11,7 +11,7 @@ use rustc_middle::ty::{self, TyCtxt};
 
 use crate::patch::MirPatch;
 
-pub(super) struct UnreachablePropagation;
+pub struct UnreachablePropagation;
 
 impl crate::MirPass<'_> for UnreachablePropagation {
     fn is_enabled(&self, sess: &rustc_session::Session) -> bool {

tests/codegen/intrinsics/transmute.rs

@@ -56,7 +56,7 @@ pub unsafe fn check_bigger_array(x: [u32; 3]) -> [u32; 7] {
 
 // CHECK-LABEL: @check_to_empty_array(
 #[no_mangle]
-#[custom_mir(dialect = "runtime", phase = "optimized")]
+#[custom_mir(dialect = "runtime", phase = "monomorphic")]
 pub unsafe fn check_to_empty_array(x: [u32; 5]) -> [u32; 0] {
     // CHECK-NOT: trap
     // CHECK: call void @llvm.trap
@@ -397,7 +397,7 @@ pub unsafe fn check_issue_109992(x: ()) -> [(); 1] {
 
 // CHECK-LABEL: @check_unit_to_never(
 #[no_mangle]
-#[custom_mir(dialect = "runtime", phase = "optimized")]
+#[custom_mir(dialect = "runtime", phase = "monomorphic")]
 pub unsafe fn check_unit_to_never(x: ()) {
     // This uses custom MIR to avoid MIR optimizations having removed ZST ops.