Auto merge of #147079 - cjgillot:gvn-dbg-const, r=<try>

Replace SingleUseConsts by GVN.

Author: rust-bors[bot]

compiler/rustc_middle/src/mir/consts.rs

@@ -495,6 +495,11 @@ impl<'tcx> Const<'tcx> {
     /// Return true if any evaluation of this constant always returns the same value,
     /// taking into account even pointer identity tests.
     pub fn is_deterministic(&self) -> bool {
+        if self.ty().is_primitive() {
+            // Primitive types hold no provenance, so their result is deterministic.
+            return true;
+        }
+
         // Some constants may generate fresh allocations for pointers they contain,
         // so using the same constant twice can yield two different results.
         // Notably, valtrees purposefully generate new allocations.

compiler/rustc_mir_transform/src/gvn.rs

@@ -191,7 +191,6 @@ declare_passes! {
         Final
     };
     mod simplify_comparison_integral : SimplifyComparisonIntegral;
-    mod single_use_consts : SingleUseConsts;
     mod sroa : ScalarReplacementOfAggregates;
     mod strip_debuginfo : StripDebugInfo;
     mod unreachable_enum_branching : UnreachableEnumBranching;
@@ -709,7 +708,6 @@ pub(crate) fn run_optimization_passes<'tcx>(tcx: TyCtxt<'tcx>, body: &mut Body<'
             &simplify::SimplifyLocals::AfterGVN,
             &match_branches::MatchBranchSimplification,
             &dataflow_const_prop::DataflowConstProp,
-            &single_use_consts::SingleUseConsts,
             &o1(simplify_branches::SimplifyConstCondition::AfterConstProp),
             &jump_threading::JumpThreading,
             &early_otherwise_branch::EarlyOtherwiseBranch,

compiler/rustc_mir_transform/src/lib.rs

@@ -1,12 +1,13 @@
-// Check specific cases of sorting candidates in match lowering.
+//! Check specific cases of sorting candidates in match lowering.
+//@ compile-flags: -Zmir-opt-level=0
 
 // EMIT_MIR sort_candidates.constant_eq.SimplifyCfg-initial.after.mir
 fn constant_eq(s: &str, b: bool) -> u32 {
     // Check that we only test "a" once
 
     // CHECK-LABEL: fn constant_eq(
     // CHECK-NOT: const "a"
-    // CHECK: {{_[0-9]+}} = const "a" as &[u8] (Transmute);
+    // CHECK: eq({{.*}}, const "a")
     // CHECK-NOT: const "a"
     match (s, b) {
         ("a", _) if true => 1,
@@ -23,11 +24,16 @@ fn disjoint_ranges(x: i32, b: bool) -> u32 {
     // other candidates.
 
     // CHECK-LABEL: fn disjoint_ranges(
-    // CHECK: debug b => _2;
-    // CHECK: bb0: {
-    // CHECK: switchInt(copy _2) -> [0: [[jump:bb.*]], otherwise: {{bb.*}}];
+    // CHECK: debug b => [[b:_.*]];
+    // CHECK: [[tmp:_.*]] = copy [[b]];
+    // CHECK-NEXT: switchInt(move [[tmp]]) -> [0: [[jump:bb.*]], otherwise: {{bb.*}}];
     // CHECK: [[jump]]: {
+    // CHECK-NEXT: StorageDead([[tmp]]);
+    // CHECK-NEXT: goto -> [[jump3:bb.*]];
+    // CHECK: [[jump3]]: {
     // CHECK-NEXT: _0 = const 3_u32;
+    // CHECK-NEXT: goto -> [[jumpret:bb.*]];
+    // CHECK: [[jumpret]]: {
     // CHECK-NEXT: return;
     match x {
         0..10 if b => 0,

compiler/rustc_mir_transform/src/single_use_consts.rs

@@ -1,5 +1,5 @@
-- // MIR for `main` before SingleUseConsts
-+ // MIR for `main` after SingleUseConsts
+- // MIR for `main` before GVN
++ // MIR for `main` after GVN
 
   fn main() -> () {
       let mut _0: ();
@@ -55,73 +55,78 @@
       }
 
       bb0: {
-          nop;
--         _1 = const 1_u8;
-          nop;
--         _2 = const 2_u8;
-          nop;
--         _3 = const 3_u8;
+-         StorageLive(_1);
 +         nop;
+          _1 = const 1_u8;
+-         StorageLive(_2);
 +         nop;
+          _2 = const 2_u8;
+-         StorageLive(_3);
 +         nop;
+          _3 = const 3_u8;
           StorageLive(_4);
           StorageLive(_5);
           StorageLive(_6);
--         _6 = const 1_u8;
-+         nop;
+-         _6 = copy _1;
++         _6 = const 1_u8;
           StorageLive(_7);
--         _7 = const 2_u8;
--         _5 = const 3_u8;
-+         nop;
-+         nop;
+-         _7 = copy _2;
+-         _5 = Add(move _6, move _7);
++         _7 = const 2_u8;
++         _5 = const 3_u8;
           StorageDead(_7);
           StorageDead(_6);
           StorageLive(_8);
--         _8 = const 3_u8;
--         _4 = const 6_u8;
-+         nop;
-+         nop;
+-         _8 = copy _3;
+-         _4 = Add(move _5, move _8);
++         _8 = const 3_u8;
++         _4 = const 6_u8;
           StorageDead(_8);
           StorageDead(_5);
           StorageLive(_9);
--         _9 = const "hello, world!";
-+         nop;
+          _9 = const "hello, world!";
           StorageLive(_10);
           _10 = (const true, const false, const 123_u32);
           StorageLive(_11);
--         _11 = const Option::<u16>::Some(99_u16);
-+         nop;
+-         _11 = Option::<u16>::Some(const 99_u16);
++         _11 = const Option::<u16>::Some(99_u16);
           StorageLive(_12);
--         _12 = const Point {{ x: 32_u32, y: 32_u32 }};
-+         nop;
+-         _12 = Point { x: const 32_u32, y: const 32_u32 };
++         _12 = const Point {{ x: 32_u32, y: 32_u32 }};
           StorageLive(_13);
-          nop;
--         _14 = const 32_u32;
+-         StorageLive(_14);
+-         _14 = copy (_12.0: u32);
 +         nop;
++         _14 = const 32_u32;
           StorageLive(_15);
--         _15 = const 32_u32;
--         _13 = const 64_u32;
-+         nop;
-+         nop;
+-         _15 = copy (_12.1: u32);
+-         _13 = Add(move _14, move _15);
++         _15 = const 32_u32;
++         _13 = const 64_u32;
           StorageDead(_15);
-          nop;
+-         StorageDead(_14);
++         nop;
           _0 = const ();
           StorageDead(_13);
           StorageDead(_12);
           StorageDead(_11);
           StorageDead(_10);
           StorageDead(_9);
           StorageDead(_4);
-          nop;
-          nop;
-          nop;
+-         StorageDead(_3);
+-         StorageDead(_2);
+-         StorageDead(_1);
++         nop;
++         nop;
++         nop;
           return;
       }
   }
 
-  ALLOC0 (size: 8, align: 4) { .. }
-  
-  ALLOC1 (size: 4, align: 2) { .. }
-  
-  ALLOC2 (size: 13, align: 1) { .. }
+- ALLOC0 (size: 13, align: 1) { .. }
++ ALLOC0 (size: 8, align: 4) { .. }
++ 
++ ALLOC1 (size: 4, align: 2) { .. }
++ 
++ ALLOC2 (size: 13, align: 1) { .. }