Auto merge of rust-lang#116012 - cjgillot:gvn-const, r=oli-obk

Implement constant propagation on top of MIR SSA analysis This implements the idea I proposed in rust-lang#110719 (comment) Based on rust-lang#109597 The value numbering "GVN" pass formulates each rvalue that appears in MIR with an abstract form (the `Value` enum), and assigns an integer `VnIndex` to each. This abstract form can be used to deduplicate values, reusing an earlier local that holds the same value instead of recomputing. This part is proposed in rust-lang#109597. From this abstract representation, we can perform more involved simplifications, for example in rust-lang#111344. With the abstract representation `Value`, we can also attempt to evaluate each to a constant using the interpreter. This builds a `VnIndex -> OpTy` map. From this map, we can opportunistically replace an operand or a rvalue with a constant if their value has an associated `OpTy`. The most relevant commit is [Evaluated computed values to constants.](rust-lang@2767c49)" r? `@oli-obk`
rust-lang-ci · Dec 22, 2023 · 529a8c2 · 529a8c2
2 parents ef1b78e + a3dd640
commit 529a8c2
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diff --git a/compiler/rustc_mir_transform/src/const_prop.rs b/compiler/rustc_mir_transform/src/const_prop.rs
diff --git a/compiler/rustc_mir_transform/src/gvn.rs b/compiler/rustc_mir_transform/src/gvn.rs
@@ -109,7 +109,7 @@ pub struct GVN;
 
 impl<'tcx> MirPass<'tcx> for GVN {
     fn is_enabled(&self, sess: &rustc_session::Session) -> bool {
-        sess.mir_opt_level() >= 4
+        sess.mir_opt_level() >= 2
     }
 
     #[instrument(level = "trace", skip(self, tcx, body))]

diff --git a/compiler/rustc_mir_transform/src/lib.rs b/compiler/rustc_mir_transform/src/lib.rs
@@ -587,7 +587,6 @@ fn run_optimization_passes<'tcx>(tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
             // destroy the SSA property. It should still happen before const-propagation, so the
             // latter pass will leverage the created opportunities.
             &separate_const_switch::SeparateConstSwitch,
-            &const_prop::ConstProp,
             &gvn::GVN,
             &simplify::SimplifyLocals::AfterGVN,
             &dataflow_const_prop::DataflowConstProp,

diff --git a/tests/codegen/inherit_overflow.rs b/tests/codegen/inherit_overflow.rs
@@ -1,4 +1,4 @@
-// compile-flags: -Zmir-enable-passes=+Inline,+ConstProp --crate-type lib
+// compile-flags: -Zmir-enable-passes=+Inline,+GVN --crate-type lib
 // revisions: ASSERT NOASSERT
 //[ASSERT] compile-flags: -Coverflow-checks=on
 //[NOASSERT] compile-flags: -Coverflow-checks=off

diff --git a/tests/coverage/async2.cov-map b/tests/coverage/async2.cov-map
@@ -7,19 +7,17 @@ Number of file 0 mappings: 1
 - Code(Counter(0)) at (prev + 13, 1) to (start + 0, 23)
 
 Function name: async2::async_func::{closure#0}
-Raw bytes (28): 0x[01, 01, 02, 01, 05, 05, 02, 04, 01, 0d, 17, 03, 09, 05, 03, 0a, 02, 06, 02, 02, 06, 00, 07, 07, 01, 01, 00, 02]
+Raw bytes (26): 0x[01, 01, 01, 05, 00, 04, 01, 0d, 17, 03, 09, 05, 03, 0a, 02, 06, 00, 02, 06, 00, 07, 03, 01, 01, 00, 02]
 Number of files: 1
 - file 0 => global file 1
-Number of expressions: 2
-- expression 0 operands: lhs = Counter(0), rhs = Counter(1)
-- expression 1 operands: lhs = Counter(1), rhs = Expression(0, Sub)
+Number of expressions: 1
+- expression 0 operands: lhs = Counter(1), rhs = Zero
 Number of file 0 mappings: 4
 - Code(Counter(0)) at (prev + 13, 23) to (start + 3, 9)
 - Code(Counter(1)) at (prev + 3, 10) to (start + 2, 6)
-- Code(Expression(0, Sub)) at (prev + 2, 6) to (start + 0, 7)
-    = (c0 - c1)
-- Code(Expression(1, Add)) at (prev + 1, 1) to (start + 0, 2)
-    = (c1 + (c0 - c1))
+- Code(Zero) at (prev + 2, 6) to (start + 0, 7)
+- Code(Expression(0, Add)) at (prev + 1, 1) to (start + 0, 2)
+    = (c1 + Zero)
 
 Function name: async2::async_func_just_println
 Raw bytes (9): 0x[01, 01, 00, 01, 01, 15, 01, 00, 24]

diff --git a/tests/coverage/partial_eq.cov-map b/tests/coverage/partial_eq.cov-map
@@ -25,18 +25,18 @@ Number of file 0 mappings: 2
 - Code(Zero) at (prev + 0, 32) to (start + 0, 33)
 
 Function name: <partial_eq::Version as core::cmp::PartialOrd>::partial_cmp
-Raw bytes (22): 0x[01, 01, 04, 07, 0b, 05, 09, 0f, 15, 0d, 11, 02, 01, 04, 27, 00, 28, 03, 00, 30, 00, 31]
+Raw bytes (22): 0x[01, 01, 04, 07, 0b, 00, 09, 0f, 15, 00, 11, 02, 01, 04, 27, 00, 28, 03, 00, 30, 00, 31]
 Number of files: 1
 - file 0 => global file 1
 Number of expressions: 4
 - expression 0 operands: lhs = Expression(1, Add), rhs = Expression(2, Add)
-- expression 1 operands: lhs = Counter(1), rhs = Counter(2)
+- expression 1 operands: lhs = Zero, rhs = Counter(2)
 - expression 2 operands: lhs = Expression(3, Add), rhs = Counter(5)
-- expression 3 operands: lhs = Counter(3), rhs = Counter(4)
+- expression 3 operands: lhs = Zero, rhs = Counter(4)
 Number of file 0 mappings: 2
 - Code(Counter(0)) at (prev + 4, 39) to (start + 0, 40)
 - Code(Expression(0, Add)) at (prev + 0, 48) to (start + 0, 49)
-    = ((c1 + c2) + ((c3 + c4) + c5))
+    = ((Zero + c2) + ((Zero + c4) + c5))
 
 Function name: <partial_eq::Version as core::fmt::Debug>::fmt
 Raw bytes (9): 0x[01, 01, 00, 01, 01, 04, 11, 00, 16]

diff --git a/tests/incremental/hashes/for_loops.rs b/tests/incremental/hashes/for_loops.rs
@@ -103,9 +103,9 @@ pub fn change_iterable() {
 }
 
 #[cfg(not(any(cfail1,cfail4)))]
-#[rustc_clean(cfg="cfail2", except="hir_owner_nodes, promoted_mir")]
+#[rustc_clean(cfg="cfail2", except="hir_owner_nodes, promoted_mir, optimized_mir")]
 #[rustc_clean(cfg="cfail3")]
-#[rustc_clean(cfg="cfail5", except="hir_owner_nodes, promoted_mir")]
+#[rustc_clean(cfg="cfail5", except="hir_owner_nodes, promoted_mir, optimized_mir")]
 #[rustc_clean(cfg="cfail6")]
 pub fn change_iterable() {
     let mut _x = 0;

diff --git a/tests/incremental/string_constant.rs b/tests/incremental/string_constant.rs
@@ -17,7 +17,7 @@ pub mod x {
     }
 
     #[cfg(cfail2)]
-    #[rustc_clean(except = "hir_owner_nodes,promoted_mir", cfg = "cfail2")]
+    #[rustc_clean(except = "hir_owner_nodes,promoted_mir,optimized_mir", cfg = "cfail2")]
     pub fn x() {
         println!("{}", "2");
     }

diff --git a/...allocation.main.ConstProp.after.32bit.mir → ...const_allocation.main.GVN.after.32bit.mir b/...allocation.main.ConstProp.after.32bit.mir → ...const_allocation.main.GVN.after.32bit.mir
@@ -1,4 +1,4 @@
-// MIR for `main` after ConstProp
+// MIR for `main` after GVN
 
 fn main() -> () {
     let mut _0: ();
@@ -7,10 +7,10 @@ fn main() -> () {
 
     bb0: {
         StorageLive(_1);
-        StorageLive(_2);
+        nop;
         _2 = const {ALLOC9: &&[(Option<i32>, &[&str])]};
         _1 = (*_2);
-        StorageDead(_2);
+        nop;
         StorageDead(_1);
         _0 = const ();
         return;

diff --git a/...allocation.main.ConstProp.after.64bit.mir → ...const_allocation.main.GVN.after.64bit.mir b/...allocation.main.ConstProp.after.64bit.mir → ...const_allocation.main.GVN.after.64bit.mir
@@ -1,4 +1,4 @@
-// MIR for `main` after ConstProp
+// MIR for `main` after GVN
 
 fn main() -> () {
     let mut _0: ();
@@ -7,10 +7,10 @@ fn main() -> () {
 
     bb0: {
         StorageLive(_1);
-        StorageLive(_2);
+        nop;
         _2 = const {ALLOC9: &&[(Option<i32>, &[&str])]};
         _1 = (*_2);
-        StorageDead(_2);
+        nop;
         StorageDead(_1);
         _0 = const ();
         return;

diff --git a/tests/mir-opt/const_allocation.rs b/tests/mir-opt/const_allocation.rs
@@ -1,11 +1,11 @@
 // skip-filecheck
-// unit-test: ConstProp
+// unit-test: GVN
 // ignore-endian-big
 // EMIT_MIR_FOR_EACH_BIT_WIDTH
 static FOO: &[(Option<i32>, &[&str])] =
     &[(None, &[]), (None, &["foo", "bar"]), (Some(42), &["meh", "mop", "möp"])];
 
-// EMIT_MIR const_allocation.main.ConstProp.after.mir
+// EMIT_MIR const_allocation.main.GVN.after.mir
 fn main() {
     FOO;
 }
diff --git a/...llocation2.main.ConstProp.after.32bit.mir → ...onst_allocation2.main.GVN.after.32bit.mir b/...llocation2.main.ConstProp.after.32bit.mir → ...onst_allocation2.main.GVN.after.32bit.mir
@@ -1,4 +1,4 @@
-// MIR for `main` after ConstProp
+// MIR for `main` after GVN
 
 fn main() -> () {
     let mut _0: ();
@@ -7,10 +7,10 @@ fn main() -> () {
 
     bb0: {
         StorageLive(_1);
-        StorageLive(_2);
+        nop;
         _2 = const {ALLOC9: &&[(Option<i32>, &[&u8])]};
         _1 = (*_2);
-        StorageDead(_2);
+        nop;
         StorageDead(_1);
         _0 = const ();
         return;

diff --git a/...llocation2.main.ConstProp.after.64bit.mir → ...onst_allocation2.main.GVN.after.64bit.mir b/...llocation2.main.ConstProp.after.64bit.mir → ...onst_allocation2.main.GVN.after.64bit.mir
@@ -1,4 +1,4 @@
-// MIR for `main` after ConstProp
+// MIR for `main` after GVN
 
 fn main() -> () {
     let mut _0: ();
@@ -7,10 +7,10 @@ fn main() -> () {
 
     bb0: {
         StorageLive(_1);
-        StorageLive(_2);
+        nop;
         _2 = const {ALLOC9: &&[(Option<i32>, &[&u8])]};
         _1 = (*_2);
-        StorageDead(_2);
+        nop;
         StorageDead(_1);
         _0 = const ();
         return;

diff --git a/tests/mir-opt/const_allocation2.rs b/tests/mir-opt/const_allocation2.rs
@@ -1,8 +1,8 @@
 // skip-filecheck
-// unit-test: ConstProp
+// unit-test: GVN
 // ignore-endian-big
 // EMIT_MIR_FOR_EACH_BIT_WIDTH
-// EMIT_MIR const_allocation2.main.ConstProp.after.mir
+// EMIT_MIR const_allocation2.main.GVN.after.mir
 fn main() {
     FOO;
 }

diff --git a/...llocation3.main.ConstProp.after.32bit.mir → ...onst_allocation3.main.GVN.after.32bit.mir b/...llocation3.main.ConstProp.after.32bit.mir → ...onst_allocation3.main.GVN.after.32bit.mir
@@ -1,4 +1,4 @@
-// MIR for `main` after ConstProp
+// MIR for `main` after GVN
 
 fn main() -> () {
     let mut _0: ();
@@ -7,10 +7,10 @@ fn main() -> () {
 
     bb0: {
         StorageLive(_1);
-        StorageLive(_2);
+        nop;
         _2 = const {ALLOC4: &&Packed};
         _1 = (*_2);
-        StorageDead(_2);
+        nop;
         StorageDead(_1);
         _0 = const ();
         return;

diff --git a/...llocation3.main.ConstProp.after.64bit.mir → ...onst_allocation3.main.GVN.after.64bit.mir b/...llocation3.main.ConstProp.after.64bit.mir → ...onst_allocation3.main.GVN.after.64bit.mir
@@ -1,4 +1,4 @@
-// MIR for `main` after ConstProp
+// MIR for `main` after GVN
 
 fn main() -> () {
     let mut _0: ();
@@ -7,10 +7,10 @@ fn main() -> () {
 
     bb0: {
         StorageLive(_1);
-        StorageLive(_2);
+        nop;
         _2 = const {ALLOC2: &&Packed};
         _1 = (*_2);
-        StorageDead(_2);
+        nop;
         StorageDead(_1);
         _0 = const ();
         return;

diff --git a/tests/mir-opt/const_allocation3.rs b/tests/mir-opt/const_allocation3.rs
@@ -1,8 +1,8 @@
 // skip-filecheck
-// unit-test: ConstProp
+// unit-test: GVN
 // ignore-endian-big
 // EMIT_MIR_FOR_EACH_BIT_WIDTH
-// EMIT_MIR const_allocation3.main.ConstProp.after.mir
+// EMIT_MIR const_allocation3.main.GVN.after.mir
 fn main() {
     FOO;
 }

diff --git a/tests/mir-opt/const_debuginfo.main.ConstDebugInfo.diff b/tests/mir-opt/const_debuginfo.main.ConstDebugInfo.diff
@@ -34,7 +34,8 @@
                               debug f => _10;
                               let _11: std::option::Option<u16>;
                               scope 7 {
-                                  debug o => _11;
+-                                 debug o => _11;
++                                 debug o => const Option::<u16>::Some(99_u16);
                                   let _12: Point;
                                   scope 8 {
 -                                     debug p => _12;
@@ -54,11 +55,11 @@
       }
 
       bb0: {
-          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);
@@ -79,27 +80,27 @@
           StorageLive(_10);
           _10 = (const true, const false, const 123_u32);
           StorageLive(_11);
-          _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 }};
           StorageLive(_13);
-          StorageLive(_14);
+          nop;
           _14 = const 32_u32;
           StorageLive(_15);
           _15 = const 32_u32;
           _13 = const 64_u32;
           StorageDead(_15);
-          StorageDead(_14);
+          nop;
           _0 = const ();
           StorageDead(_13);
           StorageDead(_12);
           StorageDead(_11);
           StorageDead(_10);
           StorageDead(_9);
           StorageDead(_4);
-          StorageDead(_3);
-          StorageDead(_2);
-          StorageDead(_1);
+          nop;
+          nop;
+          nop;
           return;
       }
   }
@@ -108,3 +109,7 @@
       20 00 00 00 20 00 00 00                         │  ... ...
   }
 
+  ALLOC1 (size: 4, align: 2) {
+      01 00 63 00                                     │ ..c.
+  }
+
diff --git a/tests/mir-opt/const_debuginfo.rs b/tests/mir-opt/const_debuginfo.rs
@@ -1,5 +1,5 @@
 // unit-test: ConstDebugInfo
-// compile-flags: -C overflow-checks=no -Zmir-enable-passes=+ConstProp
+// compile-flags: -C overflow-checks=no -Zmir-enable-passes=+GVN
 
 struct Point {
     x: u32,
@@ -15,7 +15,7 @@ fn main() {
     // CHECK: debug sum => const 6_u8;
     // CHECK: debug s => const "hello, world!";
     // CHECK: debug f => {{_.*}};
-    // CHECK: debug o => {{_.*}};
+    // CHECK: debug o => const Option::<u16>::Some(99_u16);
     // CHECK: debug p => const Point
     // CHECK: debug a => const 64_u32;
     let x = 1u8;

diff --git a/...t_prop/address_of_pair.fn0.ConstProp.diff → ...t/const_prop/address_of_pair.fn0.GVN.diff b/...t_prop/address_of_pair.fn0.ConstProp.diff → ...t/const_prop/address_of_pair.fn0.GVN.diff
@@ -1,5 +1,5 @@
-- // MIR for `fn0` before ConstProp
-+ // MIR for `fn0` after ConstProp
+- // MIR for `fn0` before GVN
++ // MIR for `fn0` after GVN
 
   fn fn0() -> bool {
       let mut _0: bool;
@@ -23,24 +23,34 @@
 
       bb0: {
           StorageLive(_2);
-          _2 = (const 1_i32, const false);
-          StorageLive(_3);
+-         _2 = (const 1_i32, const false);
+-         StorageLive(_3);
++         _2 = const (1_i32, false);
++         nop;
           _3 = &raw mut (_2.1: bool);
-          _2 = (const 1_i32, const false);
+-         _2 = (const 1_i32, const false);
++         _2 = const (1_i32, false);
           StorageLive(_4);
           (*_3) = const true;
           _4 = const ();
           StorageDead(_4);
-          StorageLive(_5);
+-         StorageLive(_5);
++         nop;
           StorageLive(_6);
           _6 = (_2.1: bool);
           _5 = Not(move _6);
           StorageDead(_6);
           _0 = _5;
-          StorageDead(_5);
-          StorageDead(_3);
+-         StorageDead(_5);
+-         StorageDead(_3);
++         nop;
++         nop;
           StorageDead(_2);
           return;
       }
++ }
++ 
++ ALLOC0 (size: 8, align: 4) {
++     01 00 00 00 00 __ __ __                         │ .....░░░
   }
 
diff --git a/tests/mir-opt/const_prop/address_of_pair.rs b/tests/mir-opt/const_prop/address_of_pair.rs
@@ -1,6 +1,6 @@
-// unit-test: ConstProp
+// unit-test: GVN
 
-// EMIT_MIR address_of_pair.fn0.ConstProp.diff
+// EMIT_MIR address_of_pair.fn0.GVN.diff
 pub fn fn0() -> bool {
     // CHECK-LABEL: fn fn0(
     // CHECK: debug pair => [[pair:_.*]];