Auto merge of rust-lang#111344 - cjgillot:gvn-simplify, r=<try>

Perform opportunistic simplifications during value numbering

Based on rust-lang#109597

Opening mostly for discussion. In its current form, I think this pass does too much. I want to remove the const-propagation part to make it simpler.

Author: bors

compiler/rustc_const_eval/src/interpret/cast.rs

@@ -416,7 +416,7 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
         }
     }
 
-    fn unsize_into(
+    pub fn unsize_into(
         &mut self,
         src: &OpTy<'tcx, M::Provenance>,
         cast_ty: TyAndLayout<'tcx>,

compiler/rustc_mir_transform/src/gvn.rs

@@ -7,10 +7,10 @@ fn main() -> () {
 
     bb0: {
         StorageLive(_1);
-        nop;
+        StorageLive(_2);
         _2 = const {ALLOC9: &&[(Option<i32>, &[&str])]};
         _1 = (*_2);
-        nop;
+        StorageDead(_2);
         StorageDead(_1);
         _0 = const ();
         return;

tests/mir-opt/const_allocation.main.GVN.after.32bit.mir

@@ -7,10 +7,10 @@ fn main() -> () {
 
     bb0: {
         StorageLive(_1);
-        nop;
+        StorageLive(_2);
         _2 = const {ALLOC9: &&[(Option<i32>, &[&str])]};
         _1 = (*_2);
-        nop;
+        StorageDead(_2);
         StorageDead(_1);
         _0 = const ();
         return;

tests/mir-opt/const_allocation.main.GVN.after.64bit.mir

@@ -7,10 +7,10 @@ fn main() -> () {
 
     bb0: {
         StorageLive(_1);
-        nop;
+        StorageLive(_2);
         _2 = const {ALLOC9: &&[(Option<i32>, &[&u8])]};
         _1 = (*_2);
-        nop;
+        StorageDead(_2);
         StorageDead(_1);
         _0 = const ();
         return;

tests/mir-opt/const_allocation2.main.GVN.after.32bit.mir

@@ -7,10 +7,10 @@ fn main() -> () {
 
     bb0: {
         StorageLive(_1);
-        nop;
+        StorageLive(_2);
         _2 = const {ALLOC9: &&[(Option<i32>, &[&u8])]};
         _1 = (*_2);
-        nop;
+        StorageDead(_2);
         StorageDead(_1);
         _0 = const ();
         return;

tests/mir-opt/const_allocation2.main.GVN.after.64bit.mir

@@ -7,10 +7,10 @@ fn main() -> () {
 
     bb0: {
         StorageLive(_1);
-        nop;
+        StorageLive(_2);
         _2 = const {ALLOC4: &&Packed};
         _1 = (*_2);
-        nop;
+        StorageDead(_2);
         StorageDead(_1);
         _0 = const ();
         return;

tests/mir-opt/const_allocation3.main.GVN.after.32bit.mir

@@ -7,10 +7,10 @@ fn main() -> () {
 
     bb0: {
         StorageLive(_1);
-        nop;
+        StorageLive(_2);
         _2 = const {ALLOC2: &&Packed};
         _1 = (*_2);
-        nop;
+        StorageDead(_2);
         StorageDead(_1);
         _0 = const ();
         return;

tests/mir-opt/const_allocation3.main.GVN.after.64bit.mir

@@ -24,9 +24,8 @@
       bb0: {
           StorageLive(_2);
 -         _2 = (const 1_i32, const false);
--         StorageLive(_3);
 +         _2 = const (1_i32, false);
-+         nop;
+          StorageLive(_3);
           _3 = &raw mut (_2.1: bool);
 -         _2 = (const 1_i32, const false);
 +         _2 = const (1_i32, false);
@@ -42,9 +41,8 @@
           StorageDead(_6);
           _0 = _5;
 -         StorageDead(_5);
--         StorageDead(_3);
-+         nop;
 +         nop;
+          StorageDead(_3);
           StorageDead(_2);
           return;
       }

tests/mir-opt/const_prop/address_of_pair.fn0.GVN.diff

@@ -18,11 +18,12 @@
           _2 = [const 0_u32, const 1_u32, const 2_u32, const 3_u32];
           StorageLive(_3);
           _3 = const 2_usize;
-          _4 = Len(_2);
+-         _4 = Len(_2);
 -         _5 = Lt(_3, _4);
 -         assert(move _5, "index out of bounds: the length is {} but the index is {}", move _4, _3) -> [success: bb1, unwind unreachable];
-+         _5 = Lt(const 2_usize, _4);
-+         assert(move _5, "index out of bounds: the length is {} but the index is {}", move _4, const 2_usize) -> [success: bb1, unwind unreachable];
++         _4 = const 4_usize;
++         _5 = const true;
++         assert(const true, "index out of bounds: the length is {} but the index is {}", const 4_usize, const 2_usize) -> [success: bb1, unwind unreachable];
       }
 
       bb1: {