Auto merge of #144389 - scottmcm:no-more-mir-cast-assume, r=davidtwco

MIR-build: No longer emit assumes in enum-as casting

This just uses the `valid_range` from the backend, so it's duplicating the range metadata that now we include on parameters and loads, and thus no longer seems to be useful -- notably there's no codegen test failures from removing it.

(Because it's using data from the same source as the backend annotations, it doesn't do anything to mitigate things like rust-lang/rust#144388 where the range in the layout is more permissive than the actual possible discriminants.  A variant of this that actually checked the discriminants more specifically might be useful, so could potentially be added in future, but I don't think the *current* checks are actually providing value.)

r? mir

Randomly turns out that this
Fixes https://github.com/rust-lang/rust/issues/121097

6 files changed, 7 insertions, 33 deletions

diff --git a/tests/mir-opt/building/enum_cast.bar.built.after.mir b/tests/mir-opt/building/enum_cast.bar.built.after.mir
index 72d0cf5d1e8..0dc6448ffad 100644
--- a/tests/mir-opt/building/enum_cast.bar.built.after.mir
+++ b/tests/mir-opt/building/enum_cast.bar.built.after.mir
@@ -5,16 +5,11 @@ fn bar(_1: Bar) -> usize {
     let mut _0: usize;
     let _2: Bar;
     let mut _3: isize;
-    let mut _4: u8;
-    let mut _5: bool;
 
     bb0: {
         StorageLive(_2);
         _2 = move _1;
         _3 = discriminant(_2);
-        _4 = copy _3 as u8 (IntToInt);
-        _5 = Le(copy _4, const 1_u8);
-        assume(move _5);
         _0 = move _3 as usize (IntToInt);
         StorageDead(_2);
         return;
diff --git a/tests/mir-opt/building/enum_cast.boo.built.after.mir b/tests/mir-opt/building/enum_cast.boo.built.after.mir
index 91e06dc8862..3540a2b1e2e 100644
--- a/tests/mir-opt/building/enum_cast.boo.built.after.mir
+++ b/tests/mir-opt/building/enum_cast.boo.built.after.mir
@@ -5,16 +5,11 @@ fn boo(_1: Boo) -> usize {
     let mut _0: usize;
     let _2: Boo;
     let mut _3: u8;
-    let mut _4: u8;
-    let mut _5: bool;
 
     bb0: {
         StorageLive(_2);
         _2 = move _1;
         _3 = discriminant(_2);
-        _4 = copy _3 as u8 (IntToInt);
-        _5 = Le(copy _4, const 1_u8);
-        assume(move _5);
         _0 = move _3 as usize (IntToInt);
         StorageDead(_2);
         return;
diff --git a/tests/mir-opt/building/enum_cast.far.built.after.mir b/tests/mir-opt/building/enum_cast.far.built.after.mir
index 14eaf344190..da34b7ba6c2 100644
--- a/tests/mir-opt/building/enum_cast.far.built.after.mir
+++ b/tests/mir-opt/building/enum_cast.far.built.after.mir
@@ -5,16 +5,11 @@ fn far(_1: Far) -> isize {
     let mut _0: isize;
     let _2: Far;
     let mut _3: i16;
-    let mut _4: u16;
-    let mut _5: bool;
 
     bb0: {
         StorageLive(_2);
         _2 = move _1;
         _3 = discriminant(_2);
-        _4 = copy _3 as u16 (IntToInt);
-        _5 = Le(copy _4, const 1_u16);
-        assume(move _5);
         _0 = move _3 as isize (IntToInt);
         StorageDead(_2);
         return;
diff --git a/tests/mir-opt/building/enum_cast.offsetty.built.after.mir b/tests/mir-opt/building/enum_cast.offsetty.built.after.mir
index 1c2acbe3023..b84ce0de9a0 100644
--- a/tests/mir-opt/building/enum_cast.offsetty.built.after.mir
+++ b/tests/mir-opt/building/enum_cast.offsetty.built.after.mir
@@ -5,20 +5,11 @@ fn offsetty(_1: NotStartingAtZero) -> u32 {
     let mut _0: u32;
     let _2: NotStartingAtZero;
     let mut _3: isize;
-    let mut _4: u8;
-    let mut _5: bool;
-    let mut _6: bool;
-    let mut _7: bool;
 
     bb0: {
         StorageLive(_2);
         _2 = move _1;
         _3 = discriminant(_2);
-        _4 = copy _3 as u8 (IntToInt);
-        _5 = Ge(copy _4, const 4_u8);
-        _6 = Le(copy _4, const 8_u8);
-        _7 = BitAnd(move _5, move _6);
-        assume(move _7);
         _0 = move _3 as u32 (IntToInt);
         StorageDead(_2);
         return;
diff --git a/tests/mir-opt/building/enum_cast.rs b/tests/mir-opt/building/enum_cast.rs
index 4fb9a27e309..eaf5537e0ab 100644
--- a/tests/mir-opt/building/enum_cast.rs
+++ b/tests/mir-opt/building/enum_cast.rs
@@ -4,6 +4,13 @@
 // EMIT_MIR enum_cast.boo.built.after.mir
 // EMIT_MIR enum_cast.far.built.after.mir
 
+// Previously MIR building included range `Assume`s in the MIR statements,
+// which these tests demonstrated, but now that we have range metadata on
+// parameters in LLVM (in addition to !range metadata on loads) the impact
+// of the extra volume of MIR is worse than its value.
+// Thus these are now about the discriminant type and the cast type,
+// both of which might be different from the backend type of the tag.
+
 enum Foo {
     A,
 }
diff --git a/tests/mir-opt/building/enum_cast.signy.built.after.mir b/tests/mir-opt/building/enum_cast.signy.built.after.mir
index 39b6dfaf005..503c506748f 100644
--- a/tests/mir-opt/building/enum_cast.signy.built.after.mir
+++ b/tests/mir-opt/building/enum_cast.signy.built.after.mir
@@ -5,20 +5,11 @@ fn signy(_1: SignedAroundZero) -> i16 {
     let mut _0: i16;
     let _2: SignedAroundZero;
     let mut _3: i16;
-    let mut _4: u16;
-    let mut _5: bool;
-    let mut _6: bool;
-    let mut _7: bool;
 
     bb0: {
         StorageLive(_2);
         _2 = move _1;
         _3 = discriminant(_2);
-        _4 = copy _3 as u16 (IntToInt);
-        _5 = Ge(copy _4, const 65534_u16);
-        _6 = Le(copy _4, const 2_u16);
-        _7 = BitOr(move _5, move _6);
-        assume(move _7);
         _0 = move _3 as i16 (IntToInt);
         StorageDead(_2);
         return;