Disable jump threading of float equality

compiler/rustc_mir_transform/src/jump_threading.rs

@@ -509,6 +509,13 @@ impl<'tcx, 'a> TOFinder<'tcx, 'a> {
                     BinOp::Ne => ScalarInt::FALSE,
                     _ => return None,
                 };
+                if value.const_.ty().is_floating_point() {
+                    // Floating point equality does not follow bit-patterns.
+                    // -0.0 and NaN both have special rules for equality,
+                    // and therefore we cannot use integer comparisons for them.
+                    // Avoid handling them, though this could be extended in the future.
+                    return None;
+                }
                 let value = value.const_.normalize(self.tcx, self.param_env).try_to_scalar_int()?;
                 let conds = conditions.map(self.arena, |c| Condition {
                     value,

tests/mir-opt/jump_threading.floats.JumpThreading.panic-abort.diff

@@ -0,0 +1,59 @@
+- // MIR for `floats` before JumpThreading
++ // MIR for `floats` after JumpThreading
+
+  fn floats() -> u32 {
+      let mut _0: u32;
+      let _1: f64;
+      let mut _2: bool;
+      let mut _3: bool;
+      let mut _4: f64;
+      scope 1 {
+          debug x => _1;
+      }
+
+      bb0: {
+          StorageLive(_1);
+          StorageLive(_2);
+          _2 = const true;
+-         switchInt(move _2) -> [0: bb2, otherwise: bb1];
++         goto -> bb1;
+      }
+
+      bb1: {
+          _1 = const -0f64;
+          goto -> bb3;
+      }
+
+      bb2: {
+          _1 = const 1f64;
+          goto -> bb3;
+      }
+
+      bb3: {
+          StorageDead(_2);
+          StorageLive(_3);
+          StorageLive(_4);
+          _4 = _1;
+          _3 = Eq(move _4, const 0f64);
+          switchInt(move _3) -> [0: bb5, otherwise: bb4];
+      }
+
+      bb4: {
+          StorageDead(_4);
+          _0 = const 0_u32;
+          goto -> bb6;
+      }
+
+      bb5: {
+          StorageDead(_4);
+          _0 = const 1_u32;
+          goto -> bb6;
+      }
+
+      bb6: {
+          StorageDead(_3);
+          StorageDead(_1);
+          return;
+      }
+  }
+

tests/mir-opt/jump_threading.floats.JumpThreading.panic-unwind.diff

@@ -0,0 +1,59 @@
+- // MIR for `floats` before JumpThreading
++ // MIR for `floats` after JumpThreading
+
+  fn floats() -> u32 {
+      let mut _0: u32;
+      let _1: f64;
+      let mut _2: bool;
+      let mut _3: bool;
+      let mut _4: f64;
+      scope 1 {
+          debug x => _1;
+      }
+
+      bb0: {
+          StorageLive(_1);
+          StorageLive(_2);
+          _2 = const true;
+-         switchInt(move _2) -> [0: bb2, otherwise: bb1];
++         goto -> bb1;
+      }
+
+      bb1: {
+          _1 = const -0f64;
+          goto -> bb3;
+      }
+
+      bb2: {
+          _1 = const 1f64;
+          goto -> bb3;
+      }
+
+      bb3: {
+          StorageDead(_2);
+          StorageLive(_3);
+          StorageLive(_4);
+          _4 = _1;
+          _3 = Eq(move _4, const 0f64);
+          switchInt(move _3) -> [0: bb5, otherwise: bb4];
+      }
+
+      bb4: {
+          StorageDead(_4);
+          _0 = const 0_u32;
+          goto -> bb6;
+      }
+
+      bb5: {
+          StorageDead(_4);
+          _0 = const 1_u32;
+          goto -> bb6;
+      }
+
+      bb6: {
+          StorageDead(_3);
+          StorageDead(_1);
+          return;
+      }
+  }
+

tests/mir-opt/jump_threading.rs

@@ -521,6 +521,16 @@ fn aggregate_copy() -> u32 {
     if c == 2 { b.0 } else { 13 }
 }
 
+fn floats() -> u32 {
+    // CHECK-LABEL: fn floats(
+    // CHECK: switchInt(
+
+    // Test for issue #128243, where float equality was assumed to be bitwise.
+    // When adding float support, it must be ensured that this continues working properly.
+    let x = if true { -0.0 } else { 1.0 };
+    if x == 0.0 { 0 } else { 1 }
+}
+
 fn main() {
     // CHECK-LABEL: fn main(
     too_complex(Ok(0));
@@ -535,6 +545,7 @@ fn main() {
     disappearing_bb(7);
     aggregate(7);
     assume(7, false);
+    floats();
 }
 
 // EMIT_MIR jump_threading.too_complex.JumpThreading.diff
@@ -550,3 +561,4 @@ fn main() {
 // EMIT_MIR jump_threading.aggregate.JumpThreading.diff
 // EMIT_MIR jump_threading.assume.JumpThreading.diff
 // EMIT_MIR jump_threading.aggregate_copy.JumpThreading.diff
+// EMIT_MIR jump_threading.floats.JumpThreading.diff