fix GVN trying to transmute pointers to integers

3 files changed, 31 insertions, 15 deletions

diff --git a/compiler/rustc_mir_transform/src/gvn.rs b/compiler/rustc_mir_transform/src/gvn.rs
index 50c9702cb9b..7707d0d51f1 100644
--- a/compiler/rustc_mir_transform/src/gvn.rs
+++ b/compiler/rustc_mir_transform/src/gvn.rs
@@ -103,7 +103,7 @@ use rustc_middle::ty::layout::{HasParamEnv, LayoutOf};
 use rustc_middle::ty::{self, Ty, TyCtxt};
 use rustc_span::DUMMY_SP;
 use rustc_span::def_id::DefId;
-use rustc_target::abi::{self, Abi, FIRST_VARIANT, FieldIdx, Size, VariantIdx};
+use rustc_target::abi::{self, Abi, FIRST_VARIANT, FieldIdx, Primitive, Size, VariantIdx};
 use smallvec::SmallVec;
 use tracing::{debug, instrument, trace};
 
@@ -568,13 +568,29 @@ impl<'body, 'tcx> VnState<'body, 'tcx> {
                 CastKind::Transmute => {
                     let value = self.evaluated[value].as_ref()?;
                     let to = self.ecx.layout_of(to).ok()?;
-                    // `offset` for immediates only supports scalar/scalar-pair ABIs,
-                    // so bail out if the target is not one.
+                    // `offset` for immediates generally only supports projections that match the
+                    // type of the immediate. However, as a HACK, we exploit that it can also do
+                    // limited transmutes: it only works between types with the same layout, and
+                    // cannot transmute pointers to integers.
                     if value.as_mplace_or_imm().is_right() {
-                        match (value.layout.abi, to.abi) {
-                            (Abi::Scalar(..), Abi::Scalar(..)) => {}
-                            (Abi::ScalarPair(..), Abi::ScalarPair(..)) => {}
-                            _ => return None,
+                        let can_transmute = match (value.layout.abi, to.abi) {
+                            (Abi::Scalar(s1), Abi::Scalar(s2)) => {
+                                s1.size(&self.ecx) == s2.size(&self.ecx)
+                                    && !matches!(s1.primitive(), Primitive::Pointer(..))
+                            }
+                            (Abi::ScalarPair(a1, b1), Abi::ScalarPair(a2, b2)) => {
+                                a1.size(&self.ecx) == a2.size(&self.ecx) &&
+                                b1.size(&self.ecx) == b2.size(&self.ecx) &&
+                                // The alignment of the second component determines its offset, so that also needs to match.
+                                b1.align(&self.ecx) == b2.align(&self.ecx) &&
+                                // None of the inputs may be a pointer.
+                                !matches!(a1.primitive(), Primitive::Pointer(..))
+                                    && !matches!(b1.primitive(), Primitive::Pointer(..))
+                            }
+                            _ => false,
+                        };
+                        if !can_transmute {
+                            return None;
                         }
                     }
                     value.offset(Size::ZERO, to, &self.ecx).discard_err()?
diff --git a/tests/coverage/closure_macro.cov-map b/tests/coverage/closure_macro.cov-map
index eb5f94d1080..fb4a137d4c8 100644
--- a/tests/coverage/closure_macro.cov-map
+++ b/tests/coverage/closure_macro.cov-map
@@ -23,19 +23,19 @@ Number of file 0 mappings: 6
 - Code(Counter(0)) at (prev + 3, 1) to (start + 0, 2)
 
 Function name: closure_macro::main::{closure#0}
-Raw bytes (35): 0x[01, 01, 03, 01, 05, 05, 0b, 09, 00, 05, 01, 10, 1c, 03, 21, 05, 04, 11, 01, 27, 02, 03, 11, 00, 16, 00, 00, 17, 00, 1e, 07, 02, 09, 00, 0a]
+Raw bytes (35): 0x[01, 01, 03, 01, 05, 05, 0b, 09, 0d, 05, 01, 10, 1c, 03, 21, 05, 04, 11, 01, 27, 02, 03, 11, 00, 16, 0d, 00, 17, 00, 1e, 07, 02, 09, 00, 0a]
 Number of files: 1
 - file 0 => global file 1
 Number of expressions: 3
 - expression 0 operands: lhs = Counter(0), rhs = Counter(1)
 - expression 1 operands: lhs = Counter(1), rhs = Expression(2, Add)
-- expression 2 operands: lhs = Counter(2), rhs = Zero
+- expression 2 operands: lhs = Counter(2), rhs = Counter(3)
 Number of file 0 mappings: 5
 - Code(Counter(0)) at (prev + 16, 28) to (start + 3, 33)
 - Code(Counter(1)) at (prev + 4, 17) to (start + 1, 39)
 - Code(Expression(0, Sub)) at (prev + 3, 17) to (start + 0, 22)
     = (c0 - c1)
-- Code(Zero) at (prev + 0, 23) to (start + 0, 30)
+- Code(Counter(3)) at (prev + 0, 23) to (start + 0, 30)
 - Code(Expression(1, Add)) at (prev + 2, 9) to (start + 0, 10)
-    = (c1 + (c2 + Zero))
+    = (c1 + (c2 + c3))
 
diff --git a/tests/coverage/closure_macro_async.cov-map b/tests/coverage/closure_macro_async.cov-map
index 4d0597f58bf..091e87909f9 100644
--- a/tests/coverage/closure_macro_async.cov-map
+++ b/tests/coverage/closure_macro_async.cov-map
@@ -31,19 +31,19 @@ Number of file 0 mappings: 6
 - Code(Counter(0)) at (prev + 3, 1) to (start + 0, 2)
 
 Function name: closure_macro_async::test::{closure#0}::{closure#0}
-Raw bytes (35): 0x[01, 01, 03, 01, 05, 05, 0b, 09, 00, 05, 01, 15, 1c, 03, 21, 05, 04, 11, 01, 27, 02, 03, 11, 00, 16, 00, 00, 17, 00, 1e, 07, 02, 09, 00, 0a]
+Raw bytes (35): 0x[01, 01, 03, 01, 05, 05, 0b, 09, 0d, 05, 01, 15, 1c, 03, 21, 05, 04, 11, 01, 27, 02, 03, 11, 00, 16, 0d, 00, 17, 00, 1e, 07, 02, 09, 00, 0a]
 Number of files: 1
 - file 0 => global file 1
 Number of expressions: 3
 - expression 0 operands: lhs = Counter(0), rhs = Counter(1)
 - expression 1 operands: lhs = Counter(1), rhs = Expression(2, Add)
-- expression 2 operands: lhs = Counter(2), rhs = Zero
+- expression 2 operands: lhs = Counter(2), rhs = Counter(3)
 Number of file 0 mappings: 5
 - Code(Counter(0)) at (prev + 21, 28) to (start + 3, 33)
 - Code(Counter(1)) at (prev + 4, 17) to (start + 1, 39)
 - Code(Expression(0, Sub)) at (prev + 3, 17) to (start + 0, 22)
     = (c0 - c1)
-- Code(Zero) at (prev + 0, 23) to (start + 0, 30)
+- Code(Counter(3)) at (prev + 0, 23) to (start + 0, 30)
 - Code(Expression(1, Add)) at (prev + 2, 9) to (start + 0, 10)
-    = (c1 + (c2 + Zero))
+    = (c1 + (c2 + c3))