Auto merge of #147541 - saethlin:transmute-carefully, r=scottmcm

Change int-to-ptr transmute lowering back to inttoptr

This is a revert of https://github.com/rust-lang/rust/pull/121282, but with a regression test to cover the reported miscompile in https://github.com/rust-lang/rust/issues/147265 that was caused by the way the code here combines with https://github.com/rust-lang/rust/pull/138759.

compiler/rustc_codegen_ssa/src/mir/rvalue.rs

@@ -1008,14 +1008,14 @@ pub(super) fn transmute_scalar<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>>(
     imm = match (from_scalar.primitive(), to_scalar.primitive()) {
         (Int(..) | Float(_), Int(..) | Float(_)) => bx.bitcast(imm, to_backend_ty),
         (Pointer(..), Pointer(..)) => bx.pointercast(imm, to_backend_ty),
-        (Int(..), Pointer(..)) => bx.ptradd(bx.const_null(bx.type_ptr()), imm),
+        (Int(..), Pointer(..)) => bx.inttoptr(imm, to_backend_ty),
         (Pointer(..), Int(..)) => {
             // FIXME: this exposes the provenance, which shouldn't be necessary.
             bx.ptrtoint(imm, to_backend_ty)
         }
         (Float(_), Pointer(..)) => {
             let int_imm = bx.bitcast(imm, bx.cx().type_isize());
-            bx.ptradd(bx.const_null(bx.type_ptr()), int_imm)
+            bx.inttoptr(int_imm, to_backend_ty)
         }
         (Pointer(..), Float(_)) => {
             // FIXME: this exposes the provenance, which shouldn't be necessary.

tests/codegen-llvm/common_prim_int_ptr.rs

@@ -11,7 +11,7 @@
 #[no_mangle]
 pub fn insert_int(x: usize) -> Result<usize, Box<()>> {
     // CHECK: start:
-    // CHECK-NEXT: %[[WO_PROV:.+]] = getelementptr i8, ptr null, [[USIZE:i[0-9]+]] %x
+    // CHECK-NEXT: %[[WO_PROV:.+]] = inttoptr [[USIZE:i[0-9]+]] %x to ptr
     // CHECK-NEXT: %[[R:.+]] = insertvalue { [[USIZE]], ptr } { [[USIZE]] 0, ptr poison }, ptr %[[WO_PROV]], 1
     // CHECK-NEXT: ret { [[USIZE]], ptr } %[[R]]
     Ok(x)

tests/codegen-llvm/enum/enum-aggregate.rs

@@ -70,7 +70,7 @@ fn make_ok_ptr(x: NonNull<u16>) -> Result<NonNull<u16>, usize> {
 fn make_ok_int(x: usize) -> Result<usize, NonNull<u16>> {
     // CHECK-LABEL: { i64, ptr } @make_ok_int(i64 %x)
     // CHECK-NEXT: start:
-    // CHECK-NEXT: %[[NOPROV:.+]] = getelementptr i8, ptr null, i64 %x
+    // CHECK-NEXT: %[[NOPROV:.+]] = inttoptr i64 %x to ptr
     // CHECK-NEXT: %[[R:.+]] = insertvalue { i64, ptr } { i64 0, ptr poison }, ptr %[[NOPROV]], 1
     // CHECK-NEXT: ret { i64, ptr } %[[R]]
     Ok(x)

tests/codegen-llvm/int-ptr-int-enum-miscompile.rs

@@ -0,0 +1,22 @@
+// This is a regression test for https://github.com/rust-lang/rust/issues/147265.
+
+//@ compile-flags: -Copt-level=3
+
+#![crate_type = "lib"]
+
+#[no_mangle]
+pub fn mk_result(a: usize) -> Result<u8, *const u8> {
+    // CHECK-LABEL: @mk_result
+    // CHECK-NOT: unreachable
+    // CHECK: load i8,
+    // CHECK-NOT: unreachable
+    match g(a) {
+        Ok(b) => Ok(unsafe { *(b as *const u8) }),
+        Err(c) => Err(c),
+    }
+}
+
+#[cold]
+fn g(a: usize) -> Result<usize, *const u8> {
+    Ok(a)
+}

tests/codegen-llvm/intrinsics/transmute-niched.rs

@@ -249,7 +249,7 @@ pub unsafe fn check_four_or_eight_to_nonnull(x: FourOrEight) -> NonNull<u8> {
     // OPT: call void @llvm.assume(i1 %1)
     // CHECK-NOT: icmp
     // CHECK-NOT: assume
-    // CHECK: %[[RET:.+]] = getelementptr i8, ptr null, i64 %x
+    // CHECK: %[[RET:.+]] = inttoptr i64 %x to ptr
     // CHECK-NEXT: ret ptr %[[RET]]
 
     transmute(x)

tests/codegen-llvm/intrinsics/transmute.rs

@@ -303,7 +303,7 @@ pub unsafe fn check_pair_with_bool(x: (u8, bool)) -> (bool, i8) {
 pub unsafe fn check_float_to_pointer(x: f64) -> *const () {
     // CHECK-NOT: alloca
     // CHECK: %0 = bitcast double %x to i64
-    // CHECK: %_0 = getelementptr i8, ptr null, i64 %0
+    // CHECK: %_0 = inttoptr i64 %0 to ptr
     // CHECK: ret ptr %_0
     transmute(x)
 }
@@ -378,7 +378,7 @@ pub unsafe fn check_issue_110005(x: (usize, bool)) -> Option<Box<[u8]>> {
 // CHECK-LABEL: @check_pair_to_dst_ref(
 #[no_mangle]
 pub unsafe fn check_pair_to_dst_ref<'a>(x: (usize, usize)) -> &'a [u8] {
-    // CHECK: %_0.0 = getelementptr i8, ptr null, i64 %x.0
+    // CHECK: %_0.0 = inttoptr i64 %x.0 to ptr
     // CHECK: %0 = icmp ne ptr %_0.0, null
     // CHECK: call void @llvm.assume(i1 %0)
     // CHECK: %1 = insertvalue { ptr, i64 } poison, ptr %_0.0, 0

tests/codegen-llvm/transmute-scalar.rs

@@ -56,7 +56,7 @@ pub fn ptr_to_int(p: *mut u16) -> usize {
 }
 
 // CHECK: define{{.*}}ptr @int_to_ptr([[USIZE]] %i)
-// CHECK: %_0 = getelementptr i8, ptr null, [[USIZE]] %i
+// CHECK: %_0 = inttoptr [[USIZE]] %i to ptr
 // CHECK-NEXT: ret ptr %_0
 #[no_mangle]
 pub fn int_to_ptr(i: usize) -> *mut u16 {