Handle the case where the or disjoint folds immediately to a constant

compiler/rustc_codegen_llvm/src/builder.rs

@@ -424,7 +424,13 @@ impl<'a, 'll, 'tcx> BuilderMethods<'a, 'tcx> for Builder<'a, 'll, 'tcx> {
     fn or_disjoint(&mut self, a: &'ll Value, b: &'ll Value) -> &'ll Value {
         unsafe {
             let or = llvm::LLVMBuildOr(self.llbuilder, a, b, UNNAMED);
-            llvm::LLVMSetIsDisjoint(or, True);
+
+            // If a and b are both values, then `or` is a value, rather than
+            // an instruction, so we need to check before setting the flag.
+            // (See also `LLVMBuildNUWNeg` which also needs a check.)
+            if llvm::LLVMIsAInstruction(or).is_some() {
+                llvm::LLVMSetIsDisjoint(or, True);
+            }
             or
         }
     }

tests/codegen/intrinsics/disjoint_bitor.rs

@@ -1,4 +1,4 @@
-//@ compile-flags: -C no-prepopulate-passes
+//@ compile-flags: -C no-prepopulate-passes -Z mir-opt-level=0
 
 #![crate_type = "lib"]
 #![feature(core_intrinsics)]
@@ -18,3 +18,13 @@ pub unsafe fn disjoint_bitor_unsigned(x: u64, y: u64) -> u64 {
     // CHECK: or disjoint i64 %x, %y
     disjoint_bitor(x, y)
 }
+
+// CHECK-LABEL: @disjoint_bitor_literal
+#[no_mangle]
+pub unsafe fn disjoint_bitor_literal() -> u8 {
+    // This is a separate check because even without any passes,
+    // LLVM will fold so it's not an instruction, which can assert in LLVM.
+
+    // CHECK: store i8 3
+    disjoint_bitor(1, 2)
+}