Add debug checks to const gep argument bit sizes to resolve TheDan64#213

src/values/ptr_value.rs

@@ -68,7 +68,17 @@ impl<'ctx> PointerValue<'ctx> {
 
     // REVIEW: Should this be on array value too?
     /// GEP is very likely to segfault if indexes are used incorrectly, and is therefore an unsafe function. Maybe we can change this in the future.
+    /// GEP indexes must be 32 bit integer values. Constant folding may result in other sizes working.
     pub unsafe fn const_gep(self, ordered_indexes: &[IntValue<'ctx>]) -> PointerValue<'ctx> {
+        if cfg!(debug_assertions) {
+            for (index, value) in ordered_indexes.iter().enumerate() {
+                let bit_width = value.get_type().get_bit_width();
+                if bit_width != 32 {
+                    panic!("Index #{} in ordered_indexes argument to const_gep call was a {} bit integer instead of 32 bit integer - gep indexes must be i32 values", index, bit_width);
+                }
+            }
+        }
+
         let mut index_values: Vec<LLVMValueRef> = ordered_indexes.iter()
                                                                  .map(|val| val.as_value_ref())
                                                                  .collect();
@@ -80,7 +90,17 @@ impl<'ctx> PointerValue<'ctx> {
     }
 
     /// GEP is very likely to segfault if indexes are used incorrectly, and is therefore an unsafe function. Maybe we can change this in the future.
+    /// GEP indexes must be 32 bit integer values. Constant folding may result in other sizes working.
     pub unsafe fn const_in_bounds_gep(self, ordered_indexes: &[IntValue<'ctx>]) -> PointerValue<'ctx> {
+        if cfg!(debug_assertions) {
+            for (index, value) in ordered_indexes.iter().enumerate() {
+                let bit_width = value.get_type().get_bit_width();
+                if bit_width != 32 {
+                    panic!("Index #{} in ordered_indexes argument to const_in_bounds_gep call was a {} bit integer instead of 32 bit integer - gep indexes must be i32 values", index, bit_width);
+                }
+            }
+        }
+
         let mut index_values: Vec<LLVMValueRef> = ordered_indexes.iter()
                                                                  .map(|val| val.as_value_ref())
                                                                  .collect();

tests/all/test_values.rs

@@ -1203,3 +1203,30 @@ fn test_constant_expression() {
     assert!(expr.is_const());
     assert!(!expr.is_constant_int());
 }
+
+#[test]
+#[should_panic]
+fn test_const_gep_i64() {
+    let context = Context::create();
+
+    let i64_type = context.i64_type();
+    let i64_ptr_type = i64_type.ptr_type(AddressSpace::Generic);
+    let i64_ptr_null = i64_ptr_type.const_zero();
+    unsafe {
+        // i64 indexes are not permitted - should panic.
+        i64_ptr_null.const_gep(&[i64_type.const_zero()]);
+    }
+}
+
+#[test]
+fn test_const_gep_i32() {
+    let context = Context::create();
+
+    let i32_type = context.i32_type();
+    let i32_ptr_type = i32_type.ptr_type(AddressSpace::Generic);
+    let i32_ptr_null = i32_ptr_type.const_zero();
+    unsafe {
+        // i32 indexes are permitted.
+        i32_ptr_null.const_gep(&[i32_type.const_zero()]);
+    }
+}