Add compile test for constant memory overflow detection

Author: PMQ9

tests/compiletests/ui/lang/consts/constant_memory_overflow.rs

@@ -0,0 +1,21 @@
+// Test that automatic constant memory placement fails when exceeding the 64KB limit
+// This test creates multiple large static arrays that together exceed the limit
+
+// compile-flags: -Cllvm-args=--use-constant-memory-space
+
+#![no_std]
+use cuda_std::*;
+
+// 35KB per array, 3 arrays = 105KB total (well above 64KB limit)
+const ARRAY_SIZE: usize = 35 * 1024 / 4;
+
+// NO explicit address_space - let the automatic placement handle it
+// With use_constant_memory_space=true, these should try to go to constant memory
+static BIG_ARRAY_1: [u32; ARRAY_SIZE] = [111u32; ARRAY_SIZE];
+static BIG_ARRAY_2: [u32; ARRAY_SIZE] = [222u32; ARRAY_SIZE];
+static BIG_ARRAY_3: [u32; ARRAY_SIZE] = [333u32; ARRAY_SIZE];
+
+#[kernel]
+pub unsafe fn test_kernel(out: *mut u32) {
+    *out = BIG_ARRAY_1[0] + BIG_ARRAY_2[0] + BIG_ARRAY_3[0];
+}

tests/compiletests/ui/lang/consts/constant_memory_overflow.stderr

@@ -0,0 +1,15 @@
+error: cannot place static `BIG_ARRAY_2` (35840 bytes) in constant memory: cumulative constant memory usage would be 71680 bytes, exceeding the 65536 byte limit
+  --> $DIR/constant_memory_overflow.rs:15:1
+   |
+LL | static BIG_ARRAY_2: [u32; ARRAY_SIZE] = [222u32; ARRAY_SIZE];
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ this static would cause total usage to exceed 65536 bytes
+   |
+   = note: current constant memory usage: 35840 bytes
+   = note: static size: 35840 bytes
+   = note: would result in: 71680 bytes total
+   = help: move this or other statics to global memory using `#[cuda_std::address_space(global)]`
+   = help: reduce the total size of static data
+   = help: disable automatic constant memory placement by setting `.use_constant_memory_space(false)` on `CudaBuilder` in build.rs
+
+error: aborting due to 1 previous error
+