[Piglit] [PATCH] cl: Add test for MUBUF access with a negative vaddr

[Matt Arsenault]

Explanation in test comment.
---
 .../program/execute/amdgcn-mubuf-negative-vaddr.cl | 62 ++++++++++++++++++++++
 1 file changed, 62 insertions(+)
 create mode 100644 tests/cl/program/execute/amdgcn-mubuf-negative-vaddr.cl

diff --git a/tests/cl/program/execute/amdgcn-mubuf-negative-vaddr.cl b/tests/cl/program/execute/amdgcn-mubuf-negative-vaddr.cl
new file mode 100644
index 000000000..21f11bf66
--- /dev/null
+++ b/tests/cl/program/execute/amdgcn-mubuf-negative-vaddr.cl
@@ -0,0 +1,62 @@
+>/*!
+
+[config]
+name: MUBUF stack addressing behavior
+clc_version_min: 10
+
+[test]
+name: MUBUF negative buffer offsets
+kernel_name: negative_mubuf_vaddr
+dimensions: 1
+global_size: 16 0 0
+
+arg_out: 0 buffer int[16]        \
+  5 5 5 5 \
+  5 5 5 5 \
+  5 5 5 5 \
+  5 5 5 5
+
+!*/
+
+// Prior to gfx9, MUBUF instructions with the vaddr offset enabled
+// would always perform a range check. If a negative vaddr base index
+// was used, this would fail the range check. The overall address
+// computation would compute a valid address, but this doesn't happen
+// due to the range check. For out-of-bounds MUBUF loads, a 0 is
+// returned.
+//
+// Therefore it should be safe to fold any VGPR offset on gfx9 into
+// the MUBUF vaddr, but not on older subtargets which can only do this
+// if the sign bit is known 0.
+kernel void negative_mubuf_vaddr(global int* out0)
+{
+    volatile int array[16];
+
+    int id = get_global_id(0);
+    for (int i = 0; i < 16; ++i)
+    {
+        array[i] = i + 1;
+    }
+
+    // Directly addressing the same buffer address works without using vaddr:
+    //
+    // buffer_load_dword v2, off, s[0:3], s11 offset:20
+    // out0[id] = array[4];
+
+
+    // But having a negative computed base index would fail:
+    // v_mov_b32_e32 v0, -8
+    // v_lshlrev_b32_e32 v0, 2, v0
+    // v_add_i32_e32 v0, vcc, 4, v0
+    // buffer_load_dword v2, v0, s[0:3], s11 offen offset:48
+
+#ifdef __AMDGCN__
+    // Obscure the value so it can't be folded with other constant or
+    // make known bits assumptions.
+    int offset;
+    __asm volatile("v_mov_b32 %0, -8" : "=v"(offset));
+#else
+    int offset = -8;
+#endif
+    out0[id] = array[offset + 12];
+}
-- 
2.11.0