intel/ir: Fix invalid type aliasing with undefined behavior in test_eu_compact.

test_fuzz_compact_instruction() was attempting to modify the uint64_t
data array of a brw_inst through a pointer to uint32_t, which has
undefined behavior.  This was causing the test_eu_compact unit test to
fail mysteriously for me on GCC 7 with some additional
harmless-looking changes I had applied to my tree, which happened to
affect the order instructions are emitted by GCC causing the bit
twiddling to be done after the clear_pad_bits() call which is supposed
to overwrite the same data through a pointer of different type,
leading to data corruption.  A similar failure has been reported by
Vinson Lee on the master branch built with GCC 8.

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=105052
Tested-by: Vinson Lee <vlee@freedesktop.org>
Reviewed-by: Matt Turner <mattst88@gmail.com>

diff --git a/src/intel/compiler/test_eu_compact.cpp b/src/intel/compiler/test_eu_compact.cpp
index 1532e3b9840709d08ab4e5fae43cb6e788a726d1..f6924abd368228b07fc5c1fdc76a784e493f2cd9 100644 (file)
--- a/src/intel/compiler/test_eu_compact.cpp
+++ b/src/intel/compiler/test_eu_compact.cpp
@@ -149,13 +149,13 @@ test_fuzz_compact_instruction(struct brw_codegen *p, brw_inst src)
 
       for (int bit1 = 0; bit1 < 128; bit1++) {
          brw_inst instr = src;
-        uint32_t *bits = (uint32_t *)&instr;
+        uint64_t *bits = instr.data;
 
          if (skip_bit(p->devinfo, &src, bit1))
            continue;
 
-        bits[bit0 / 32] ^= (1 << (bit0 & 31));
-        bits[bit1 / 32] ^= (1 << (bit1 & 31));
+        bits[bit0 / 64] ^= (1ull << (bit0 & 63));
+        bits[bit1 / 64] ^= (1ull << (bit1 & 63));
 
          clear_pad_bits(p->devinfo, &instr);