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Demonstrate compiler bug with slice_test (windows opt) #20554

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Demonstrate compiler bug with slice_test (windows opt) #20554

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caba5e6
scary "fix" for slice_test on windows bazel opt
jtattermusch Oct 10, 2019
a2116c5
progress
jtattermusch Oct 10, 2019
ccd0295
reproduce compiler bug
jtattermusch Oct 10, 2019
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26 changes: 25 additions & 1 deletion test/core/slice/slice_test.cc
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Original file line number Diff line number Diff line change
Expand Up @@ -237,13 +237,37 @@ static void test_slice_from_copied_string_works(void) {
grpc_slice_unref(slice);
}

// optimizer doesn't see inside this function
void print_slice(grpc_slice slice)
{
gpr_log(GPR_ERROR, "slice start ptr: %p", GRPC_SLICE_START_PTR(slice));
}

static void test_slice_interning(void) {
LOG_TEST_NAME("test_slice_interning");

grpc_init();
grpc_slice src1 = grpc_slice_from_copied_string("hello123456789123456789");
grpc_slice src2 = grpc_slice_from_copied_string("hello123456789123456789");
GPR_ASSERT(GRPC_SLICE_START_PTR(src1) != GRPC_SLICE_START_PTR(src2));

// the original assert checks that newly allocated slices point to different data
// GPR_ASSERT(GRPC_SLICE_START_PTR(src1) != GRPC_SLICE_START_PTR(src2));

if (GRPC_SLICE_START_PTR(src1) == GRPC_SLICE_START_PTR(src2)) {
gpr_log(GPR_ERROR, "assertion would have failed");
gpr_log(GPR_ERROR, "we just evaluated the start ptrs as being equal, but it's actually not true");
// we want to print the actual values of slice_start_ptr to catch the compiler red-handed
// but we need to be sneaky and look at the values from a different function (outside of the optimizer's sight),
// otherwise the internal state in the compiler changes and we won't trigger the suspected compiler bug.
print_slice(src1);
print_slice(src2);

// If you uncomment the next line, compiler will see that we're using the src1 value and
// the enclosing if statement will be evaluated correctly (pointers will be seen as not equal)
// gpr_log(GPR_ERROR, "src1 start ptr:", GRPC_SLICE_START_PTR(src1));
abort();
}

grpc_slice interned1 = grpc_slice_intern(src1);
grpc_slice interned2 = grpc_slice_intern(src2);
GPR_ASSERT(GRPC_SLICE_START_PTR(interned1) ==
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