https://bugs.llvm.org/show_bug.cgi?id=33368
Bug ID: 33368
Summary: DAGCombine incorrecly eliminates vector
extension/truncation sequence
Product: libraries
Version: trunk
Hardware: PC
OS: All
Status: NEW
Severity: normal
Priority: P
Component: Common Code Generator Code
Assignee: [email protected]
Reporter: [email protected]
CC: [email protected]
// The following test case (derived from a randomly generated
// case) fails with -O2 (Linux):
typedef char __attribute__((ext_vector_type(2))) char2;
typedef char __attribute__((ext_vector_type(8))) char8;
extern "C" int printf(const char *, ...);
__attribute__((noinline)) void use(char2 c) {
volatile char2 cc = c;
}
__attribute__((noinline)) void test(char8 vec) {
char2 b2 = vec.zxxx.wx;
volatile char2 c2 = b2;
printf("c2:%x %x => ", c2[0], c2[1]);
if (c2[1] == 3)
printf("PASSED\n");
else
printf("FAILED\n");
use(b2);
}
int main() {
char8 vec = {1, 2, 3, 4, 5, 6, 7, 8};
test(vec);
}
// ====== end here ==========
DAGcombine incorrectly eliminates a combination of vector extension/
vector truncation because it only examines the element sizes of the
respective source and target vectors without considering the scales
of extension and truncation. The failing case extends by 2 (i8->i16)
and subsequently truncates by 8 (i64->i8), so the intermediate
operations cannot be eliminated.
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