https://bugs.llvm.org/show_bug.cgi?id=50803
Bug ID: 50803
Summary: [SIMD] Compiler unable to vectorize trivial loops
Product: libraries
Version: trunk
Hardware: PC
OS: Windows NT
Status: NEW
Severity: normal
Priority: P
Component: Backend: WebAssembly
Assignee: unassignedb...@nondot.org
Reporter: cl...@evan.coeusgroup.com
CC: llvm-bugs@lists.llvm.org
Here is an example (or on Compiler Explorer: https://godbolt.org/z/5Was18P7r):
#include <stdint.h>
typedef int32_t i32x4 __attribute__((__vector_size__(16)));
i32x4 add(i32x4 a, i32x4 b);
i32x4
add(i32x4 a, i32x4 b) {
i32x4 r;
#pragma clang loop vectorize(enable)
for (int i = 0 ; i < 4 ; i++) {
r[i] = a[i] + b[i];
}
return r;
}
Compile with -msimd128 -O3, no vectorization. The scalar version seems pretty
bad, too.
Even with the pragma the compiler won't vectorize the loop. I'm wondering if
this might have something to do with the -Wconditional-uninitialized diagnostic
emitted when returning r (it's not enabled by default, -Weverything or
-Wconditional-uninitialized to see it).
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