[x86] crash and fail to match pmaddwd #49060
Comments
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This should prevent the crashing: But we want the output to be a "pmaddwd" instruction? |
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The matching code for this pattern was translated from a different/existing pattern here: But it looks like we need to make more adjustments - extract subvector, not truncate? Also possible that the inputs are shorter vectors than the output? |
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Is the "sizeof sizeof(r_)" in the for loop a mistake in your code that exposed the bug? It doesn't logically make sense. |
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More pmadd matching: |
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Resolving as fixed. I added a test based on Craig's suggestion in https://reviews.llvm.org/D99531 that shows we could go even further to try to match pmadd, so if there's a real-world need for that, please file another bug. |
Extended Description
Here is a reduced test case:
#include <stdlib.h>
typedef union {
int16_t i16 attribute((vector_size(32)));
int32_t i32 attribute((vector_size(32)));
} simde__m256i_private;
simde__m256i_private simde__m256i_to_private();
int simde_mm256_madd_epi16() {
simde__m256i_private r_, a_ = simde__m256i_to_private(),
b_ = simde__m256i_to_private();
for (size_t i = 0; i < sizeof sizeof(r_); i += 2)
r_.i32[i] = a_.i16[i] * b_.i16[i] + a_.i16[i + 1] * b_.i16[i + 1];
simde__m256i_from_private(r_);
}
Compile with -O2 using clang (clang++ works) on x86_64. Godbolt link: https://godbolt.org/z/71o5hdY4h
The problem only manifests in my codebase with clang 12, but this test case seems to reliably reproduce the issue in earlier versions as well (back to 7 on godbolt).
I'm also attaching the original (non-reduced) source. Please let me know if you need any additional information.
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