vect: Move speculative read check for inbound access
Improves vectorizer's ability to safely speculate accesses in loops with multiple data references.
The check for safe speculative reads when data accesses are within known bounds has been moved to a dedicated loop. Previously, this check could exit early after the first misaligned access, preventing other data references within the same loop from being marked as safe for speculation. This change ensures that all accesses are evaluated correctly, allowing for more aggressive vectorization.
In Details
The DR_SCALAR_KNOWN_BOUNDS check, which determines if a misaligned access can be safely speculated by the vectorizer if all scalar accesses are within a known fixed-size array, was previously placed within a loop that could exit prematurely. This commit moves the check to its own loop within vect_enhance_data_refs_alignment to ensure it correctly evaluates all data references for safe speculation, particularly in cases with multiple misaligned accesses.
- vectorizer
- A compiler component that transforms code to perform the same operation on multiple data elements simultaneously, typically by utilizing special CPU instructions. This can significantly improve performance for data-parallel tasks.
- speculative execution
- A performance optimization technique where a processor or compiler may execute instructions before they are known to be necessary. If the predicted outcome is correct, performance improves; if not, the work is discarded.
- misaligned access
- An attempt to access data in memory at an address that is not a multiple of the data's size. This can lead to performance penalties or even crashes on some architectures.