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From: "bettio.davide at gmail dot com" <gcc-bugzilla@gcc.gnu.org> To: gcc-bugs@gcc.gnu.org Subject: [Bug c/111933] New: memcpy on Xtensa not optimized when n == sizeof(uint32_t) or sizeof(uint64_t) Date: Mon, 23 Oct 2023 11:16:12 +0000 [thread overview] Message-ID: <bug-111933-4@http.gcc.gnu.org/bugzilla/> (raw) https://gcc.gnu.org/bugzilla/show_bug.cgi?id=111933 Bug ID: 111933 Summary: memcpy on Xtensa not optimized when n == sizeof(uint32_t) or sizeof(uint64_t) Product: gcc Version: 11.2.0 Status: UNCONFIRMED Severity: normal Priority: P3 Component: c Assignee: unassigned at gcc dot gnu.org Reporter: bettio.davide at gmail dot com Target Milestone: --- This issue is about what I think being a missing optimization on ESP32 Xtensa GCC compiler. I tested the same issue on versions between gcc 8.4.0 and 11.2.0 with Xtensa ESP32/ESP32-S2/ESP32-S3 GCC. I'm writing some functions for unaligned memory access and I've been checking them with Compiler Explorer (https://godbolt.org/) and I'm getting some (I think) sub-optimal outputs. As far as I understood on ESP32 Xtensa a 32-bit unaligned memory access is faster than 4 8-bit accesses, however I'm getting the following results (using -O2) and the following snippets of code: Function that calls the inline from_unaligned_u32: bool test2(uint32_t *in) { uint32_t got = from_unaligned_u32(in); if (got > 5) { return true; } return false; } A: uint32_t from_unaligned_u32(uint32_t *unaligned) { uint32_t tmp; tmp = *unaligned; return tmp; } generates: test2(unsigned int*): entry sp, 32 l32i.n a8, a2, 0 movi.n a2, 1 bgeui a8, 6, .L2 movi.n a2, 0 .L2: extui a2, a2, 0, 1 retw.n B: inline uint32_t from_unaligned_u32(uint32_t *unaligned) { uint32_t tmp; memcpy(&tmp, unaligned, sizeof(tmp)); return tmp; } generates: test2(unsigned int*): entry sp, 48 l8ui a8, a2, 2 l8ui a10, a2, 0 l8ui a9, a2, 1 l8ui a2, a2, 3 s8i a10, sp, 0 s8i a2, sp, 3 s8i a9, sp, 1 s8i a8, sp, 2 l32i.n a8, sp, 0 movi.n a2, 1 bgeui a8, 6, .L2 movi.n a2, 0 .L2: extui a2, a2, 0, 1 retw.n My assumption here is that unaligned access on Xtensa ESP32 is faster than calling memcpy or multiple 1-byte loads (please let me know if I am wrong), so from my point of view is a missing optimization. I would expect both A and B generating the same assembly code like on other archs. Also interstingly the uint64_t "B" version (that is similar to the previous), generates a call to memcpy instead of some inline code.
next reply other threads:[~2023-10-23 11:16 UTC|newest] Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top 2023-10-23 11:16 bettio.davide at gmail dot com [this message] 2023-10-23 13:37 ` [Bug middle-end/111933] " rguenth at gcc dot gnu.org 2023-10-23 13:54 ` bettio.davide at gmail dot com
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