Workaround code generation bug in clang

j-naylor · j-naylor · commit f83f14881c7a · 2025-06-16T09:27:15.000+07:00
At optimization level -O0, builds on recent clang fail to produce the correct CRC32C with our AVX-512 implementation. For now, just disable the runtime check for clang at -O0. When this is fixed upstream and we know the extent of the breakage, we can adjust to be version-specific. Reported-by: Soumyadeep Chakraborty <soumyadeep2007@gmail.com> Reported-by: Andy Fan <zhihuifan1213@163.com> Tested-by: Andy Fan <zhihuifan1213@163.com> Discussion: https://postgr.es/m/CAE-ML%2B-OV6p9uvCFBcSQjZUEh__y0h-KjN%2BBseyGJHt7u8EP%2Bw%40mail.gmail.com Discussion: https://postgr.es/m/87o6uqd3iv.fsf%40163.com
diff --git a/src/port/pg_crc32c_sse42_choose.c b/src/port/pg_crc32c_sse42_choose.c
@@ -95,7 +95,9 @@ pg_comp_crc32c_choose(pg_crc32c crc, const void *data, size_t len)
 			__cpuidex(exx, 7, 0);
 #endif
 
-#ifdef USE_AVX512_CRC32C_WITH_RUNTIME_CHECK
+#if defined(__clang__) && !defined(__OPTIMIZE__)
+			/* Some versions of clang are broken at -O0 */
+#elif defined(USE_AVX512_CRC32C_WITH_RUNTIME_CHECK)
 			if (exx[2] & (1 << 10) &&	/* VPCLMULQDQ */
 				exx[1] & (1 << 31)) /* AVX512-VL */
 				pg_comp_crc32c = pg_comp_crc32c_avx512;
