Compiler Bugs

SIMDe has proven to be rather good at finding compiler bugs.

It is generally possible for us to work around these issues, usually by using the preprocessor to choose a different code path. When we find bugs in the current versions of compilers we try to report them so they can be fixed; the GCC and Emscripten developers in particular have been very responsive and helpful.

Bugs We Can't Work Around

Unfortunately, sometimes working around a bug simply isn't feasible. What follows is a list of bugs we can't currently work around.

Clang

• Clang 3.8 hits an internal compiler error when trying to auto-vectorize some functions using AVX-512VL. This isn't usually a problem outside of our test suite since if AVX-512VL is enabled SIMDe will typically use the AVX-512VL intrinsics instead of auto-vectorizing. Either upgrade to clang 3.9, don't use -DSIMDE_NO_NATIVE (which is really only for testing), or don't auto-vectorize to AVX-512VL (don't use -mavx512vl or add -mno-avx512vl).

GCC

• All GCC 7.x releases hit a floating point exception internal compiler error when compiling many AVX-512 functions if optimization is enabled (-O1 or higher), debugging is enabled (-g), and AVX is not enabled. For details, see issue #278. This only effects applications which use the SIMDe versions of certain AVX-512 instructions.
• GCC 4.7 - 5 don't work reliably with AVX-512 support as many functions will generate internal compiler errors. You can still use there compilers with SIMDe, just don't pass -mavx512f (or otherwise enable it, such as with -march=native on an AVX-512 machine) or pass -mno-avx512f.

PGI

• PGI doesn't work in C++ mode. PGI is tracking the issue internally as TPR #28482. For details, see their community forum

Bugs Discovered By SIMDe

As mentioned in the introduction, we seem to find a fair number of compiler bugs. What follows is an incomplete list of some of the issues we've found in compilers which have been fixed, and/or for which there is a work-around in SIMDe.

Compiler	Bug	Present In	Fixed In	Type	Description
GCC	95227			Spurious warning	vec_extract doesn't mark input as used in C++ mode
GCC	95239	10 11 12	10.5 12.3 13	Spurious warning	Unable to ignore -Wattribute-warning in macro
GCC	95421			API missing / incorrect	[AArch64] Missing NEON functions documented on ARM's web site
GCC	95471			API missing / incorrect	[ARMv8] vrndvq_f32 defined even when not supported by ARMv8
GCC	95782			ICE	[ppc64le] ICE in _cpp_pop_context
GCC	97016			API missing / incorrect	_MM_CMPINT_ENUM type is missing
GCC	95483		11	API missing / incorrect	[i386] Missing SIMD functions.
GCC	95399			API missing / incorrect	[ARM] 32/64-bit vcvtnq_* functions are missing
GCC	96313		8.5	API missing / incorrect	[AArch64] vqmovun* return types should be unsigned.
GCC	94482	8 / 9	8.5/9.4/10	Incorrect optimization	[8/9 Regression] Inserting into vector with optimization enabled on x86 generates incorrect result.
GCC	93557		9.3/10.1	Spurious warning	__builtin_convertvector doesn't mark input as used.
GCC	94385		9.4/10.1	ICE	[10 Regression] Internal compiler error for __builtin_convertvector + statement expr. Latent bug in GCC 9.
GCC	94488		8.5/9.4/10.1	ICE	[AArch64] ICE on right shift of V2DImode by DImode shift.
GCC	96174		9.4/10.2	API missing / incorrect	AVX-512 functions missing when compiled without optimization.
GCC	98428	11	11.1	ICE	ICE with omp simd loop + optimization
GCC	98521	10.2.1	10.3	API missing / incorrect	[x86] _mm256_cmov_si256 XOP function is missing.
GCC	97248			ICE	[mips] unrecognizable insn when left shifting uint64 vector by scalar with MSA
GCC	99754	11 12	11.4 12.1	API missing / incorrect	[sse2] new _mm_loadu_si16 and _mm_loadu_si32 implemented incorrectly
GCC	100760	10.2	12.1	ICE	[mips + msa] ICE: maximum number of generated reload insns per insn achieved
GCC	100761	10.2	12.1	ICE	[mips+msa] ICE when using __builtin_convertvector to convert from u8x8 to u8x16
GCC	100762	10.2	12.1	ICE	[mips+msa] ICE when comparing 64 bit vectors
GCC	100927	10.2		Incorrect optimization	[sse2] floating point to integer conversion functions incorrect results w/ NaN constants + optimization
GCC	105339	9, 10, 11, 12	9.5, 10.4, 11.4, 12.1	API missing / incorrect	[x86] missing AVX-512F scalef functions when optimization is disabled
GCC	101714	10.2.1	12.1	Implementation incorrect	[POWER] vec_min / vec_max handles NaN incorrectly when evaluated at compile time
GCC	101985	9, 10, 11	12.0	Implementation incorrect	[POWER] vec_cpsgn parameter order was reversed
Clang	BZ45541 GH44886		15.0	Incorrect optimization	[AArch64] Incorrect result for vector conversion with -O2
Clang	45931		11	API missing / incorrect	Many AVX-512 functions take an int instead of unsigned int.
Clang	BZ45959 GH45304			Spurious warning	SIMD & reduction on signed types emits sign-conversion diagnostic
Clang	BZ46770 GH46114		12	API missing / incorrect	[ppc] vec_sel variants missing
Clang	46844		12 (AArch64-only)	Incorrect optimization	[AArch64] incorrect results from vcvt* functions with negative inputs when optimization is enabled.
Clang	46840		12	API missing / incorrect	[AArch64] vqmovun* return types should be unsigned.
Clang	32827			API missing / incorrect	_mm_set_pd1 missing from emmintrin.h
Clang	44589			Spurious warning	_mm_extract_pi16 and _mm_insert_pi16 warn with -Wvector-conversion. Fixed in clang 11.0
Clang	BZ48257 GH47601			Spurious warning	vget_lane_p64 triggers -Wvector-conversion diagnostic
Clang	BZ48673 GH48017			API missing / incorrect	[x86] _mm_frcz_ss and _mm_frcz_sd should take two parameters
Clang	48718		12	API missing / incorrect	NEON scalar comparison functions should return unsigned values
Clang	49716	7+	13	ICE	clang segfault at -O2 in C mode
Clang	BZ50893 GH50237	11.0	13.0	ICE	Compiler error when converting from vector of 2x32 to 2x64-bit int on POWER7
Clang	BZ50901 GH50245	11.0	13.0	ICE	[power7] error in backend: Cannot select v16i8 = PPCISD::SCALAR_TO_VECTOR_PERMUTED
Clang	BZ50905 GH50249	11.0		Perf	slow code for absolute value of int8 x 16 vector on POWER9 at -O3
Clang	BZ50932 GH50276		14.0	API missing / incorrect	[POWER] vec_bperm missing documented signatures
Clang	51992	14-dev	14-dev	ICE	Regression [VectorCombine] ScalarizationResult destructor assertion due to SafeWithFreeze and scalarizeLoadExtract
Clang	71362			Incorrect Implementation	NEON intrinsic compilation error occurs when using -fno-lax-vector-conversions
Clang	71365			Incorrect Implementation	Wrong return type in some ARM NEON intrinsics
Clang	71751	15		API missing / incorrect	Wrong return type of NEON intrinsic vqrshrunh_n_s16 in arm_neon.h
Clang	71763			Incorrect Implementation	Wrong result of NEON intrinsic vld2q_dup_p16 with -march=armv7-a
Emscripten	10425			ICE	LLVM assertion failure when casting a SIMD type with -O3
Emscripten	11315			ICE	Crash in WebAssembly Register Stackify with tot
Emscripten	11176			ICE	"Not a vector MVT!" clang error with -s SIMD=1 on tot
Emscripten	10563			ICE	emcc crashes with SIMD without optimization
Emscripten	10651			API missing / incorrect	emscripten errors in wasm_simd128.h
Emscripten	14629			ICE	UNREACHABLE executed at …/binaryen/src/wasm-interpreter.h:503!
Emscripten	19179			API incorrect	Compiler advertises __builtin_roundeven{f,} but it is not implemented
ICC	???			Incorrect optimization	ICC generates incorrect code for signed absolute difference
ICC	???			False advertisement of feature	__builtin_expect_with_probability unsupported but __has_builtin claims otherwise
ICC	???			False advertisement of feature	fallthrough attribute unsupported, contrary to icc's claims
ICC	???			ICE	Internal error: 04010002_1671
NVC	30104	21.3		ICE	ICE from % operator on vector extensions
NVC	30107	21.3		ICE	Using _mm_cvtpd_epi32 results in compiler error
NVC	30106	21.3		API missing/incorrect	Undefined reference to `__builtin_ia32_palignr256’ when calling _mm256_alignr_epi8

Note: some of the version number information may be incorrect or missing. Sorry, it's a recent addition to the table.