I have discovered an issue by accident.
$ lscpu Architecture: x86_64 CPU op-mode(s): 32-bit, 64-bit Byte Order: Little Endian CPU(s): 8 On-line CPU(s) list: 0-7 Thread(s) per core: 2 Core(s) per socket: 4 Socket(s): 1 NUMA node(s): 1 Vendor ID: AuthenticAMD CPU family: 21 Model: 2 Model name: AMD FX(tm)-8350 Eight-Core Processor Stepping: 0 CPU MHz: 3584.018 CPU max MHz: 4000.0000 CPU min MHz: 1400.0000 BogoMIPS: 8027.22 Virtualization: AMD-V L1d cache: 16K L1i cache: 64K L2 cache: 2048K L3 cache: 8192K NUMA node0 CPU(s): 0-7 Flags: fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush mmx fxsr sse sse2 ht syscall nx mmxext fxsr_opt pdpe1gb rdtscp lm constant_tsc rep_good nopl nonstop_tsc cpuid extd_apicid aperfmperf pni pclmulqdq monitor ssse3 fma cx16 sse4_1 sse4_2 popcnt aes xsave avx f16c lahf_lm cmp_legacy svm extapic cr8_legacy abm sse4a misalignsse 3dnowprefetch osvw ibs xop skinit wdt lwp fma4 tce nodeid_msr tbm topoext perfctr_core perfctr_nb cpb hw_pstate vmmcall bmi1 arat npt lbrv svm_lock nrip_save tsc_scale vmcb_clean flushbyasid decodeassists pausefilter pfthreshold
So this is model-2 bulldozer AMD CPU.
GCC agrees:
$ echo | gcc -E - -march=native -### <...> /usr/lib/gcc/x86_64-linux-gnu/7/cc1 -E -quiet -imultiarch x86_64-linux-gnu - "-march=bdver2" -mmmx -mno-3dnow -msse -msse2 -msse3 -mssse3 -msse4a -mcx16 -msahf -mno-movbe -maes -mno-sha -mpclmul -mpopcnt -mabm -mlwp -mfma -mfma4 -mxop -mbmi -mno-sgx -mno-bmi2 -mtbm -mavx -mno-avx2 -msse4.2 -msse4.1 -mlzcnt -mno-rtm -mno-hle -mno-rdrnd -mf16c -mno-fsgsbase -mno-rdseed -mprfchw -mno-adx -mfxsr -mxsave -mno-xsaveopt -mno-avx512f -mno-avx512er -mno-avx512cd -mno-avx512pf -mno-prefetchwt1 -mno-clflushopt -mno-xsavec -mno-xsaves -mno-avx512dq -mno-avx512bw -mno-avx512vl -mno-avx512ifma -mno-avx512vbmi -mno-avx5124fmaps -mno-avx5124vnniw -mno-clwb -mno-mwaitx -mno-clzero -mno-pku -mno-rdpid --param "l1-cache-size=16" --param "l1-cache-line-size=64" --param "l2-cache-size=2048" "-mtune=bdver2" <...>
But clang does not: (look for bdver1)
$ echo | clang -E - -march=native -### clang version 7.0.0- (trunk) Target: x86_64-pc-linux-gnu Thread model: posix InstalledDir: /usr/local/bin "/usr/lib/llvm-7/bin/clang" "-cc1" "-triple" "x86_64-pc-linux-gnu" "-E" "-disable-free" "-disable-llvm-verifier" "-discard-value-names" "-main-file-name" "-" "-mrelocation-model" "static" "-mthread-model" "posix" "-mdisable-fp-elim" "-fmath-errno" "-masm-verbose" "-mconstructor-aliases" "-munwind-tables" "-fuse-init-array" "-target-cpu" "bdver1" "-target-feature" "+sse2" "-target-feature" "+cx16" "-target-feature" "+sahf" "-target-feature" "+tbm" "-target-feature" "-avx512ifma" "-target-feature" "-sha" "-target-feature" "-gfni" "-target-feature" "+fma4" "-target-feature" "-vpclmulqdq" "-target-feature" "+prfchw" "-target-feature" "-bmi2" "-target-feature" "-cldemote" "-target-feature" "-fsgsbase" "-target-feature" "-xsavec" "-target-feature" "+popcnt" "-target-feature" "+aes" "-target-feature" "-avx512bitalg" "-target-feature" "-xsaves" "-target-feature" "-avx512er" "-target-feature" "-avx512vnni" "-target-feature" "-avx512vpopcntdq" "-target-feature" "-clwb" "-target-feature" "-avx512f" "-target-feature" "-clzero" "-target-feature" "-pku" "-target-feature" "+mmx" "-target-feature" "+lwp" "-target-feature" "-rdpid" "-target-feature" "+xop" "-target-feature" "-rdseed" "-target-feature" "-waitpkg" "-target-feature" "-ibt" "-target-feature" "+sse4a" "-target-feature" "-avx512bw" "-target-feature" "-clflushopt" "-target-feature" "+xsave" "-target-feature" "-avx512vbmi2" "-target-feature" "-avx512vl" "-target-feature" "-avx512cd" "-target-feature" "+avx" "-target-feature" "-vaes" "-target-feature" "-rtm" "-target-feature" "+fma" "-target-feature" "+bmi" "-target-feature" "-rdrnd" "-target-feature" "-mwaitx" "-target-feature" "+sse4.1" "-target-feature" "+sse4.2" "-target-feature" "-avx2" "-target-feature" "-wbnoinvd" "-target-feature" "+sse" "-target-feature" "+lzcnt" "-target-feature" "+pclmul" "-target-feature" "-prefetchwt1" "-target-feature" "+f16c" "-target-feature" "+ssse3" "-target-feature" "-sgx" "-target-feature" "-shstk" "-target-feature" "+cmov" "-target-feature" "-avx512vbmi" "-target-feature" "-movbe" "-target-feature" "-xsaveopt" "-target-feature" "-avx512dq" "-target-feature" "-adx" "-target-feature" "-avx512pf" "-target-feature" "+sse3" "-dwarf-column-info" "-debugger-tuning=gdb" "-resource-dir" "/usr/lib/llvm-7/lib/clang/7.0.0" "-internal-isystem" "/usr/local/include" "-internal-isystem" "/usr/lib/llvm-7/lib/clang/7.0.0/include" "-internal-externc-isystem" "/usr/include/x86_64-linux-gnu" "-internal-externc-isystem" "/include" "-internal-externc-isystem" "/usr/include" "-fdebug-compilation-dir" "/build/llvm-build-Clang-release" "-ferror-limit" "19" "-fmessage-length" "271" "-fobjc-runtime=gcc" "-fdiagnostics-show-option" "-fcolor-diagnostics" "-o" "-" "-x" "c" "-"
So clang, unlike gcc, considers this to be bdver1.
After some digging, i've come across getAMDProcessorTypeAndSubtype() in Host.cpp.
I have added the following debug printf after the call to that function in sys::getHostCPUName():
errs() << "Family " << Family << " Model " << Model << " Type " << Type "\n";
Which produced:
Family 21 Model 2 Type 5
Which matches the lscpu output.
As it was pointed in the review by @craig.topper:
Though It does not help that the code can't be tested at the moment.
With this logical change, the bdver2 is properly detected.
$ echo | /build/llvm-build-Clang-release/bin/clang -E - -march=native -### clang version 7.0.0 (trunk 331249) (llvm/trunk 331256) Target: x86_64-unknown-linux-gnu Thread model: posix InstalledDir: /build/llvm-build-Clang-release/bin "/build/llvm-build-Clang-release/bin/clang-7" "-cc1" "-triple" "x86_64-unknown-linux-gnu" "-E" "-disable-free" "-main-file-name" "-" "-mrelocation-model" "static" "-mthread-model" "posix" "-mdisable-fp-elim" "-fmath-errno" "-masm-verbose" "-mconstructor-aliases" "-munwind-tables" "-fuse-init-array" "-target-cpu" "bdver2" "-target-feature" "+sse2" "-target-feature" "+cx16" "-target-feature" "+sahf" "-target-feature" "+tbm" "-target-feature" "-avx512ifma" "-target-feature" "-sha" "-target-feature" "-gfni" "-target-feature" "+fma4" "-target-feature" "-vpclmulqdq" "-target-feature" "+prfchw" "-target-feature" "-bmi2" "-target-feature" "-cldemote" "-target-feature" "-fsgsbase" "-target-feature" "-xsavec" "-target-feature" "+popcnt" "-target-feature" "+aes" "-target-feature" "-avx512bitalg" "-target-feature" "-movdiri" "-target-feature" "-xsaves" "-target-feature" "-avx512er" "-target-feature" "-avx512vnni" "-target-feature" "-avx512vpopcntdq" "-target-feature" "-clwb" "-target-feature" "-avx512f" "-target-feature" "-clzero" "-target-feature" "-pku" "-target-feature" "+mmx" "-target-feature" "+lwp" "-target-feature" "-rdpid" "-target-feature" "+xop" "-target-feature" "-rdseed" "-target-feature" "-waitpkg" "-target-feature" "-movdir64b" "-target-feature" "-ibt" "-target-feature" "+sse4a" "-target-feature" "-avx512bw" "-target-feature" "-clflushopt" "-target-feature" "+xsave" "-target-feature" "-avx512vbmi2" "-target-feature" "-avx512vl" "-target-feature" "-avx512cd" "-target-feature" "+avx" "-target-feature" "-vaes" "-target-feature" "-rtm" "-target-feature" "+fma" "-target-feature" "+bmi" "-target-feature" "-rdrnd" "-target-feature" "-mwaitx" "-target-feature" "+sse4.1" "-target-feature" "+sse4.2" "-target-feature" "-avx2" "-target-feature" "-wbnoinvd" "-target-feature" "+sse" "-target-feature" "+lzcnt" "-target-feature" "+pclmul" "-target-feature" "-prefetchwt1" "-target-feature" "+f16c" "-target-feature" "+ssse3" "-target-feature" "-sgx" "-target-feature" "-shstk" "-target-feature" "+cmov" "-target-feature" "-avx512vbmi" "-target-feature" "-movbe" "-target-feature" "-xsaveopt" "-target-feature" "-avx512dq" "-target-feature" "-adx" "-target-feature" "-avx512pf" "-target-feature" "+sse3" "-dwarf-column-info" "-debugger-tuning=gdb" "-resource-dir" "/build/llvm-build-Clang-release/lib/clang/7.0.0" "-internal-isystem" "/usr/local/include" "-internal-isystem" "/build/llvm-build-Clang-release/lib/clang/7.0.0/include" "-internal-externc-isystem" "/usr/include/x86_64-linux-gnu" "-internal-externc-isystem" "/include" "-internal-externc-isystem" "/usr/include" "-fdebug-compilation-dir" "/build/llvm-build-Clang-release" "-ferror-limit" "19" "-fmessage-length" "271" "-fobjc-runtime=gcc" "-fdiagnostics-show-option" "-fcolor-diagnostics" "-o" "-" "-x" "c" "-"
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