[As of 22-SEP-2015; Tested with version qemu-2.3.0-6.fc22.x86_64]

$ qemu-system-x86_64 -cpu \?
x86           qemu64  QEMU Virtual CPU version 2.3.0                  
x86           phenom  AMD Phenom(tm) 9550 Quad-Core Processor         
x86         core2duo  Intel(R) Core(TM)2 Duo CPU     T7700  @ 2.40GHz 
x86            kvm64  Common KVM processor                            
x86           qemu32  QEMU Virtual CPU version 2.3.0                  
x86            kvm32  Common 32-bit KVM processor                     
x86          coreduo  Genuine Intel(R) CPU           T2600  @ 2.16GHz 
x86              486                                                  
x86          pentium                                                  
x86         pentium2                                                  
x86         pentium3                                                  
x86           athlon  QEMU Virtual CPU version 2.3.0                  
x86             n270  Intel(R) Atom(TM) CPU N270   @ 1.60GHz          
x86           Conroe  Intel Celeron_4x0 (Conroe/Merom Class Core 2)   
x86           Penryn  Intel Core 2 Duo P9xxx (Penryn Class Core 2)    
x86          Nehalem  Intel Core i7 9xx (Nehalem Class Core i7)       
x86         Westmere  Westmere E56xx/L56xx/X56xx (Nehalem-C)          
x86      SandyBridge  Intel Xeon E312xx (Sandy Bridge)                
x86        IvyBridge  Intel Xeon E3-12xx v2 (Ivy Bridge)              
x86    Haswell-noTSX  Intel Core Processor (Haswell, no TSX)          
x86          Haswell  Intel Core Processor (Haswell)                  
x86  Broadwell-noTSX  Intel Core Processor (Broadwell, no TSX)        
x86        Broadwell  Intel Core Processor (Broadwell)                
x86       Opteron_G1  AMD Opteron 240 (Gen 1 Class Opteron)           
x86       Opteron_G2  AMD Opteron 22xx (Gen 2 Class Opteron)          
x86       Opteron_G3  AMD Opteron 23xx (Gen 3 Class Opteron)          
x86       Opteron_G4  AMD Opteron 62xx class CPU                      
x86       Opteron_G5  AMD Opteron 63xx class CPU                      
x86             host  KVM processor with all supported host features (only available in KVM mode)

Recognized CPUID flags:
  fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 pn clflush ds acpi mmx fxsr sse sse2 ss ht tm ia64 pbe
  pni|sse3 pclmulqdq|pclmuldq dtes64 monitor ds_cpl vmx smx est tm2 ssse3 cid fma cx16 xtpr pdcm pcid dca sse4.1|sse4_1 sse4.2|sse4_2 x2apic movbe popcnt tsc-deadline aes xsave osxsave avx f16c rdrand hypervisor
  fsgsbase tsc_adjust bmi1 hle avx2 smep bmi2 erms invpcid rtm mpx avx512f rdseed adx smap avx512pf avx512er avx512cd
  syscall nx|xd mmxext fxsr_opt|ffxsr pdpe1gb rdtscp lm|i64 3dnowext 3dnow
  lahf_lm cmp_legacy svm extapic cr8legacy abm sse4a misalignsse 3dnowprefetch osvw ibs xop skinit wdt lwp fma4 tce nodeid_msr tbm topoext perfctr_core perfctr_nb
  invtsc
  xstore xstore-en xcrypt xcrypt-en ace2 ace2-en phe phe-en pmm pmm-en
  kvmclock kvm_nopiodelay kvm_mmu kvmclock kvm_asyncpf kvm_steal_time kvm_pv_eoi kvm_pv_unhalt kvmclock-stable-bit
  npt lbrv svm_lock nrip_save tsc_scale vmcb_clean flushbyasid decodeassists pause_filter pfthreshold
  xsaveopt xsavec xgetbv1 xsaves