We currently emit up to 15-byte NOPs on all targets (apart from Silvermont), which stalls performance on some targets with decoders that struggle with 2 or 3 more '66' prefixes.
This patch flags recent AMD targets (btver1/znver1) to still emit 15-byte NOPs and bdver* targets to emit 11-byte NOPs. All other targets now emit 10-byte NOPs apart from SilverMont CPUs which still emit 7-byte NOPS.
Differential Revision: https://reviews.llvm.org/D42616
llvm-svn: 323693
Empty string should be equivalent to "generic" which doesn't allow NOPL. Force tests to use specificy 'pentiumpro' to guarantee NOPL.
Fixes PR35686
llvm-svn: 321026
not all lakemont MCU support long nop.
we can't assume we can generate long nop by default for MCU.
Differential Revision: https://reviews.llvm.org/D26895
llvm-svn: 288363
Restrict the max length of long nops for Lakemont to 7. Experiments on MCU
benchmarks (Dhrystone, Coremark) show that this is the most optimal length.
Differential Revision: http://reviews.llvm.org/D18897
llvm-svn: 265924
Silvermont can only decode one instruction per cycle if the instruction exceeds 8 bytes.
Also in Silvermont instructions with more than 3 prefixes will cause 3 cycle penalty.
Maximum nop length is limited to 7 bytes when used for padding on Silvermont.
For other x86 processors max nop length remains unchanged 15 bytes.
Differential Revision: http://reviews.llvm.org/D4374
llvm-svn: 212321
Simon Pilgrim