Avoid instructions that incur expensive length-changing prefix (LCP) stalls on some x86-64 implementations...
Avoid instructions that incur expensive length-changing prefix (LCP) stalls
on some x86-64 implementations, notably Core2 and Corei7. Specifically, a move of
a 16-bit constant into memory requires a length-changing prefix and can incur significant
penalties. Modified an old patch written by H.J to split such instructions
during peephole2.
2012-04-05 Teresa Johnson <tejohnson@google.com>
H.J. Lu <hongjiu.lu@intel.com>
* config/i386/i386.h (ix86_tune_indices): Add
X86_TUNE_LCP_STALL.
* config/i386/i386.md (move immediate to memory peephole2):
Add cases for HImode move when LCP stall avoidance is needed.
* config/i386/i386.c (initial_ix86_tune_features): Initialize
X86_TUNE_LCP_STALL entry.
Co-Authored-By: H.J. Lu <hongjiu.lu@intel.com>
From-SVN: r186176
