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[X86] Restrict max long nop length for Lakemont.

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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
This commit is contained in:
Andrey Turetskiy 2016-04-11 10:07:36 +00:00
parent 979adb799a
commit 79cd7e75f9
2 changed files with 13 additions and 10 deletions
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3
lib/Target/X86/MCTargetDesc/X86AsmBackend.cpp
View File

@ -72,7 +72,8 @@ class X86AsmBackend : public MCAsmBackend {
const uint64_t MaxNopLength;
public:
X86AsmBackend(const Target &T, StringRef CPU)
: MCAsmBackend(), CPU(CPU), MaxNopLength(CPU == "slm" ? 7 : 15) {
: MCAsmBackend(), CPU(CPU),
MaxNopLength((CPU == "slm" || CPU == "lakemont") ? 7 : 15) {
HasNopl = CPU != "generic" && CPU != "i386" && CPU != "i486" &&
CPU != "i586" && CPU != "pentium" && CPU != "pentium-mmx" &&
CPU != "i686" && CPU != "k6" && CPU != "k6-2" && CPU != "k6-3" &&

20
test/MC/X86/x86_long_nop.s
View File

@ -2,7 +2,8 @@
# RUN: llvm-mc -filetype=obj -arch=x86 -triple=i686-pc-linux-gnu %s | llvm-objdump -d -no-show-raw-insn - | FileCheck %s
# RUN: llvm-mc -filetype=obj -arch=x86 -triple=x86_64-apple-darwin10.0 %s | llvm-objdump -d -no-show-raw-insn - | FileCheck %s
# RUN: llvm-mc -filetype=obj -arch=x86 -triple=i686-apple-darwin8 %s | llvm-objdump -d -no-show-raw-insn - | FileCheck %s
# RUN: llvm-mc -filetype=obj -arch=x86 -triple=i686-pc-linux-gnu -mcpu=slm %s | llvm-objdump -d -no-show-raw-insn - | FileCheck --check-prefix=SLM %s
# RUN: llvm-mc -filetype=obj -arch=x86 -triple=i686-pc-linux-gnu -mcpu=slm %s | llvm-objdump -d -no-show-raw-insn - | FileCheck --check-prefix=LNOP7 %s
# RUN: llvm-mc -filetype=obj -arch=x86 -triple=i686-pc-linux-gnu -mcpu=lakemont %s | llvm-objdump -d -no-show-raw-insn - | FileCheck --check-prefix=LNOP7 %s
# Ensure alignment directives also emit sequences of 15-byte NOPs on processors
# capable of using long NOPs.
@ -15,11 +16,12 @@ inc %eax
# CHECK-NEXT: 1f: nop
# CHECK-NEXT: 20: inc
# On Silvermont we emit only 7 byte NOPs since longer NOPs are not profitable
# SLM: 0: inc
# SLM-NEXT: 1: nop
# SLM-NEXT: 8: nop
# SLM-NEXT: f: nop
# SLM-NEXT: 16: nop
# SLM-NEXT: 1d: nop
# SLM-NEXT: 20: inc
# On Silvermont and Lakemont we emit only 7 byte NOPs since longer NOPs
# are not profitable.
# LNOP7: 0: inc
# LNOP7-NEXT: 1: nop
# LNOP7-NEXT: 8: nop
# LNOP7-NEXT: f: nop
# LNOP7-NEXT: 16: nop
# LNOP7-NEXT: 1d: nop
# LNOP7-NEXT: 20: inc