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[X86] Emit 11-byte or 15-byte NOPs on recent AMD targets, else default to 10-byte NOPs (PR22965)

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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
This commit is contained in:
Simon Pilgrim 2018-01-29 21:24:31 +00:00
parent 407184bd30
commit 7d8c42b67e
10 changed files with 90 additions and 33 deletions
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14
lib/Target/X86/MCTargetDesc/X86AsmBackend.cpp
View File

@ -344,10 +344,18 @@ bool X86AsmBackend::writeNopData(uint64_t Count, MCObjectWriter *OW) const {
return true;
}
uint64_t MaxNopLength = STI.getFeatureBits()[X86::ProcIntelSLM] ? 7 : 15;
// 15-bytes is the longest single NOP instruction, but 10-bytes is
// commonly the longest that can be efficiently decoded.
uint64_t MaxNopLength = 10;
if (STI.getFeatureBits()[X86::ProcIntelSLM])
MaxNopLength = 7;
else if (STI.getFeatureBits()[X86::FeatureFast15ByteNOP])
MaxNopLength = 15;
else if (STI.getFeatureBits()[X86::FeatureFast11ByteNOP])
MaxNopLength = 11;
// 15 is the longest single nop instruction. Emit as many 15-byte nops as
// needed, then emit a nop of the remaining length.
// Emit as many MaxNopLength NOPs as needed, then emit a NOP of the remaining
// length.
do {
const uint8_t ThisNopLength = (uint8_t) std::min(Count, MaxNopLength);
const uint8_t Prefixes = ThisNopLength <= 10 ? 0 : ThisNopLength - 10;

21
lib/Target/X86/X86.td
View File

@ -305,8 +305,16 @@ def FeatureFastLZCNT
: SubtargetFeature<
"fast-lzcnt", "HasFastLZCNT", "true",
"LZCNT instructions are as fast as most simple integer ops">;
// If the target can efficiently decode NOPs upto 11-bytes in length.
def FeatureFast11ByteNOP
: SubtargetFeature<
"fast-11bytenop", "HasFast11ByteNOP", "true",
"Target can quickly decode up to 11 byte NOPs">;
// If the target can efficiently decode NOPs upto 15-bytes in length.
def FeatureFast15ByteNOP
: SubtargetFeature<
"fast-15bytenop", "HasFast15ByteNOP", "true",
"Target can quickly decode up to 15 byte NOPs">;
// Sandy Bridge and newer processors can use SHLD with the same source on both
// inputs to implement rotate to avoid the partial flag update of the normal
// rotate instructions.
@ -849,7 +857,8 @@ def : Proc<"btver1", [
FeatureLZCNT,
FeaturePOPCNT,
FeatureSlowSHLD,
FeatureLAHFSAHF
FeatureLAHFSAHF,
FeatureFast15ByteNOP
]>;
// Jaguar
@ -874,6 +883,7 @@ def : ProcessorModel<"btver2", BtVer2Model, [
FeatureXSAVEOPT,
FeatureSlowSHLD,
FeatureLAHFSAHF,
FeatureFast15ByteNOP,
FeatureFastPartialYMMorZMMWrite
]>;
@ -897,6 +907,7 @@ def : Proc<"bdver1", [
FeatureLWP,
FeatureSlowSHLD,
FeatureLAHFSAHF,
FeatureFast11ByteNOP,
FeatureMacroFusion
]>;
// Piledriver
@ -923,6 +934,7 @@ def : Proc<"bdver2", [
FeatureFMA,
FeatureSlowSHLD,
FeatureLAHFSAHF,
FeatureFast11ByteNOP,
FeatureMacroFusion
]>;
@ -952,6 +964,7 @@ def : Proc<"bdver3", [
FeatureSlowSHLD,
FeatureFSGSBase,
FeatureLAHFSAHF,
FeatureFast11ByteNOP,
FeatureMacroFusion
]>;
@ -981,6 +994,7 @@ def : Proc<"bdver4", [
FeatureSlowSHLD,
FeatureFSGSBase,
FeatureLAHFSAHF,
FeatureFast11ByteNOP,
FeatureMWAITX,
FeatureMacroFusion
]>;
@ -1003,6 +1017,7 @@ def: ProcessorModel<"znver1", Znver1Model, [
FeatureFastLZCNT,
FeatureLAHFSAHF,
FeatureLZCNT,
FeatureFast15ByteNOP,
FeatureMacroFusion,
FeatureMMX,
FeatureMOVBE,

2
lib/Target/X86/X86Subtarget.cpp
View File

@ -335,6 +335,8 @@ void X86Subtarget::initializeEnvironment() {
HasLZCNTFalseDeps = false;
HasFastVariableShuffle = false;
HasFastPartialYMMorZMMWrite = false;
HasFast11ByteNOP = false;
HasFast15ByteNOP = false;
HasFastGather = false;
HasFastScalarFSQRT = false;
HasFastVectorFSQRT = false;

8
lib/Target/X86/X86Subtarget.h
View File

@ -246,6 +246,14 @@ protected:
/// of a YMM or ZMM register without clearing the upper part.
bool HasFastPartialYMMorZMMWrite;
/// True if there is no performance penalty for writing NOPs with up to
/// 11 bytes.
bool HasFast11ByteNOP;
/// True if there is no performance penalty for writing NOPs with up to
/// 15 bytes.
bool HasFast15ByteNOP;
/// True if gather is reasonably fast. This is true for Skylake client and
/// all AVX-512 CPUs.
bool HasFastGather;

12
test/MC/MachO/x86_32-optimal_nop.s
View File

@ -202,15 +202,15 @@ f0:
// CHECK: 0090: C3000000 00000000 00000000 00000000 |................|
// CHECK: 00A0: C3C3C3C3 C3C3C366 0F1F8400 00000000 |.......f........|
// CHECK: 00B0: C3000000 00000000 00000000 00000000 |................|
// CHECK: 00C0: C3C3C3C3 C366662E 0F1F8400 00000000 |.....ff.........|
// CHECK: 00C0: C3C3C3C3 C3662E0F 1F840000 00000090 |.....f..........|
// CHECK: 00D0: C3000000 00000000 00000000 00000000 |................|
// CHECK: 00E0: C3C3C3C3 6666662E 0F1F8400 00000000 |....fff.........|
// CHECK: 00E0: C3C3C3C3 662E0F1F 84000000 00006690 |....f.........f.|
// CHECK: 00F0: C3000000 00000000 00000000 00000000 |................|
// CHECK: 0100: C3C3C366 6666662E 0F1F8400 00000000 |...ffff.........|
// CHECK: 0100: C3C3C366 2E0F1F84 00000000 000F1F00 |...f............|
// CHECK: 0110: C3000000 00000000 00000000 00000000 |................|
// CHECK: 0120: C3C36666 6666662E 0F1F8400 00000000 |..fffff.........|
// CHECK: 0120: C3C3662E 0F1F8400 00000000 0F1F4000 |..f...........@.|
// CHECK: 0130: C3000000 00000000 00000000 00000000 |................|
// CHECK: 0140: C3666666 6666662E 0F1F8400 00000000 |.ffffff.........|
// CHECK: 0140: C3662E0F 1F840000 0000000F 1F440000 |.f...........D..|
// CHECK: 0150: C3 |.|
// CHECK: )
// CHECK: }
@ -255,7 +255,7 @@ f0:
// CHECK: }
// CHECK: Segment {
// CHECK: Cmd: LC_SEGMENT
// CHECK: Name:
// CHECK: Name:
// CHECK: Size: 192
// CHECK: vmaddr: 0x0
// CHECK: vmsize: 0x174

10
test/MC/X86/AlignedBundling/long-nop-pad.s
View File

@ -13,17 +13,19 @@ foo:
.bundle_lock align_to_end
callq bar
.bundle_unlock
# To align this group to a bundle end, we need a 15-byte NOP and a 12-byte NOP.
# To align this group to a bundle end, we need a two 10-byte NOPs and a 7-byte NOP.
# CHECK: 0: nop
# CHECK-NEXT: f: nop
# CHECK-NEXT: a: nop
# CHECK-NEXT: 14: nop
# CHECK: 1b: callq
# This push instruction is 1 byte long
.bundle_lock align_to_end
push %rax
.bundle_unlock
# To align this group to a bundle end, we need two 15-byte NOPs, and a 1-byte.
# To align this group to a bundle end, we need three 10-byte NOPs, and a 1-byte.
# CHECK: 20: nop
# CHECK-NEXT: 2f: nop
# CHECK-NEXT: 2a: nop
# CHECK-NEXT: 34: nop
# CHECK-NEXT: 3e: nop
# CHECK-NEXT: 3f: pushq

4
test/MC/X86/AlignedBundling/misaligned-bundle-group.s
View File

@ -13,9 +13,9 @@ foo:
.bundle_lock align_to_end
# CHECK: 1: nopw %cs:(%eax,%eax)
# CHECK: 10: nopw %cs:(%eax,%eax)
# CHECK-RELAX: 1f: nop
# CHECK-RELAX: 1a: nop
# CHECK-RELAX: 20: nopw %cs:(%eax,%eax)
# CHECK-RELAX: 2f: nopw %cs:(%eax,%eax)
# CHECK-RELAX: 2a: nopw %cs:(%eax,%eax)
# CHECK-OPT: 1b: calll -4
# CHECK-RELAX: 3b: calll -4
calll bar # 5 bytes

2
test/MC/X86/AlignedBundling/misaligned-bundle.s
View File

@ -12,7 +12,7 @@ foo:
.align 16
# CHECK: 1: nopw %cs:(%eax,%eax)
# CHECK-RELAX: 10: nopw %cs:(%eax,%eax)
# CHECK-RELAX: 1f: nop
# CHECK-RELAX: 1a: nop
# CHECK-OPT: 10: movl $1, (%esp)
# CHECK-RELAX: 20: movl $1, (%esp)
movl $0x1, (%esp) # 7 bytes

3
test/MC/X86/AlignedBundling/pad-bundle-groups.s
View File

@ -38,9 +38,10 @@ foo:
callq bar
callq bar
.bundle_unlock
# And here we'll need a 11-byte NOP
# And here we'll need a 10-byte NOP + 1-byte NOP
# CHECK: 30: callq
# CHECK: 35: nop
# CHECK: 3f: nop
# CHECK-NEXT: 40: callq
# CHECK-NEXT: 45: callq

47
test/MC/X86/x86_long_nop.s
View File

@ -1,30 +1,51 @@
# RUN: llvm-mc -filetype=obj -arch=x86 -triple=x86_64-pc-linux-gnu -mcpu=pentiumpro %s | llvm-objdump -d -no-show-raw-insn - | FileCheck %s
# RUN: llvm-mc -filetype=obj -arch=x86 -triple=i686-pc-linux-gnu %s -mcpu=pentiumpro | llvm-objdump -d -no-show-raw-insn - | FileCheck %s
# RUN: llvm-mc -filetype=obj -arch=x86 -triple=x86_64-apple-darwin10.0 -mcpu=pentiumpro %s | llvm-objdump -d -no-show-raw-insn - | FileCheck %s
# RUN: llvm-mc -filetype=obj -arch=x86 -triple=i686-apple-darwin8 -mcpu=pentiumpro %s | llvm-objdump -d -no-show-raw-insn - | FileCheck %s
# RUN: llvm-mc -filetype=obj -arch=x86 -triple=x86_64-pc-linux-gnu -mcpu=pentiumpro %s | llvm-objdump -d -no-show-raw-insn - | FileCheck %s --check-prefix=LNOP10
# RUN: llvm-mc -filetype=obj -arch=x86 -triple=i686-pc-linux-gnu %s -mcpu=pentiumpro | llvm-objdump -d -no-show-raw-insn - | FileCheck %s --check-prefix=LNOP10
# RUN: llvm-mc -filetype=obj -arch=x86 -triple=x86_64-apple-darwin10.0 -mcpu=pentiumpro %s | llvm-objdump -d -no-show-raw-insn - | FileCheck %s --check-prefix=LNOP10
# RUN: llvm-mc -filetype=obj -arch=x86 -triple=i686-apple-darwin8 -mcpu=pentiumpro %s | llvm-objdump -d -no-show-raw-insn - | FileCheck %s --check-prefix=LNOP10
# 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=silvermont %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=NOP1 %s
# RUN: llvm-mc -filetype=obj -arch=x86 -triple=x86_64-pc-linux-gnu -mcpu=bdver1 %s | llvm-objdump -d -no-show-raw-insn - | FileCheck %s --check-prefix=LNOP11
# RUN: llvm-mc -filetype=obj -arch=x86 -triple=i686-pc-linux-gnu %s -mcpu=bdver1 | llvm-objdump -d -no-show-raw-insn - | FileCheck %s --check-prefix=LNOP11
# RUN: llvm-mc -filetype=obj -arch=x86 -triple=x86_64-pc-linux-gnu -mcpu=btver1 %s | llvm-objdump -d -no-show-raw-insn - | FileCheck %s --check-prefix=LNOP15
# RUN: llvm-mc -filetype=obj -arch=x86 -triple=i686-pc-linux-gnu %s -mcpu=btver1 | llvm-objdump -d -no-show-raw-insn - | FileCheck %s --check-prefix=LNOP15
# RUN: llvm-mc -filetype=obj -arch=x86 -triple=x86_64-pc-linux-gnu -mcpu=btver2 %s | llvm-objdump -d -no-show-raw-insn - | FileCheck %s --check-prefix=LNOP15
# RUN: llvm-mc -filetype=obj -arch=x86 -triple=i686-pc-linux-gnu %s -mcpu=btver2 | llvm-objdump -d -no-show-raw-insn - | FileCheck %s --check-prefix=LNOP15
# RUN: llvm-mc -filetype=obj -arch=x86 -triple=x86_64-pc-linux-gnu -mcpu=znver1 %s | llvm-objdump -d -no-show-raw-insn - | FileCheck %s --check-prefix=LNOP15
# RUN: llvm-mc -filetype=obj -arch=x86 -triple=i686-pc-linux-gnu %s -mcpu=znver1 | llvm-objdump -d -no-show-raw-insn - | FileCheck %s --check-prefix=LNOP15
# Ensure alignment directives also emit sequences of 15-byte NOPs on processors
# Ensure alignment directives also emit sequences of 10, 11 and 15-byte NOPs on processors
# capable of using long NOPs.
inc %eax
.p2align 5
inc %eax
# CHECK: 0: inc
# CHECK-NEXT: 1: nop
# CHECK-NEXT: 10: nop
# CHECK-NEXT: 1f: nop
# CHECK-NEXT: 20: inc
# LNOP15: 0: inc
# LNOP15-NEXT: 1: nop
# LNOP15-NEXT: 10: nop
# LNOP15-NEXT: 1f: nop
# LNOP15-NEXT: 20: inc
# LNOP11: 0: inc
# LNOP11-NEXT: 1: nop
# LNOP11-NEXT: c: nop
# LNOP11-NEXT: 17: nop
# LNOP11-NEXT: 20: inc
# LNOP10: 0: inc
# LNOP10-NEXT: 1: nop
# LNOP10-NEXT: b: nop
# LNOP10-NEXT: 15: nop
# LNOP10-NEXT: 1f: nop
# LNOP10-NEXT: 20: inc
# On Silvermont 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
# LNOP7-NEXT: 16: nop
# LNOP7-NEXT: 1d: nop
# LNOP7-NEXT: 20: inc
# On Lakemont we emit only 1 byte NOPs since longer NOPs are not supported/legal
# NOP1: 0: inc