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[HotColdSplit] Add options for splitting cold functions in separate section

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Add support for (if enabled) splitting cold functions into a separate section
in order to further boost locality of hot code.

Authored by: rjf (Ruijie Fang)
Reviewed by: hiraditya,rcorcs,vsk

Differential Revision: https://reviews.llvm.org/D85331
This commit is contained in:
Aditya Kumar 2020-08-09 08:45:36 -07:00
parent 1bcc62d24e
commit b003049fb3
3 changed files with 97 additions and 2 deletions
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20
lib/Transforms/IPO/HotColdSplitting.cpp
View File

@ -69,6 +69,7 @@
#include "llvm/Transforms/Utils/ValueMapper.h"
#include <algorithm>
#include <cassert>
#include <string>
#define DEBUG_TYPE "hotcoldsplit"
@ -85,6 +86,17 @@ static cl::opt<int>
cl::desc("Base penalty for splitting cold code (as a "
"multiple of TCC_Basic)"));
static cl::opt<bool> EnableColdSection(
"enable-cold-section", cl::init(false), cl::Hidden,
cl::desc("Enable placement of extracted cold functions"
" into a separate section after hot-cold splitting."));
static cl::opt<std::string>
ColdSectionName("hotcoldsplit-cold-section-name", cl::init("__llvm_cold"),
cl::Hidden,
cl::desc("Name for the section containing cold functions "
"extracted by hot-cold splitting."));
namespace {
// Same as blockEndsInUnreachable in CodeGen/BranchFolding.cpp. Do not modify
// this function unless you modify the MBB version as well.
@ -339,8 +351,12 @@ Function *HotColdSplitting::extractColdRegion(
}
CI->setIsNoInline();
if (OrigF->hasSection())
OutF->setSection(OrigF->getSection());
if (EnableColdSection)
OutF->setSection(ColdSectionName);
else {
if (OrigF->hasSection())
OutF->setSection(OrigF->getSection());
}
markFunctionCold(*OutF, BFI != nullptr);

40
test/Transforms/HotColdSplit/section-splitting-custom.ll Normal file
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@ -0,0 +1,40 @@
; RUN: opt -hotcoldsplit -hotcoldsplit-threshold=-1 -pass-remarks=hotcoldsplit -enable-cold-section=true -hotcoldsplit-cold-section-name="__cold_custom" -S < %s 2>&1 | FileCheck %s
; RUN: opt -passes=hotcoldsplit -hotcoldsplit-threshold=-1 -pass-remarks=hotcoldsplit -enable-cold-section=true -hotcoldsplit-cold-section-name="__cold_custom" -S < %s 2>&1 | FileCheck %s
; This test case is copied over from split-cold-2.ll, modified
; to test the `-enable-cold-section` and `-hotcoldsplit-cold-section-name`
; parameters in opt.
; Make sure this compiles. This test used to fail with an invalid phi node: the
; two predecessors were outlined and the SSA representation was invalid.
; CHECK: remark: <unknown>:0:0: fun split cold code into fun.cold.1
; CHECK-LABEL: @fun
; CHECK: codeRepl:
; CHECK-NEXT: call void @fun.cold.1
; CHECK: define {{.*}}@fun.cold.1{{.*}} [[cold_attr:#[0-9]+]] section "__cold_custom"
; CHECK: attributes [[cold_attr]] = { {{.*}}noreturn
define void @fun() {
entry:
br i1 undef, label %if.then, label %if.else
if.then:
ret void
if.else:
br label %if.then4
if.then4:
br i1 undef, label %if.then5, label %if.end
if.then5:
br label %cleanup
if.end:
br label %cleanup
cleanup:
%cleanup.dest.slot.0 = phi i32 [ 1, %if.then5 ], [ 0, %if.end ]
unreachable
}

39
test/Transforms/HotColdSplit/section-splitting-default.ll Normal file
View File

@ -0,0 +1,39 @@
; RUN: opt -hotcoldsplit -hotcoldsplit-threshold=-1 -pass-remarks=hotcoldsplit -enable-cold-section=true -S < %s 2>&1 | FileCheck %s
; RUN: opt -passes=hotcoldsplit -hotcoldsplit-threshold=-1 -pass-remarks=hotcoldsplit -enable-cold-section=true -S < %s 2>&1 | FileCheck %s
; This test case is copied over from split-cold-2.ll, modified
; to test the `-enable-cold-section` parameter in opt.
; Make sure this compiles. This test used to fail with an invalid phi node: the
; two predecessors were outlined and the SSA representation was invalid.
; CHECK: remark: <unknown>:0:0: fun split cold code into fun.cold.1
; CHECK-LABEL: @fun
; CHECK: codeRepl:
; CHECK-NEXT: call void @fun.cold.1
; CHECK: define {{.*}}@fun.cold.1{{.*}} [[cold_attr:#[0-9]+]] section "__llvm_cold"
; CHECK: attributes [[cold_attr]] = { {{.*}}noreturn
define void @fun() {
entry:
br i1 undef, label %if.then, label %if.else
if.then:
ret void
if.else:
br label %if.then4
if.then4:
br i1 undef, label %if.then5, label %if.end
if.then5:
br label %cleanup
if.end:
br label %cleanup
cleanup:
%cleanup.dest.slot.0 = phi i32 [ 1, %if.then5 ], [ 0, %if.end ]
unreachable
}