[lld] 109aac9 - [PDB] Enable parallel ghash type merging by default
Reid Kleckner via llvm-commits
llvm-commits at lists.llvm.org
Thu May 27 14:19:41 PDT 2021
Author: Reid Kleckner
Date: 2021-05-27T14:19:36-07:00
New Revision: 109aac92128ca958afe5141a59347c8a0733ea3e
URL: https://github.com/llvm/llvm-project/commit/109aac92128ca958afe5141a59347c8a0733ea3e
DIFF: https://github.com/llvm/llvm-project/commit/109aac92128ca958afe5141a59347c8a0733ea3e.diff
LOG: [PDB] Enable parallel ghash type merging by default
Ghashing is probably going to be faster in most cases, even without
precomputed ghashes in object files.
Here is my table of results linking clang.pdb:
-------------------------------
| threads | GHASH | NOGHASH |
-------------------------------
| j1 | 51.031s | 25.141s |
| j2 | 31.079s | 22.109s |
| j4 | 18.609s | 23.156s |
| j8 | 11.938s | 21.984s |
| j28 | 8.375s | 18.391s |
-------------------------------
This shows that ghashing is faster if at least four cores are available.
This may make the linker slower if most cores are busy in the middle of
a build, but in that case, the linker probably isn't on the critical
path of the build. Incremental build performance is arguably more
important than highly contended batch build link performance.
The -time output indicates that ghash computation is the dominant
factor:
Input File Reading: 924 ms ( 1.8%)
GC: 689 ms ( 1.3%)
ICF: 527 ms ( 1.0%)
Code Layout: 414 ms ( 0.8%)
Commit Output File: 24 ms ( 0.0%)
PDB Emission (Cumulative): 49938 ms ( 94.8%)
Add Objects: 46783 ms ( 88.8%)
Global Type Hashing: 38983 ms ( 74.0%)
GHash Type Merging: 5640 ms ( 10.7%)
Symbol Merging: 2154 ms ( 4.1%)
Publics Stream Layout: 188 ms ( 0.4%)
TPI Stream Layout: 18 ms ( 0.0%)
Commit to Disk: 2818 ms ( 5.4%)
--------------------------------------------------
Total Link Time: 52669 ms (100.0%)
We can speed that up with a faster content hash (not SHA1).
Differential Revision: https://reviews.llvm.org/D102888
Added:
Modified:
lld/COFF/Driver.cpp
lld/test/COFF/pdb-type-server-simple.test
Removed:
################################################################################
diff --git a/lld/COFF/Driver.cpp b/lld/COFF/Driver.cpp
index 03db71cc9082..97b3c9029e34 100644
--- a/lld/COFF/Driver.cpp
+++ b/lld/COFF/Driver.cpp
@@ -693,7 +693,16 @@ static std::string createResponseFile(const opt::InputArgList &args,
return std::string(data.str());
}
-enum class DebugKind { Unknown, None, Full, FastLink, GHash, Dwarf, Symtab };
+enum class DebugKind {
+ Unknown,
+ None,
+ Full,
+ FastLink,
+ GHash,
+ NoGHash,
+ Dwarf,
+ Symtab
+};
static DebugKind parseDebugKind(const opt::InputArgList &args) {
auto *a = args.getLastArg(OPT_debug, OPT_debug_opt);
@@ -703,14 +712,15 @@ static DebugKind parseDebugKind(const opt::InputArgList &args) {
return DebugKind::Full;
DebugKind debug = StringSwitch<DebugKind>(a->getValue())
- .CaseLower("none", DebugKind::None)
- .CaseLower("full", DebugKind::Full)
- .CaseLower("fastlink", DebugKind::FastLink)
- // LLD extensions
- .CaseLower("ghash", DebugKind::GHash)
- .CaseLower("dwarf", DebugKind::Dwarf)
- .CaseLower("symtab", DebugKind::Symtab)
- .Default(DebugKind::Unknown);
+ .CaseLower("none", DebugKind::None)
+ .CaseLower("full", DebugKind::Full)
+ .CaseLower("fastlink", DebugKind::FastLink)
+ // LLD extensions
+ .CaseLower("ghash", DebugKind::GHash)
+ .CaseLower("noghash", DebugKind::NoGHash)
+ .CaseLower("dwarf", DebugKind::Dwarf)
+ .CaseLower("symtab", DebugKind::Symtab)
+ .Default(DebugKind::Unknown);
if (debug == DebugKind::FastLink) {
warn("/debug:fastlink unsupported; using /debug:full");
@@ -1393,7 +1403,7 @@ void LinkerDriver::linkerMain(ArrayRef<const char *> argsArr) {
// Handle /debug
DebugKind debug = parseDebugKind(args);
if (debug == DebugKind::Full || debug == DebugKind::Dwarf ||
- debug == DebugKind::GHash) {
+ debug == DebugKind::GHash || debug == DebugKind::NoGHash) {
config->debug = true;
config->incremental = true;
}
@@ -1416,7 +1426,8 @@ void LinkerDriver::linkerMain(ArrayRef<const char *> argsArr) {
// Handle /pdb
bool shouldCreatePDB =
- (debug == DebugKind::Full || debug == DebugKind::GHash);
+ (debug == DebugKind::Full || debug == DebugKind::GHash ||
+ debug == DebugKind::NoGHash);
if (shouldCreatePDB) {
if (auto *arg = args.getLastArg(OPT_pdb))
config->pdbPath = arg->getValue();
@@ -1749,7 +1760,7 @@ void LinkerDriver::linkerMain(ArrayRef<const char *> argsArr) {
config->terminalServerAware =
!config->dll && args.hasFlag(OPT_tsaware, OPT_tsaware_no, true);
config->debugDwarf = debug == DebugKind::Dwarf;
- config->debugGHashes = debug == DebugKind::GHash;
+ config->debugGHashes = debug == DebugKind::GHash || debug == DebugKind::Full;
config->debugSymtab = debug == DebugKind::Symtab;
config->autoImport =
args.hasFlag(OPT_auto_import, OPT_auto_import_no, config->mingw);
diff --git a/lld/test/COFF/pdb-type-server-simple.test b/lld/test/COFF/pdb-type-server-simple.test
index 7c72d8fe8669..e9757d187e2f 100644
--- a/lld/test/COFF/pdb-type-server-simple.test
+++ b/lld/test/COFF/pdb-type-server-simple.test
@@ -20,7 +20,7 @@ RUN: rm -rf %t && mkdir -p %t && cd %t
RUN: yaml2obj %S/Inputs/pdb-type-server-simple-a.yaml -o a.obj
RUN: yaml2obj %S/Inputs/pdb-type-server-simple-b.yaml -o b.obj
RUN: llvm-pdbutil yaml2pdb %S/Inputs/pdb-type-server-simple-ts.yaml -pdb ts.pdb
-RUN: lld-link a.obj b.obj -entry:main -debug -out:t.exe -pdb:t.pdb -nodefaultlib -summary | FileCheck %s -check-prefix SUMMARY
+RUN: lld-link a.obj b.obj -entry:main -debug:noghash -out:t.exe -pdb:t.pdb -nodefaultlib -summary | FileCheck %s -check-prefix SUMMARY
RUN: llvm-pdbutil dump -symbols -types -ids -globals %t/t.pdb | FileCheck %s
Re-run with /DEBUG:GHASH
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