6502/llvm-6502
1
0
Fork 0
mirror of https://github.com/c64scene-ar/llvm-6502.git synced 2024-10-01 10:57:21 +00:00
Code Issues Projects Releases Wiki Activity

GlobalDCE: Improve performance for large modules containing comdats.

Browse Source 
When we encounter a global with a comdat, rather than iterating over
every global in the module to find globals in the same comdat, store the
members in a multimap. This effectively lowers the complexity to O(N log N),
improving performance significantly for large modules such as might be
encountered during LTO.

It looks like we used to do something like this until r219191.

No functional change.

Differential Revision: http://reviews.llvm.org/D8431

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@232743 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Peter Collingbourne 2015-03-19 18:23:29 +00:00
parent 6e2749c772
commit c226d9f334
1 changed files with 16 additions and 10 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

26
lib/Transforms/IPO/GlobalDCE.cpp
View File

@ -24,6 +24,7 @@
#include "llvm/Transforms/Utils/CtorUtils.h"
#include "llvm/Transforms/Utils/GlobalStatus.h"
#include "llvm/Pass.h"
#include <unordered_map>
using namespace llvm;
#define DEBUG_TYPE "globaldce"
@ -47,6 +48,7 @@ namespace {
private:
SmallPtrSet<GlobalValue*, 32> AliveGlobals;
SmallPtrSet<Constant *, 8> SeenConstants;
std::unordered_multimap<Comdat *, GlobalValue *> ComdatMembers;
/// GlobalIsNeeded - mark the specific global value as needed, and
/// recursively mark anything that it uses as also needed.
@ -78,6 +80,17 @@ bool GlobalDCE::runOnModule(Module &M) {
// Remove empty functions from the global ctors list.
Changed |= optimizeGlobalCtorsList(M, isEmptyFunction);
// Collect the set of members for each comdat.
for (Function &F : M)
if (Comdat *C = F.getComdat())
ComdatMembers.insert(std::make_pair(C, &F));
for (GlobalVariable &GV : M.globals())
if (Comdat *C = GV.getComdat())
ComdatMembers.insert(std::make_pair(C, &GV));
for (GlobalAlias &GA : M.aliases())
if (Comdat *C = GA.getComdat())
ComdatMembers.insert(std::make_pair(C, &GA));
// Loop over the module, adding globals which are obviously necessary.
for (Module::iterator I = M.begin(), E = M.end(); I != E; ++I) {
Changed |= RemoveUnusedGlobalValue(*I);
@ -177,6 +190,7 @@ bool GlobalDCE::runOnModule(Module &M) {
// Make sure that all memory is released
AliveGlobals.clear();
SeenConstants.clear();
ComdatMembers.clear();
return Changed;
}
@ -188,17 +202,9 @@ void GlobalDCE::GlobalIsNeeded(GlobalValue *G) {
if (!AliveGlobals.insert(G).second)
return;
Module *M = G->getParent();
if (Comdat *C = G->getComdat()) {
for (Function &F : *M)
if (F.getComdat() == C)
GlobalIsNeeded(&F);
for (GlobalVariable &GV : M->globals())
if (GV.getComdat() == C)
GlobalIsNeeded(&GV);
for (GlobalAlias &GA : M->aliases())
if (GA.getComdat() == C)
GlobalIsNeeded(&GA);
for (auto &&CM : make_range(ComdatMembers.equal_range(C)))
GlobalIsNeeded(CM.second);
}
if (GlobalVariable *GV = dyn_cast<GlobalVariable>(G)) {