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Delete unused global aliases with internal linkage.

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In fact this also deletes those with linkonce linkage,
however this is currently dead because for the moment
aliases aren't allowed to have this linkage type.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@61742 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Duncan Sands 2009-01-05 20:37:33 +00:00
parent f421533661
commit 1da5f2dd2e
2 changed files with 31 additions and 8 deletions
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31
lib/Transforms/IPO/GlobalDCE.cpp
View File

@ -25,6 +25,7 @@
#include <set>
using namespace llvm;
STATISTIC(NumAliases, "Number of global aliases removed");
STATISTIC(NumFunctions, "Number of functions removed");
STATISTIC(NumVariables, "Number of global variables removed");
@ -32,7 +33,7 @@ namespace {
struct VISIBILITY_HIDDEN GlobalDCE : public ModulePass {
static char ID; // Pass identification, replacement for typeid
GlobalDCE() : ModulePass(&ID) {}
// run - Do the GlobalDCE pass on the specified module, optionally updating
// the specified callgraph to reflect the changes.
//
@ -41,7 +42,7 @@ namespace {
private:
std::set<GlobalValue*> AliveGlobals;
/// GlobalIsNeeded - the specific global value as needed, and
/// GlobalIsNeeded - mark the specific global value as needed, and
/// recursively mark anything that it uses as also needed.
void GlobalIsNeeded(GlobalValue *GV);
void MarkUsedGlobalsAsNeeded(Constant *C);
@ -77,11 +78,12 @@ bool GlobalDCE::runOnModule(Module &M) {
GlobalIsNeeded(I);
}
for (Module::alias_iterator I = M.alias_begin(), E = M.alias_end();
I != E; ++I) {
// Aliases are always needed even if they are not used.
MarkUsedGlobalsAsNeeded(I->getAliasee());
Changed |= RemoveUnusedGlobalValue(*I);
// Externally visible aliases are needed.
if (!I->hasInternalLinkage() && !I->hasLinkOnceLinkage())
GlobalIsNeeded(I);
}
// Now that all globals which are needed are in the AliveGlobals set, we loop
@ -96,7 +98,6 @@ bool GlobalDCE::runOnModule(Module &M) {
I->setInitializer(0);
}
// The second pass drops the bodies of functions which are dead...
std::vector<Function*> DeadFunctions;
for (Module::iterator I = M.begin(), E = M.end(); I != E; ++I)
@ -107,7 +108,7 @@ bool GlobalDCE::runOnModule(Module &M) {
}
if (!DeadFunctions.empty()) {
// Now that all interreferences have been dropped, delete the actual objects
// Now that all interferences have been dropped, delete the actual objects
// themselves.
for (unsigned i = 0, e = DeadFunctions.size(); i != e; ++i) {
RemoveUnusedGlobalValue(*DeadFunctions[i]);
@ -126,6 +127,17 @@ bool GlobalDCE::runOnModule(Module &M) {
Changed = true;
}
// Now delete any dead aliases.
for (Module::alias_iterator I = M.alias_begin(), E = M.alias_end(); I != E;) {
Module::alias_iterator J = I++;
if (!AliveGlobals.count(J)) {
RemoveUnusedGlobalValue(*J);
M.getAliasList().erase(J);
++NumAliases;
Changed = true;
}
}
// Make sure that all memory is released
AliveGlobals.clear();
return Changed;
@ -147,7 +159,10 @@ void GlobalDCE::GlobalIsNeeded(GlobalValue *G) {
// referenced by the initializer to the alive set.
if (GV->hasInitializer())
MarkUsedGlobalsAsNeeded(GV->getInitializer());
} else if (!isa<GlobalAlias>(G)) {
} else if (GlobalAlias *GA = dyn_cast<GlobalAlias>(G)) {
// The target of a global alias is needed.
MarkUsedGlobalsAsNeeded(GA->getAliasee());
} else {
// Otherwise this must be a function object. We have to scan the body of
// the function looking for constants and global values which are used as
// operands. Any operands of these types must be processed to ensure that

8
test/Transforms/GlobalDCE/2009-01-05-DeadAliases.ll Normal file
View File

@ -0,0 +1,8 @@
; RUN: llvm-as < %s | opt -globaldce | llvm-dis | not grep @D
; RUN: llvm-as < %s | opt -globaldce | llvm-dis | grep @L | count 3
@A = global i32 0
@D = alias internal i32* @A
@L1 = alias i32* @A
@L2 = alias internal i32* @L1
@L3 = alias i32* @L2