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GlobalOpt only process non constant local GVs while optimizing global vars.

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If non constant local GV named A is used by a constant local GV named B (e.g. llvm.dbg.variable) and B is not used by anyone else then eliminate A as well as B.

In other words, debug info should not interfere in removal of unused GV.
--This life, and those below, will be ignored--

M    test/Transforms/GlobalOpt/2009-03-03-dbg.ll
M    lib/Transforms/IPO/GlobalOpt.cpp


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@66167 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Devang Patel 2009-03-05 18:12:02 +00:00
parent 30a31ebf7f
commit 5049600672
2 changed files with 31 additions and 10 deletions
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40
lib/Transforms/IPO/GlobalOpt.cpp
View File

@ -137,17 +137,28 @@ struct VISIBILITY_HIDDEN GlobalStatus {
}
/// ConstantIsDead - Return true if the specified constant is (transitively)
/// dead. The constant may be used by other constants (e.g. constant arrays and
/// constant exprs) as long as they are dead, but it cannot be used by anything
/// else.
static bool ConstantIsDead(Constant *C) {
/// dead. The constant may be used by other constants (e.g. constant arrays,
/// constant exprs, constant global variables) as long as they are dead,
/// but it cannot be used by anything else. If DeadGVs is not null then
/// record dead constant GV users.
static bool ConstantIsDead(Constant *C,
SmallPtrSet<GlobalVariable *, 4> *DeadGVs = false) {
if (isa<GlobalValue>(C)) return false;
for (Value::use_iterator UI = C->use_begin(), E = C->use_end(); UI != E; ++UI)
if (Constant *CU = dyn_cast<Constant>(*UI)) {
if (!ConstantIsDead(CU)) return false;
for (Value::use_iterator UI = C->use_begin(), E = C->use_end(); UI != E; ++UI) {
if (GlobalVariable *GV = dyn_cast<GlobalVariable>(*UI)) {
if (!GV->isConstant() || !GV->hasLocalLinkage() || !GV->use_empty())
return false;
else {
if (DeadGVs)
DeadGVs->insert(GV);
}
}
else if (Constant *CU = dyn_cast<Constant>(*UI)) {
if (!ConstantIsDead(CU, DeadGVs)) return false;
} else
return false;
}
return true;
}
@ -338,8 +349,19 @@ static bool CleanupConstantGlobalUsers(Value *V, Constant *Init) {
} else if (Constant *C = dyn_cast<Constant>(U)) {
// If we have a chain of dead constantexprs or other things dangling from
// us, and if they are all dead, nuke them without remorse.
if (ConstantIsDead(C)) {
C->destroyConstant();
SmallPtrSet<GlobalVariable *, 4> DeadGVs;
if (ConstantIsDead(C, &DeadGVs)) {
for (SmallPtrSet<GlobalVariable *, 4>::iterator TI = DeadGVs.begin(),
TE = DeadGVs.end(); TI != TE; ) {
GlobalVariable *TGV = *TI; ++TI;
if (TGV == C)
C = NULL;
TGV->eraseFromParent();
}
if (GlobalVariable *GV = dyn_cast<GlobalVariable>(C))
GV->eraseFromParent();
else if (C)
C->destroyConstant();
// This could have invalidated UI, start over from scratch.
CleanupConstantGlobalUsers(V, Init);
return true;

1
test/Transforms/GlobalOpt/2009-03-03-dbg.ll
View File

@ -1,5 +1,4 @@
; RUN: llvm-as < %s | opt -globalopt | llvm-dis | not grep global_variable42
; XFAIL: *
%llvm.dbg.anchor.type = type { i32, i32 }
%llvm.dbg.basictype.type = type { i32, { }*, i8*, { }*, i32, i64, i64, i64, i32, i32 }