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Rework GlobalValue::removeDeadConstantUsers to always remove dead constant

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exprs hanging off a global, even if the global is not otherwise dead.  This
requires some tricky iterator gymnastics.

This implements Transforms/GlobalOpt/constantexpr-dangle.ll by deleting a
constantexpr that made it appear that the address of the function was taken.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@34608 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Chris Lattner 2007-02-25 21:06:13 +00:00
parent 2aef09a06b
commit 1cf5574636
2 changed files with 29 additions and 25 deletions
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4
include/llvm/GlobalValue.h
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@ -128,10 +128,6 @@ public:
/// off of this global value, remove them. This method is useful for clients
/// that want to check to see if a global is unused, but don't want to deal
/// with potentially dead constants hanging off of the globals.
///
/// This method tries to make the global dead. If it detects a user that
/// would prevent it from becoming completely dead, it gives up early,
/// potentially leaving some dead constant users around.
void removeDeadConstantUsers();
// Methods for support type inquiry through isa, cast, and dyn_cast:

50
lib/VMCore/Globals.cpp
View File

@ -22,20 +22,18 @@ using namespace llvm;
// GlobalValue Class
//===----------------------------------------------------------------------===//
/// This could be named "SafeToDestroyGlobalValue". It just makes sure that
/// there are no non-constant uses of this GlobalValue. If there aren't then
/// this and the transitive closure of the constants can be deleted. See the
/// destructor for details.
static bool removeDeadConstantUsers(Constant* C) {
/// removeDeadUsersOfConstant - If the specified constantexpr is dead, remove
/// it. This involves recursively eliminating any dead users of the
/// constantexpr.
static bool removeDeadUsersOfConstant(Constant *C) {
if (isa<GlobalValue>(C)) return false; // Cannot remove this
while (!C->use_empty())
if (Constant *User = dyn_cast<Constant>(C->use_back())) {
if (!removeDeadConstantUsers(User))
return false; // Constant wasn't dead
} else {
return false; // Non-constant usage;
}
while (!C->use_empty()) {
Constant *User = dyn_cast<Constant>(C->use_back());
if (!User) return false; // Non-constant usage;
if (!removeDeadUsersOfConstant(User))
return false; // Constant wasn't dead
}
C->destroyConstant();
return true;
@ -45,17 +43,27 @@ static bool removeDeadConstantUsers(Constant* C) {
/// off of this global value, remove them. This method is useful for clients
/// that want to check to see if a global is unused, but don't want to deal
/// with potentially dead constants hanging off of the globals.
///
/// This function returns true if the global value is now dead. If all
/// users of this global are not dead, this method may return false and
/// leave some of them around.
void GlobalValue::removeDeadConstantUsers() {
while(!use_empty()) {
if (Constant* User = dyn_cast<Constant>(use_back())) {
if (!::removeDeadConstantUsers(User))
return; // Constant wasn't dead
Value::use_iterator I = use_begin(), E = use_end();
Value::use_iterator LastNonDeadUser = E;
for (; I != E; ++I) {
if (Constant *User = dyn_cast<Constant>(*I)) {
if (!removeDeadUsersOfConstant(User)) {
// If the constant wasn't dead, remember that this was the last live use
// and move on to the next constant.
LastNonDeadUser = I;
} else {
// If the constant was dead, then the iterator is invalidated.
if (LastNonDeadUser == E) {
I = use_begin();
if (I == E) break;
} else {
I = LastNonDeadUser;
}
}
} else {
return; // Non-constant usage;
LastNonDeadUser = I;
}
}
}