Don't merge two constants if we care about the address of both.
This fixes the original testcase in PR8927. It also causes a clang
binary built with a patched clang to increase in size by 0.21%.
We can probably get some of the size back by writing a pass that
detects that a global never has its pointer compared and adds
unnamed_addr to it (maybe extend global opt). It is also possible that
there are some other cases clang could add unnamed_addr to.
I will investigate extending globalopt next.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@123584 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Transforms/IPO/ConstantMerge.cpp b/lib/Transforms/IPO/ConstantMerge.cpp
index 6b62f3b..a21efce 100644
--- a/lib/Transforms/IPO/ConstantMerge.cpp
+++ b/lib/Transforms/IPO/ConstantMerge.cpp
@@ -65,6 +65,18 @@
UsedValues.insert(GV);
}
+// True if A is better than B.
+static bool IsBetterCannonical(const GlobalVariable &A,
+ const GlobalVariable &B) {
+ if (!A.hasLocalLinkage() && B.hasLocalLinkage())
+ return true;
+
+ if (A.hasLocalLinkage() && !B.hasLocalLinkage())
+ return false;
+
+ return A.hasUnnamedAddr();
+}
+
bool ConstantMerge::runOnModule(Module &M) {
// Find all the globals that are marked "used". These cannot be merged.
SmallPtrSet<const GlobalValue*, 8> UsedGlobals;
@@ -85,44 +97,43 @@
// second level constants have initializers which point to the globals that
// were just merged.
while (1) {
- // First pass: identify all globals that can be merged together, filling in
- // the Replacements vector. We cannot do the replacement in this pass
- // because doing so may cause initializers of other globals to be rewritten,
- // invalidating the Constant* pointers in CMap.
- //
+
+ // First: Find the canonical constants others will be merged with.
for (Module::global_iterator GVI = M.global_begin(), E = M.global_end();
GVI != E; ) {
GlobalVariable *GV = GVI++;
-
+
// If this GV is dead, remove it.
GV->removeDeadConstantUsers();
if (GV->use_empty() && GV->hasLocalLinkage()) {
GV->eraseFromParent();
continue;
}
-
+
// Only process constants with initializers in the default address space.
if (!GV->isConstant() || !GV->hasDefinitiveInitializer() ||
GV->getType()->getAddressSpace() != 0 || GV->hasSection() ||
// Don't touch values marked with attribute(used).
UsedGlobals.count(GV))
continue;
-
- // Start by filling slots with only the globals we aren't allowed to
- // delete because they're externally visible.
- if (GV->hasLocalLinkage())
- continue;
-
+
Constant *Init = GV->getInitializer();
// Check to see if the initializer is already known.
GlobalVariable *&Slot = CMap[Init];
- if (Slot == 0) { // Nope, add it to the map.
+ // If this is the first constant we find or if the old on is local,
+ // replace with the current one. It the current is externally visible
+ // it cannot be replace, but can be the canonical constant we merge with.
+ if (Slot == 0 || IsBetterCannonical(*GV, *Slot)) {
Slot = GV;
}
}
+ // Second: identify all globals that can be merged together, filling in
+ // the Replacements vector. We cannot do the replacement in this pass
+ // because doing so may cause initializers of other globals to be rewritten,
+ // invalidating the Constant* pointers in CMap.
for (Module::global_iterator GVI = M.global_begin(), E = M.global_end();
GVI != E; ) {
GlobalVariable *GV = GVI++;
@@ -134,21 +145,26 @@
UsedGlobals.count(GV))
continue;
- // Only look at the remaining globals now.
+ // We can only replace constant with local linkage.
if (!GV->hasLocalLinkage())
continue;
Constant *Init = GV->getInitializer();
// Check to see if the initializer is already known.
- GlobalVariable *&Slot = CMap[Init];
+ GlobalVariable *Slot = CMap[Init];
- if (Slot == 0) { // Nope, add it to the map.
- Slot = GV;
- } else { // Yup, this is a duplicate!
- // Make all uses of the duplicate constant use the canonical version.
- Replacements.push_back(std::make_pair(GV, Slot));
- }
+ if (!Slot || Slot == GV)
+ continue;
+
+ if (!Slot->hasUnnamedAddr() && !GV->hasUnnamedAddr())
+ continue;
+
+ if (!GV->hasUnnamedAddr())
+ Slot->setUnnamedAddr(false);
+
+ // Make all uses of the duplicate constant use the canonical version.
+ Replacements.push_back(std::make_pair(GV, Slot));
}
if (Replacements.empty())