[PATCH] D120052: [GlobalDCE] Simplify and return Changed = true less often

[Jay Foad via Phabricator via llvm-commits]

foad created this revision.
foad added reviewers: lebedev.ri, serge-sans-paille, piotr.
Herald added subscribers: ormris, hiraditya.
foad requested review of this revision.
Herald added a project: LLVM.
Herald added a subscriber: llvm-commits.

Removing dead constants should not count as making a change to the
module. This means that RemoveUnusedGlobalValue simplifies to just
calling removeDeadConstantUsers, so inline it.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D120052

Files:
  llvm/lib/Transforms/IPO/GlobalDCE.cpp


Index: llvm/lib/Transforms/IPO/GlobalDCE.cpp
===================================================================
--- llvm/lib/Transforms/IPO/GlobalDCE.cpp
+++ llvm/lib/Transforms/IPO/GlobalDCE.cpp
@@ -317,7 +317,7 @@
 
   // Loop over the module, adding globals which are obviously necessary.
   for (GlobalObject &GO : M.global_objects()) {
-    Changed |= RemoveUnusedGlobalValue(GO);
+    GO.removeDeadConstantUsers();
     // Functions with external linkage are needed if they have a body.
     // Externally visible & appending globals are needed, if they have an
     // initializer.
@@ -330,7 +330,7 @@
 
   // Compute direct dependencies of aliases.
   for (GlobalAlias &GA : M.aliases()) {
-    Changed |= RemoveUnusedGlobalValue(GA);
+    GA.removeDeadConstantUsers();
     // Externally visible aliases are needed.
     if (!GA.isDiscardableIfUnused())
       MarkLive(GA);
@@ -340,7 +340,7 @@
 
   // Compute direct dependencies of ifuncs.
   for (GlobalIFunc &GIF : M.ifuncs()) {
-    Changed |= RemoveUnusedGlobalValue(GIF);
+    GIF.removeDeadConstantUsers();
     // Externally visible ifuncs are needed.
     if (!GIF.isDiscardableIfUnused())
       MarkLive(GIF);
@@ -403,7 +403,7 @@
   // Now that all interferences have been dropped, delete the actual objects
   // themselves.
   auto EraseUnusedGlobalValue = [&](GlobalValue *GV) {
-    RemoveUnusedGlobalValue(*GV);
+    GV->removeDeadConstantUsers();
     GV->eraseFromParent();
     Changed = true;
   };
@@ -455,16 +455,3 @@
     return PreservedAnalyses::none();
   return PreservedAnalyses::all();
 }
-
-// RemoveUnusedGlobalValue - Loop over all of the uses of the specified
-// GlobalValue, looking for the constant pointer ref that may be pointing to it.
-// If found, check to see if the constant pointer ref is safe to destroy, and if
-// so, nuke it.  This will reduce the reference count on the global value, which
-// might make it deader.
-//
-bool GlobalDCEPass::RemoveUnusedGlobalValue(GlobalValue &GV) {
-  if (GV.use_empty())
-    return false;
-  GV.removeDeadConstantUsers();
-  return GV.use_empty();
-}


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