[PATCH] D85379: Improve dropTriviallyDeadConstantArrays time cost ratio from 17% to 4%

[Stephan Z via Phabricator via llvm-commits]

stephan.yichao.zhao updated this revision to Diff 283510.
stephan.yichao.zhao added a comment.

addressed comments.


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D85379/new/

https://reviews.llvm.org/D85379

Files:
  llvm/lib/IR/LLVMContextImpl.cpp


Index: llvm/lib/IR/LLVMContextImpl.cpp
===================================================================
--- llvm/lib/IR/LLVMContextImpl.cpp
+++ llvm/lib/IR/LLVMContextImpl.cpp
@@ -129,18 +129,24 @@
 }
 
 void LLVMContextImpl::dropTriviallyDeadConstantArrays() {
-  SmallSetVector<ConstantArray *, 4> WorkList(ArrayConstants.begin(),
-                                              ArrayConstants.end());
+  SmallSetVector<ConstantArray *, 4> WorkList;
+
+  // When ArrayConstants are of substantial size and only a few in them are
+  // dead, starting WorkList with all elements of ArrayConstants can be
+  // wasteful. Instead, starting WorkList with only elements that have empty
+  // uses.
+  for (ConstantArray *C : ArrayConstants)
+    if (C->use_empty())
+      WorkList.insert(C);
 
   while (!WorkList.empty()) {
     ConstantArray *C = WorkList.pop_back_val();
-    if (C->use_empty()) {
-      for (const Use &Op : C->operands()) {
-        if (auto *COp = dyn_cast<ConstantArray>(Op))
-          WorkList.insert(COp);
-      }
-      C->destroyConstant();
-    }
+    if (!C->use_empty())
+      continue;
+    for (const Use &Op : C->operands())
+      if (auto *COp = dyn_cast<ConstantArray>(Op))
+        WorkList.insert(COp);
+    C->destroyConstant();
   }
 }
 


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