[llvm] llvm-reduce: Simplify instruction reduction to avoid worklist (PR #133391)

[Matt Arsenault via llvm-commits]

https://github.com/arsenm created https://github.com/llvm/llvm-project/pull/133391

None

>From 78ecca4c1999375875f8cc53cafbce2029b8f8a0 Mon Sep 17 00:00:00 2001
From: Matt Arsenault <Matthew.Arsenault at amd.com>
Date: Fri, 28 Mar 2025 14:38:56 +0700
Subject: [PATCH] llvm-reduce: Simplify instruction reduction to avoid worklist

---
 .../llvm-reduce/deltas/ReduceInstructions.cpp | 32 +++++--------------
 1 file changed, 8 insertions(+), 24 deletions(-)

diff --git a/llvm/tools/llvm-reduce/deltas/ReduceInstructions.cpp b/llvm/tools/llvm-reduce/deltas/ReduceInstructions.cpp
index 9917fed000b7a..e1b7924594b5e 100644
--- a/llvm/tools/llvm-reduce/deltas/ReduceInstructions.cpp
+++ b/llvm/tools/llvm-reduce/deltas/ReduceInstructions.cpp
@@ -31,36 +31,20 @@ static bool shouldAlwaysKeep(const Instruction &I) {
 /// accordingly. It also removes allocations of out-of-chunk arguments.
 static void extractInstrFromModule(Oracle &O, ReducerWorkItem &WorkItem) {
   Module &Program = WorkItem.getModule();
-  std::vector<Instruction *> InitInstToKeep;
 
-  for (auto &F : Program)
+  for (auto &F : Program) {
     for (auto &BB : F) {
       // Removing the terminator would make the block invalid. Only iterate over
       // instructions before the terminator.
-      InitInstToKeep.push_back(BB.getTerminator());
-      for (auto &Inst : make_range(BB.begin(), std::prev(BB.end()))) {
-        if (shouldAlwaysKeep(Inst) || O.shouldKeep())
-          InitInstToKeep.push_back(&Inst);
-      }
-    }
-
-  // We create a vector first, then convert it to a set, so that we don't have
-  // to pay the cost of rebalancing the set frequently if the order we insert
-  // the elements doesn't match the order they should appear inside the set.
-  std::set<Instruction *> InstToKeep(InitInstToKeep.begin(),
-                                     InitInstToKeep.end());
-
-  std::vector<Instruction *> InstToDelete;
-  for (auto &F : Program)
-    for (auto &BB : F)
-      for (auto &Inst : BB)
-        if (!InstToKeep.count(&Inst)) {
+      for (auto &Inst :
+           make_early_inc_range(make_range(BB.begin(), std::prev(BB.end())))) {
+        if (!shouldAlwaysKeep(Inst) && !O.shouldKeep()) {
           Inst.replaceAllUsesWith(getDefaultValue(Inst.getType()));
-          InstToDelete.push_back(&Inst);
+          Inst.eraseFromParent();
         }
-
-  for (auto &I : InstToDelete)
-    I->eraseFromParent();
+      }
+    }
+  }
 }
 
 void llvm::reduceInstructionsDeltaPass(TestRunner &Test) {