[llvm-reduce] extractGVsFromModule(): don't crash when deleting instr…

… twice

As it can be seen in newly-added (previously-crashing) test-case,
there can be a situation where multiple GV's are used in instr,
and we would schedule the same instruction to be deleted several times,
crashing when trying to delete it the second time.

We could either store WeakVH (done here), or use something set-like.
I think using WeakVH is prevalent in these cases elsewhere.

llvm/test/Reduce/Inputs/remove-multiple-use-of-global-vars-in-same-instruction.py

@@ -0,0 +1,13 @@
+import sys
+
+FunctionCallPresent = False
+
+input = open(sys.argv[1], "r")
+for line in input:
+  if "call void @use" in line:
+    FunctionCallPresent = True
+
+if FunctionCallPresent:
+  sys.exit(0) # Interesting!
+
+sys.exit(1)

llvm/test/Reduce/remove-multiple-use-of-global-vars-in-same-instruction.ll

@@ -0,0 +1,24 @@
+; Test that llvm-reduce can remove uninteresting function arguments from function definitions as well as their calls.
+;
+; RUN: rm -rf %t
+; RUN: llvm-reduce --test %python --test-arg %p/Inputs/remove-multiple-use-of-global-vars-in-same-instruction.py %s -o %t
+; RUN: cat %t | FileCheck -implicit-check-not=uninteresting %s
+
+; CHECK: @uninteresting1 = global
+; CHECK: @uninteresting2 = global
+; CHECK: @uninteresting3 = global
+@uninteresting1 = global i32 0, align 4
+@uninteresting2 = global i32 0, align 4
+@uninteresting3 = global i32 0, align 4
+
+declare void @use(i32*, i32*, i32*)
+
+; CHECK-LABEL: @interesting()
+define void @interesting() {
+entry:
+  ; CHECK: call void @use(i32* @uninteresting1, i32* @uninteresting2, i32* @uninteresting3)
+  call void @use(i32* @uninteresting1, i32* @uninteresting2, i32* @uninteresting3)
+  call void @use(i32* @uninteresting1, i32* @uninteresting2, i32* @uninteresting3)
+  call void @use(i32* @uninteresting1, i32* @uninteresting2, i32* @uninteresting3)
+  ret void
+}

llvm/tools/llvm-reduce/deltas/ReduceGlobalVars.cpp

@@ -33,7 +33,7 @@ static void extractGVsFromModule(std::vector<Chunk> ChunksToKeep,
 
   // Delete out-of-chunk GVs and their uses
   std::vector<GlobalVariable *> ToRemove;
-  std::vector<Instruction *> InstToRemove;
+  std::vector<WeakVH> InstToRemove;
   for (auto &GV : Program->globals())
     if (GV.hasInitializer() && !GVsToKeep.count(&GV)) {
       for (auto U : GV.users())
@@ -44,8 +44,11 @@ static void extractGVsFromModule(std::vector<Chunk> ChunksToKeep,
       ToRemove.push_back(&GV);
     }
 
-  // Delete Instruction uses of unwanted GVs
-  for (auto *Inst : InstToRemove) {
+  // Delete (unique) Instruction uses of unwanted GVs
+  for (Value *V : InstToRemove) {
+    if (!V)
+      continue;
+    auto *Inst = cast<Instruction>(V);
     Inst->replaceAllUsesWith(UndefValue::get(Inst->getType()));
     Inst->eraseFromParent();
   }