Revert "[Inline][Cloning] Defer simplification after phi-nodes resolution" #87963

Reopens #87534.

Breaks multiple bots:
https://lab.llvm.org/buildbot/#/builders/168/builds/20028
https://lab.llvm.org/buildbot/#/builders/74/builds/27773

And reproducer in a61f9fe.

This reverts commit a61f9fe.

Author: vitalybuka

llvm/lib/Transforms/Utils/CloneFunction.cpp

@@ -14,7 +14,6 @@
 
 #include "llvm/ADT/SetVector.h"
 #include "llvm/ADT/SmallVector.h"
-#include "llvm/Analysis/ConstantFolding.h"
 #include "llvm/Analysis/DomTreeUpdater.h"
 #include "llvm/Analysis/InstructionSimplify.h"
 #include "llvm/Analysis/LoopInfo.h"
@@ -541,13 +540,18 @@ void PruningFunctionCloner::CloneBlock(
       RemapInstruction(NewInst, VMap,
                        ModuleLevelChanges ? RF_None : RF_NoModuleLevelChanges);
 
-      // Eagerly constant fold the newly cloned instruction. If successful, add
-      // a mapping to the new value. Non-constant operands may be incomplete at
-      // this stage, thus instruction simplification is performed after
-      // processing phi-nodes.
-      if (Value *V = ConstantFoldInstruction(
-              NewInst, BB->getModule()->getDataLayout())) {
-        if (isInstructionTriviallyDead(NewInst)) {
+      // If we can simplify this instruction to some other value, simply add
+      // a mapping to that value rather than inserting a new instruction into
+      // the basic block.
+      if (Value *V =
+              simplifyInstruction(NewInst, BB->getModule()->getDataLayout())) {
+        // On the off-chance that this simplifies to an instruction in the old
+        // function, map it back into the new function.
+        if (NewFunc != OldFunc)
+          if (Value *MappedV = VMap.lookup(V))
+            V = MappedV;
+
+        if (!NewInst->mayHaveSideEffects()) {
           VMap[&*II] = V;
           NewInst->eraseFromParent();
           continue;
@@ -819,34 +823,52 @@ void llvm::CloneAndPruneIntoFromInst(Function *NewFunc, const Function *OldFunc,
     }
   }
 
-  // As phi-nodes have been now remapped, allow incremental simplification of
-  // newly-cloned instructions.
+  // Make a second pass over the PHINodes now that all of them have been
+  // remapped into the new function, simplifying the PHINode and performing any
+  // recursive simplifications exposed. This will transparently update the
+  // WeakTrackingVH in the VMap. Notably, we rely on that so that if we coalesce
+  // two PHINodes, the iteration over the old PHIs remains valid, and the
+  // mapping will just map us to the new node (which may not even be a PHI
+  // node).
   const DataLayout &DL = NewFunc->getParent()->getDataLayout();
-  for (const auto &BB : *OldFunc) {
-    for (const auto &I : BB) {
-      auto *NewI = dyn_cast_or_null<Instruction>(VMap.lookup(&I));
-      if (!NewI)
-        continue;
-
-      // Skip over non-intrinsic callsites, we don't want to remove any nodes
-      // from the CGSCC.
-      CallBase *CB = dyn_cast<CallBase>(NewI);
-      if (CB && CB->getCalledFunction() &&
-          !CB->getCalledFunction()->isIntrinsic())
-        continue;
-
-      if (Value *V = simplifyInstruction(NewI, DL)) {
-        NewI->replaceAllUsesWith(V);
-
-        if (isInstructionTriviallyDead(NewI)) {
-          NewI->eraseFromParent();
-        } else {
-          // Did not erase it? Restore the new instruction into VMap previously
-          // dropped by `ValueIsRAUWd`.
-          VMap[&I] = NewI;
-        }
-      }
-    }
+  SmallSetVector<const Value *, 8> Worklist;
+  for (unsigned Idx = 0, Size = PHIToResolve.size(); Idx != Size; ++Idx)
+    if (isa<PHINode>(VMap[PHIToResolve[Idx]]))
+      Worklist.insert(PHIToResolve[Idx]);
+
+  // Note that we must test the size on each iteration, the worklist can grow.
+  for (unsigned Idx = 0; Idx != Worklist.size(); ++Idx) {
+    const Value *OrigV = Worklist[Idx];
+    auto *I = dyn_cast_or_null<Instruction>(VMap.lookup(OrigV));
+    if (!I)
+      continue;
+
+    // Skip over non-intrinsic callsites, we don't want to remove any nodes from
+    // the CGSCC.
+    CallBase *CB = dyn_cast<CallBase>(I);
+    if (CB && CB->getCalledFunction() &&
+        !CB->getCalledFunction()->isIntrinsic())
+      continue;
+
+    // See if this instruction simplifies.
+    Value *SimpleV = simplifyInstruction(I, DL);
+    if (!SimpleV)
+      continue;
+
+    // Stash away all the uses of the old instruction so we can check them for
+    // recursive simplifications after a RAUW. This is cheaper than checking all
+    // uses of To on the recursive step in most cases.
+    for (const User *U : OrigV->users())
+      Worklist.insert(cast<Instruction>(U));
+
+    // Replace the instruction with its simplified value.
+    I->replaceAllUsesWith(SimpleV);
+
+    // If the original instruction had no side effects, remove it.
+    if (isInstructionTriviallyDead(I))
+      I->eraseFromParent();
+    else
+      VMap[OrigV] = I;
   }
 
   // Remap debug intrinsic operands now that all values have been mapped.

llvm/test/Transforms/Inline/inline-deferred-instsimplify.ll

@@ -38,6 +38,8 @@ store_ptr_in_gvar:                                ; preds = %entry
 
 check_pointers_are_equal:                         ; preds = %store_ptr_in_gvar, %entry
   %phi = phi ptr [ %ptr, %store_ptr_in_gvar ], [ @other_g_var, %entry ]
+; FIXME: While inlining, the following is miscompiled to i1 false,
+; as %ptr in the phi-node is not taken into account.
   %.not1 = icmp eq ptr %phi, %ptr
   br i1 %.not1, label %return, label %abort
 
@@ -62,13 +64,9 @@ define i32 @main() {
 ; CHECK-NEXT:    br label [[CHECK_POINTERS_ARE_EQUAL_I]]
 ; CHECK:       check_pointers_are_equal.i:
 ; CHECK-NEXT:    [[PHI_I:%.*]] = phi ptr [ [[G_VAR]], [[STORE_PTR_IN_GVAR_I]] ], [ @other_g_var, [[TMP0:%.*]] ]
-; CHECK-NEXT:    [[DOTNOT1_I:%.*]] = icmp eq ptr [[PHI_I]], [[G_VAR]]
-; CHECK-NEXT:    br i1 [[DOTNOT1_I]], label [[CALLEE_EXIT:%.*]], label [[ABORT_I:%.*]]
-; CHECK:       abort.i:
 ; CHECK-NEXT:    call void @abort()
 ; CHECK-NEXT:    unreachable
 ; CHECK:       callee.exit:
-; CHECK-NEXT:    call void @llvm.lifetime.end.p0(i64 20, ptr [[G_VAR]])
 ; CHECK-NEXT:    ret i32 0
 ;
   call void @callee(ptr noundef byval(%struct.a) align 8 @g_var)

llvm/test/Transforms/Inline/prof-update-sample-alwaysinline.ll

@@ -53,6 +53,7 @@ define void @caller() {
 !18 = !{!"VP", i32 0, i64 140, i64 111, i64 80, i64 222, i64 40, i64 333, i64 20}
 attributes #0 = { alwaysinline }
 ; CHECK: ![[ENTRY_COUNT]] = !{!"function_entry_count", i64 600}
+; CHECK: ![[COUNT_CALLEE1]] = !{!"branch_weights", i32 2000}
 ; CHECK: ![[COUNT_CALLEE]] = !{!"branch_weights", i32 1200}
 ; CHECK: ![[COUNT_IND_CALLEE]] = !{!"VP", i32 0, i64 84, i64 111, i64 48, i64 222, i64 24, i64 333, i64 12}
 ; CHECK: ![[COUNT_CALLER]] = !{!"branch_weights", i32 800}

llvm/test/Transforms/Inline/prof-update-sample.ll

@@ -52,6 +52,7 @@ define void @caller() {
 !17 = !{!"branch_weights", i32 400}
 !18 = !{!"VP", i32 0, i64 140, i64 111, i64 80, i64 222, i64 40, i64 333, i64 20}
 ; CHECK: ![[ENTRY_COUNT]] = !{!"function_entry_count", i64 600}
+; CHECK: ![[COUNT_CALLEE1]] = !{!"branch_weights", i32 2000}
 ; CHECK: ![[COUNT_CALLEE]] = !{!"branch_weights", i32 1200}
 ; CHECK: ![[COUNT_IND_CALLEE]] = !{!"VP", i32 0, i64 84, i64 111, i64 48, i64 222, i64 24, i64 333, i64 12}
 ; CHECK: ![[COUNT_CALLER]] = !{!"branch_weights", i32 800}