ephemeral.patch

commit c92757dc7630597e608c83238f79b4983ea43553
Author: Nikita Popov <nikita.ppv@gmail.com>
Date:   Tue Oct 19 21:05:09 2021 +0200

    ephemeral

diff --git a/llvm/lib/Analysis/CodeMetrics.cpp b/llvm/lib/Analysis/CodeMetrics.cpp
index 8c8e2ee6627f..27c52506352f 100644
--- a/llvm/lib/Analysis/CodeMetrics.cpp
+++ b/llvm/lib/Analysis/CodeMetrics.cpp
@@ -34,8 +34,9 @@ appendSpeculatableOperands(const Value *V,
 
   for (const Value *Operand : U->operands())
     if (Visited.insert(Operand).second)
-      if (isSafeToSpeculativelyExecute(Operand))
-        Worklist.push_back(Operand);
+      if (const auto *I = dyn_cast<Instruction>(Operand))
+        if (!I->mayHaveSideEffects() && !I->isTerminator())
+          Worklist.push_back(I);
 }
 
 static void completeEphemeralValues(SmallPtrSetImpl<const Value *> &Visited,
diff --git a/llvm/lib/Analysis/ValueTracking.cpp b/llvm/lib/Analysis/ValueTracking.cpp
index bf1989c58c20..8991582a7a25 100644
--- a/llvm/lib/Analysis/ValueTracking.cpp
+++ b/llvm/lib/Analysis/ValueTracking.cpp
@@ -494,7 +494,9 @@ static bool isEphemeralValueOf(const Instruction *I, const Value *E) {
       if (V == E)
         return true;
 
-      if (V == I || isSafeToSpeculativelyExecute(V)) {
+      if (V == I || (isa<Instruction>(V) &&
+                     !cast<Instruction>(V)->mayHaveSideEffects() &&
+                     !cast<Instruction>(V)->isTerminator())) {
        EphValues.insert(V);
        if (const User *U = dyn_cast<User>(V))
          append_range(WorkSet, U->operands());
diff --git a/llvm/lib/Transforms/Utils/SimplifyCFG.cpp b/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
index 920df4e9d742..84bf364d6d24 100644
--- a/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
+++ b/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
@@ -2577,11 +2577,11 @@ static bool BlockIsSimpleEnoughToThreadThrough(BasicBlock *BB) {
   int Size = 0;
 
   SmallPtrSet<const Value *, 32> EphValues;
-  auto IsEphemeral = [&](const Value *V) {
-    if (isa<AssumeInst>(V))
+  auto IsEphemeral = [&](const Instruction *I) {
+    if (isa<AssumeInst>(I))
       return true;
-    return isSafeToSpeculativelyExecute(V) &&
-           all_of(V->users(),
+    return !I->mayHaveSideEffects() && !I->isTerminator() &&
+           all_of(I->users(),
                   [&](const User *U) { return EphValues.count(U); });
   };