[InlineCost] Allow simplifying to non-Constant values (NFCI)

[tobias-stadler]

Allow mapping callee Values to arbitrary (non-Constant) simplified values. The simplified values can also originate from the caller. This enables us to simplify instructions in the callee with instructions from the caller.

The first use case for this is simplifying extractvalues (PR #145054).

[llvmbot]

@llvm/pr-subscribers-llvm-analysis

Author: Tobias Stadler (tobias-stadler)

Changes

Allow mapping callee Values to arbitrary (non-Constant) simplified values. The simplified values can also originate from the caller. This enables us to simplify instructions in the callee with instructions from the caller.

The first use case for this is simplifying extractvalues (PR #145054).

---

Full diff: https://github.com/llvm/llvm-project/pull/145083.diff

1 Files Affected:

• (modified) llvm/lib/Analysis/InlineCost.cpp (+51-25)

diff --git a/llvm/lib/Analysis/InlineCost.cpp b/llvm/lib/Analysis/InlineCost.cpp
index 7bd1f18004580..f0ecae758299e 100644
--- a/llvm/lib/Analysis/InlineCost.cpp
+++ b/llvm/lib/Analysis/InlineCost.cpp
@@ -391,7 +391,8 @@ class CallAnalyzer : public InstVisitor<CallAnalyzer, bool> {
   /// likely simplifications post-inlining. The most important aspect we track
   /// is CFG altering simplifications -- when we prove a basic block dead, that
   /// can cause dramatic shifts in the cost of inlining a function.
-  DenseMap<Value *, Constant *> SimplifiedValues;
+  /// Note: The simplified Value may be owned by the caller function.
+  DenseMap<Value *, Value *> SimplifiedValues;
 
   /// Keep track of the values which map back (through function arguments) to
   /// allocas on the caller stack which could be simplified through SROA.
@@ -432,7 +433,7 @@ class CallAnalyzer : public InstVisitor<CallAnalyzer, bool> {
   template <typename T> T *getDirectOrSimplifiedValue(Value *V) const {
     if (auto *Direct = dyn_cast<T>(V))
       return Direct;
-    return dyn_cast_if_present<T>(SimplifiedValues.lookup(V));
+    return getSimplifiedValue<T>(V);
   }
 
   // Custom simplification helper routines.
@@ -525,11 +526,33 @@ class CallAnalyzer : public InstVisitor<CallAnalyzer, bool> {
 
   InlineResult analyze();
 
-  std::optional<Constant *> getSimplifiedValue(Instruction *I) {
-    auto It = SimplifiedValues.find(I);
-    if (It != SimplifiedValues.end())
-      return It->second;
-    return std::nullopt;
+  // Lookup simplified Value. May return a value owned by the caller.
+  Value *getSimplifiedValueUnchecked(Value *V) const {
+    return SimplifiedValues.lookup(V);
+  }
+
+  // Lookup simplified Value, but return nullptr if the simplified value is
+  // owned by the caller.
+  template <typename T> T *getSimplifiedValue(Value *V) const {
+    Value *SimpleV = SimplifiedValues.lookup(V);
+    if (!SimpleV)
+      return nullptr;
+
+    // Skip checks if we know T is a global. This has a small, but measurable
+    // impact on compile-time.
+    if constexpr (std::is_base_of_v<Constant, T>)
+      return dyn_cast<T>(SimpleV);
+
+    // Make sure the simplified Value is owned by this function
+    if (auto *I = dyn_cast<Instruction>(SimpleV)) {
+      if (I->getFunction() != &F)
+        return nullptr;
+    } else if (auto *Arg = dyn_cast<Argument>(SimpleV)) {
+      if (Arg->getParent() != &F)
+        return nullptr;
+    } else if (!isa<Constant>(SimpleV))
+      return nullptr;
+    return dyn_cast<T>(SimpleV);
   }
 
   // Keep a bunch of stats about the cost savings found so we can print them
@@ -921,12 +944,11 @@ class InlineCostCallAnalyzer final : public CallAnalyzer {
         if (BranchInst *BI = dyn_cast<BranchInst>(&I)) {
           // Count a conditional branch as savings if it becomes unconditional.
           if (BI->isConditional() &&
-              isa_and_nonnull<ConstantInt>(
-                  SimplifiedValues.lookup(BI->getCondition()))) {
+              getSimplifiedValue<ConstantInt>(BI->getCondition())) {
             CurrentSavings += InstrCost;
           }
         } else if (SwitchInst *SI = dyn_cast<SwitchInst>(&I)) {
-          if (isa_and_present<ConstantInt>(SimplifiedValues.lookup(SI->getCondition())))
+          if (getSimplifiedValue<ConstantInt>(SI->getCondition()))
             CurrentSavings += InstrCost;
         } else if (Value *V = dyn_cast<Value>(&I)) {
           // Count an instruction as savings if we can fold it.
@@ -1423,10 +1445,17 @@ void InlineCostAnnotationWriter::emitInstructionAnnot(
     if (Record->hasThresholdChanged())
       OS << ", threshold delta = " << Record->getThresholdDelta();
   }
-  auto C = ICCA->getSimplifiedValue(const_cast<Instruction *>(I));
-  if (C) {
+  auto *V = ICCA->getSimplifiedValueUnchecked(const_cast<Instruction *>(I));
+  if (V) {
     OS << ", simplified to ";
-    (*C)->print(OS, true);
+    V->print(OS, true);
+    if (auto *VI = dyn_cast<Instruction>(V)) {
+      if (VI->getFunction() != I->getFunction())
+        OS << " (caller instruction)";
+    } else if (auto *VArg = dyn_cast<Argument>(V)) {
+      if (VArg->getParent() != I->getFunction())
+        OS << " (caller argument)";
+    }
   }
   OS << "\n";
 }
@@ -1483,7 +1512,7 @@ bool CallAnalyzer::isGEPFree(GetElementPtrInst &GEP) {
   SmallVector<Value *, 4> Operands;
   Operands.push_back(GEP.getOperand(0));
   for (const Use &Op : GEP.indices())
-    if (Constant *SimpleOp = SimplifiedValues.lookup(Op))
+    if (Constant *SimpleOp = getSimplifiedValue<Constant>(Op))
       Operands.push_back(SimpleOp);
     else
       Operands.push_back(Op);
@@ -1498,7 +1527,7 @@ bool CallAnalyzer::visitAlloca(AllocaInst &I) {
   // Check whether inlining will turn a dynamic alloca into a static
   // alloca and handle that case.
   if (I.isArrayAllocation()) {
-    Constant *Size = SimplifiedValues.lookup(I.getArraySize());
+    Constant *Size = getSimplifiedValue<Constant>(I.getArraySize());
     if (auto *AllocSize = dyn_cast_or_null<ConstantInt>(Size)) {
       // Sometimes a dynamic alloca could be converted into a static alloca
       // after this constant prop, and become a huge static alloca on an
@@ -2388,7 +2417,7 @@ bool CallAnalyzer::visitCallBase(CallBase &Call) {
     // Check if this happens to be an indirect function call to a known function
     // in this inline context. If not, we've done all we can.
     Value *Callee = Call.getCalledOperand();
-    F = dyn_cast_or_null<Function>(SimplifiedValues.lookup(Callee));
+    F = getSimplifiedValue<Function>(Callee);
     if (!F || F->getFunctionType() != Call.getFunctionType()) {
       onCallArgumentSetup(Call);
 
@@ -2483,8 +2512,7 @@ bool CallAnalyzer::visitSelectInst(SelectInst &SI) {
 
   Constant *TrueC = getDirectOrSimplifiedValue<Constant>(TrueVal);
   Constant *FalseC = getDirectOrSimplifiedValue<Constant>(FalseVal);
-  Constant *CondC =
-      dyn_cast_or_null<Constant>(SimplifiedValues.lookup(SI.getCondition()));
+  Constant *CondC = getSimplifiedValue<Constant>(SI.getCondition());
 
   if (!CondC) {
     // Select C, X, X => X
@@ -2833,8 +2861,9 @@ InlineResult CallAnalyzer::analyze() {
   auto CAI = CandidateCall.arg_begin();
   for (Argument &FAI : F.args()) {
     assert(CAI != CandidateCall.arg_end());
-    if (Constant *C = dyn_cast<Constant>(CAI))
-      SimplifiedValues[&FAI] = C;
+    SimplifiedValues[&FAI] = *CAI;
+    if (isa<Constant>(*CAI))
+      ++NumConstantArgs;
 
     Value *PtrArg = *CAI;
     if (ConstantInt *C = stripAndComputeInBoundsConstantOffsets(PtrArg)) {
@@ -2849,7 +2878,6 @@ InlineResult CallAnalyzer::analyze() {
     }
     ++CAI;
   }
-  NumConstantArgs = SimplifiedValues.size();
   NumConstantOffsetPtrArgs = ConstantOffsetPtrs.size();
   NumAllocaArgs = SROAArgValues.size();
 
@@ -2911,8 +2939,7 @@ InlineResult CallAnalyzer::analyze() {
     if (BranchInst *BI = dyn_cast<BranchInst>(TI)) {
       if (BI->isConditional()) {
         Value *Cond = BI->getCondition();
-        if (ConstantInt *SimpleCond =
-                dyn_cast_or_null<ConstantInt>(SimplifiedValues.lookup(Cond))) {
+        if (ConstantInt *SimpleCond = getSimplifiedValue<ConstantInt>(Cond)) {
           BasicBlock *NextBB = BI->getSuccessor(SimpleCond->isZero() ? 1 : 0);
           BBWorklist.insert(NextBB);
           KnownSuccessors[BB] = NextBB;
@@ -2922,8 +2949,7 @@ InlineResult CallAnalyzer::analyze() {
       }
     } else if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
       Value *Cond = SI->getCondition();
-      if (ConstantInt *SimpleCond =
-              dyn_cast_or_null<ConstantInt>(SimplifiedValues.lookup(Cond))) {
+      if (ConstantInt *SimpleCond = getSimplifiedValue<ConstantInt>(Cond)) {
         BasicBlock *NextBB = SI->findCaseValue(SimpleCond)->getCaseSuccessor();
         BBWorklist.insert(NextBB);
         KnownSuccessors[BB] = NextBB;

[nikic]

LGTM

[fhahn]

Is this NFC? Or could you add a test?

[tobias-stadler]

Is this NFC? Or could you add a test?

Yes, this should be NFC until we start using getSimplifiedValueUnchecked or start mapping Instructions to non-Constant.

[fhahn]

LGTM, thanks