NFC: deduplicate isRepeatedBytePattern from clang to LLVM's isBytewiseValue

[jfb]

Summary

This code was in CGDecl.cpp and really belongs in LLVM. It happened to have isBytewiseValue which served a very similar purpose but wasn't as powerful as clang's version. Remove the clang version, and augment isBytewiseValue to be as powerful so that clang does the same thing it used to.

LLVM part of this patch: D51751

[MatzeB]

• I'm not a good person to review clang changes.
• I assume the review lacks the changes on the llvm side?
• On the LLVM side this feels like something for Analysis/ValueTracking.h in fact I already see Value *isBytewiseValue(Value *V); there, maybe that is good enough for your purpose?

[jfb]

In D51752#1226462, @MatzeB wrote:

• I'm not a good person to review clang changes.
• I assume the review lacks the changes on the llvm side?
• On the LLVM side this feels like something for Analysis/ValueTracking.h in fact I already see Value *isBytewiseValue(Value *V); there, maybe that is good enough for your purpose?

Indeed, I just noticed the same. I'll try to figure out why it isn't firing where I want it to.

[jfb]

In D51752#1226465, @jfb wrote:

In D51752#1226462, @MatzeB wrote:

• I'm not a good person to review clang changes.
• I assume the review lacks the changes on the llvm side?
• On the LLVM side this feels like something for Analysis/ValueTracking.h in fact I already see Value *isBytewiseValue(Value *V); there, maybe that is good enough for your purpose?

Indeed, I just noticed the same. I'll try to figure out why it isn't firing where I want it to.

I think I'll just improve isBytewiseValue to do all the things isRepeatedBytePattern does. I'll update this patch to still delete constantIsRepeatedBytePattern, but use the new and improved isBytewiseValue.

[MatzeB]

In D51752#1226462, @MatzeB wrote:

• I assume the review lacks the changes on the llvm side?

Oops missed the link to the llvm changes in the description... At least in theory you should be able to make a review over all changes in parallel by using subversion or the experimental llvm git monorepo with llvm/utils/git-svn/git-llvm (admittedly haven't tried it myself yet either).

[jfb]

In D51752#1226474, @MatzeB wrote:

In D51752#1226462, @MatzeB wrote:

• I assume the review lacks the changes on the llvm side?

Oops missed the link to the llvm changes in the description... At least in theory you should be able to make a review over all changes in parallel by using subversion or the experimental llvm git monorepo with llvm/utils/git-svn/git-llvm (admittedly haven't tried it myself yet either).

Haha yeah I'm still using my now years-old workflow. Haven't tried the new fancy ones yet, waiting for the actual move to do so :)

[jfb]

• Use isBytewiseValue instead.

[MatzeB]

Looks obvious and LGTM.

[jfb]

Will wait on D51751 before committing, otherwise clang tests will start failing (because current isRepeatedBytePattern isn't capable enough).

lib/CodeGen/CGDecl.cpp

 #include "clang/AST/CharUnits.h"
 #include "clang/AST/Decl.h"
 #include "clang/AST/DeclObjC.h"
 #include "clang/AST/DeclOpenMP.h"
 #include "clang/Basic/SourceManager.h"
 #include "clang/Basic/TargetInfo.h"
 #include "clang/CodeGen/CGFunctionInfo.h"
 #include "clang/Frontend/CodeGenOptions.h"
+#include "llvm/Analysis/ValueTracking.h"
 #include "llvm/IR/DataLayout.h"
 #include "llvm/IR/GlobalVariable.h"
 #include "llvm/IR/Intrinsics.h"
 #include "llvm/IR/Type.h"
 
 using namespace clang;
 using namespace CodeGen;
 
static bool shouldUseBZeroPlusStoresToInitialize(llvm::Constant *Init,
   // plopping in more stores.
   unsigned StoreBudget = 6;
   uint64_t SizeLimit = 32;
 
   return GlobalSize > SizeLimit &&
          canEmitInitWithFewStoresAfterBZero(Init, StoreBudget);
 }
 
-/// A byte pattern.
-///
-/// Can be "any" pattern if the value was padding or known to be undef.
-/// Can be "none" pattern if a sequence doesn't exist.
-class BytePattern {
-  uint8_t Val;
-  enum class ValueType : uint8_t { Specific, Any, None } Type;
-  BytePattern(ValueType Type) : Type(Type) {}
-
-public:
-  BytePattern(uint8_t Value) : Val(Value), Type(ValueType::Specific) {}
-  static BytePattern Any() { return BytePattern(ValueType::Any); }
-  static BytePattern None() { return BytePattern(ValueType::None); }
-  bool isAny() const { return Type == ValueType::Any; }
-  bool isNone() const { return Type == ValueType::None; }
-  bool isValued() const { return Type == ValueType::Specific; }
-  uint8_t getValue() const {
-    assert(isValued());
-    return Val;
-  }
-  BytePattern merge(const BytePattern Other) const {
-    if (isNone() || Other.isNone())
-      return None();
-    if (isAny())
-      return Other;
-    if (Other.isAny())
-      return *this;
-    if (getValue() == Other.getValue())
-      return *this;
-    return None();
-  }
-};
-
-/// Figures out whether the constant can be initialized with memset.
-static BytePattern constantIsRepeatedBytePattern(llvm::Constant *C) {
-  if (isa<llvm::ConstantAggregateZero>(C) || isa<llvm::ConstantPointerNull>(C))
-    return BytePattern(0x00);
-  if (isa<llvm::UndefValue>(C))
-    return BytePattern::Any();
-
-  if (isa<llvm::ConstantInt>(C)) {
-    auto *Int = cast<llvm::ConstantInt>(C);
-    if (Int->getBitWidth() % 8 != 0)
-      return BytePattern::None();
-    const llvm::APInt &Value = Int->getValue();
-    if (Value.isSplat(8))
-      return BytePattern(Value.getLoBits(8).getLimitedValue());
-    return BytePattern::None();
-  }
-
-  if (isa<llvm::ConstantFP>(C)) {
-    auto *FP = cast<llvm::ConstantFP>(C);
-    llvm::APInt Bits = FP->getValueAPF().bitcastToAPInt();
-    if (Bits.getBitWidth() % 8 != 0)
-      return BytePattern::None();
-    if (!Bits.isSplat(8))
-      return BytePattern::None();
-    return BytePattern(Bits.getLimitedValue() & 0xFF);
-  }
-
-  if (isa<llvm::ConstantVector>(C)) {
-    llvm::Constant *Splat = cast<llvm::ConstantVector>(C)->getSplatValue();
-    if (Splat)
-      return constantIsRepeatedBytePattern(Splat);
-    return BytePattern::None();
-  }
-
-  if (isa<llvm::ConstantArray>(C) || isa<llvm::ConstantStruct>(C)) {
-    BytePattern Pattern(BytePattern::Any());
-    for (unsigned I = 0, E = C->getNumOperands(); I != E; ++I) {
-      llvm::Constant *Elt = cast<llvm::Constant>(C->getOperand(I));
-      Pattern = Pattern.merge(constantIsRepeatedBytePattern(Elt));
-      if (Pattern.isNone())
-        return Pattern;
-    }
-    return Pattern;
-  }
-
-  if (llvm::ConstantDataSequential *CDS =
-          dyn_cast<llvm::ConstantDataSequential>(C)) {
-    BytePattern Pattern(BytePattern::Any());
-    for (unsigned I = 0, E = CDS->getNumElements(); I != E; ++I) {
-      llvm::Constant *Elt = CDS->getElementAsConstant(I);
-      Pattern = Pattern.merge(constantIsRepeatedBytePattern(Elt));
-      if (Pattern.isNone())
-        return Pattern;
-    }
-    return Pattern;
-  }
-
-  // BlockAddress, ConstantExpr, and everything else is scary.
-  return BytePattern::None();
-}
-
 /// Decide whether we should use memset to initialize a local variable instead
 /// of using a memcpy from a constant global. Assumes we've already decided to
 /// not user bzero.
 /// FIXME We could be more clever, as we are for bzero above, and generate
 ///       memset followed by stores. It's unclear that's worth the effort.
-static BytePattern shouldUseMemSetToInitialize(llvm::Constant *Init,
+static llvm::Value *shouldUseMemSetToInitialize(llvm::Constant *Init,
                                                 uint64_t GlobalSize) {
   uint64_t SizeLimit = 32;
   if (GlobalSize <= SizeLimit)
-    return BytePattern::None();
-  return constantIsRepeatedBytePattern(Init);
+    return nullptr;
+  return llvm::isBytewiseValue(Init);
 }
 
 static void emitStoresForConstant(CodeGenModule &CGM, const VarDecl &D,
                                   Address Loc, bool isVolatile,
                                   CGBuilderTy &Builder,
                                   llvm::Constant *constant) {
   auto *Int8Ty = llvm::IntegerType::getInt8Ty(CGM.getLLVMContext());
   auto *IntPtrTy = CGM.getDataLayout().getIntPtrType(CGM.getLLVMContext());
if (shouldUseBZeroPlusStoresToInitialize(constant, ConstantSize)) {
     if (!valueAlreadyCorrect) {
       Loc = Builder.CreateBitCast(
           Loc, constant->getType()->getPointerTo(Loc.getAddressSpace()));
       emitStoresForInitAfterBZero(CGM, constant, Loc, isVolatile, Builder);
     }
     return;
   }
 
-  BytePattern Pattern = shouldUseMemSetToInitialize(constant, ConstantSize);
-  if (!Pattern.isNone()) {
-    uint8_t Value = Pattern.isAny() ? 0x00 : Pattern.getValue();
+  llvm::Value *Pattern = shouldUseMemSetToInitialize(constant, ConstantSize);
+  if (Pattern) {
+    uint64_t Value = 0x00;
+    if (!isa<llvm::UndefValue>(Pattern)) {
+      const llvm::APInt &AP = cast<llvm::ConstantInt>(Pattern)->getValue();
+      assert(AP.getBitWidth() <= 8);
+      Value = AP.getLimitedValue();
+    }
     Builder.CreateMemSet(Loc, llvm::ConstantInt::get(Int8Ty, Value), SizeVal,
                          isVolatile);
     return;
   }
 
   // Otherwise, create a temporary global with the initializer then memcpy from
   // the global to the alloca.
   std::string Name = getStaticDeclName(CGM, D);