Add shouldDecomposeStructAllocas to TargetTransformInfo

Author: Icohedron

llvm/include/llvm/Analysis/TargetTransformInfo.h

@@ -1977,6 +1977,11 @@ class TargetTransformInfo {
   /// target.
   LLVM_ABI bool allowVectorElementIndexingUsingGEP() const;
 
+  /// \returns True if the target does not support struct allocas and therefore
+  /// requires struct alloca instructions to be scalarized / decomposed into
+  /// its components.
+  LLVM_ABI bool shouldDecomposeStructAllocas() const;
+
 private:
   std::unique_ptr<const TargetTransformInfoImplBase> TTIImpl;
 };

llvm/include/llvm/Analysis/TargetTransformInfoImpl.h

@@ -1163,6 +1163,8 @@ class TargetTransformInfoImplBase {
 
   virtual bool allowVectorElementIndexingUsingGEP() const { return true; }
 
+  virtual bool shouldDecomposeStructAllocas() const { return false; }
+
 protected:
   // Obtain the minimum required size to hold the value (without the sign)
   // In case of a vector it returns the min required size for one element.

llvm/lib/Analysis/TargetTransformInfo.cpp

@@ -1506,6 +1506,10 @@ bool TargetTransformInfo::allowVectorElementIndexingUsingGEP() const {
   return TTIImpl->allowVectorElementIndexingUsingGEP();
 }
 
+bool TargetTransformInfo::shouldDecomposeStructAllocas() const {
+  return TTIImpl->shouldDecomposeStructAllocas();
+}
+
 TargetTransformInfoImplBase::~TargetTransformInfoImplBase() = default;
 
 TargetIRAnalysis::TargetIRAnalysis() : TTICallback(&getDefaultTTI) {}

llvm/lib/Target/DirectX/DirectXTargetTransformInfo.cpp

@@ -65,3 +65,7 @@ bool DirectXTTIImpl::isTargetIntrinsicTriviallyScalarizable(
     return false;
   }
 }
+
+bool DirectXTTIImpl::shouldDecomposeStructAllocas() const {
+  return true;
+}

llvm/lib/Target/DirectX/DirectXTargetTransformInfo.h

@@ -39,6 +39,7 @@ class DirectXTTIImpl final : public BasicTTIImplBase<DirectXTTIImpl> {
                                           unsigned ScalarOpdIdx) const override;
   bool isTargetIntrinsicWithOverloadTypeAtArg(Intrinsic::ID ID,
                                               int OpdIdx) const override;
+  bool shouldDecomposeStructAllocas() const override;
 };
 } // namespace llvm