[clang] Fix codegen of consteval functions returning an empty class, and related issues (PR #93115)

[Richard Smith via cfe-commits]

================
@@ -1336,75 +1336,56 @@ static llvm::Value *CreateCoercedLoad(Address Src, llvm::Type *Ty,
   return CGF.Builder.CreateLoad(Tmp);
 }
 
-// Function to store a first-class aggregate into memory.  We prefer to
-// store the elements rather than the aggregate to be more friendly to
-// fast-isel.
-// FIXME: Do we need to recurse here?
-void CodeGenFunction::EmitAggregateStore(llvm::Value *Val, Address Dest,
-                                         bool DestIsVolatile) {
-  // Prefer scalar stores to first-class aggregate stores.
-  if (llvm::StructType *STy = dyn_cast<llvm::StructType>(Val->getType())) {
-    for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i) {
-      Address EltPtr = Builder.CreateStructGEP(Dest, i);
-      llvm::Value *Elt = Builder.CreateExtractValue(Val, i);
-      Builder.CreateStore(Elt, EltPtr, DestIsVolatile);
-    }
-  } else {
-    Builder.CreateStore(Val, Dest, DestIsVolatile);
-  }
-}
-
 /// CreateCoercedStore - Create a store to \arg DstPtr from \arg Src,
 /// where the source and destination may have different types.  The
 /// destination is known to be aligned to \arg DstAlign bytes.
 ///
 /// This safely handles the case when the src type is larger than the
 /// destination type; the upper bits of the src will be lost.
-static void CreateCoercedStore(llvm::Value *Src,
-                               Address Dst,
-                               bool DstIsVolatile,
-                               CodeGenFunction &CGF) {
-  llvm::Type *SrcTy = Src->getType();
-  llvm::Type *DstTy = Dst.getElementType();
-  if (SrcTy == DstTy) {
-    CGF.Builder.CreateStore(Src, Dst, DstIsVolatile);
-    return;
-  }
-
-  llvm::TypeSize SrcSize = CGF.CGM.getDataLayout().getTypeAllocSize(SrcTy);
-
-  if (llvm::StructType *DstSTy = dyn_cast<llvm::StructType>(DstTy)) {
-    Dst = EnterStructPointerForCoercedAccess(Dst, DstSTy,
-                                             SrcSize.getFixedValue(), CGF);
-    DstTy = Dst.getElementType();
-  }
-
-  llvm::PointerType *SrcPtrTy = llvm::dyn_cast<llvm::PointerType>(SrcTy);
-  llvm::PointerType *DstPtrTy = llvm::dyn_cast<llvm::PointerType>(DstTy);
-  if (SrcPtrTy && DstPtrTy &&
-      SrcPtrTy->getAddressSpace() != DstPtrTy->getAddressSpace()) {
-    Src = CGF.Builder.CreateAddrSpaceCast(Src, DstTy);
-    CGF.Builder.CreateStore(Src, Dst, DstIsVolatile);
+void CodeGenFunction::CreateCoercedStore(llvm::Value *Src, Address Dst,
+                                         llvm::TypeSize DstSize,
+                                         bool DstIsVolatile) {
+  if (!DstSize)
     return;
-  }
 
-  // If the source and destination are integer or pointer types, just do an
-  // extension or truncation to the desired type.
-  if ((isa<llvm::IntegerType>(SrcTy) || isa<llvm::PointerType>(SrcTy)) &&
-      (isa<llvm::IntegerType>(DstTy) || isa<llvm::PointerType>(DstTy))) {
-    Src = CoerceIntOrPtrToIntOrPtr(Src, DstTy, CGF);
-    CGF.Builder.CreateStore(Src, Dst, DstIsVolatile);
-    return;
+  llvm::Type *SrcTy = Src->getType();
+  llvm::TypeSize SrcSize = CGM.getDataLayout().getTypeAllocSize(SrcTy);
+
+  // GEP into structs to try to make types match.
+  // FIXME: This isn't really that useful with opaque types, but it impacts a
+  // lot of regression tests.
+  if (SrcTy != Dst.getElementType()) {
+    if (llvm::StructType *DstSTy =
+            dyn_cast<llvm::StructType>(Dst.getElementType())) {
+      assert(!SrcSize.isScalable());
+      Dst = EnterStructPointerForCoercedAccess(Dst, DstSTy,
+                                               SrcSize.getFixedValue(), *this);
+    }
   }
 
-  llvm::TypeSize DstSize = CGF.CGM.getDataLayout().getTypeAllocSize(DstTy);
-
-  // If store is legal, just bitcast the src pointer.
-  if (isa<llvm::ScalableVectorType>(SrcTy) ||
-      isa<llvm::ScalableVectorType>(DstTy) ||
-      SrcSize.getFixedValue() <= DstSize.getFixedValue()) {
-    Dst = Dst.withElementType(SrcTy);
-    CGF.EmitAggregateStore(Src, Dst, DstIsVolatile);
+  if (SrcSize.isScalable() || SrcSize <= DstSize) {
+    if (SrcTy->isIntegerTy() && Dst.getElementType()->isPointerTy() &&
+        SrcSize == CGM.getDataLayout().getTypeAllocSize(Dst.getElementType())) {
+      // If the value is supposed to be a pointer, convert it before storing it.
+      Src = CoerceIntOrPtrToIntOrPtr(Src, Dst.getElementType(), *this);
----------------
zygoloid wrote:

It looks like we used to create either an `inttoptr` or `ptrtoint` here and now we only handle the `inttoptr` case. Is that OK?

https://github.com/llvm/llvm-project/pull/93115