Reapply "[DXIL][Analysis] Make alignment on StructuredBuffer optional" (#101113)

Unfortunately storing a `MaybeAlign` in ResourceInfo deletes our move
constructor in compilers that haven't implemented [P0602R4], like GCC 7.
Since we only ever use the alignment in ways where alignment 1 and unset
are ambiguous anyway, we'll just store the integer AlignLog2 value that
we'll eventually use directly.

[P0602R4]:
https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2018/p0602r4.html

This reverts commit c22171f, reapplying
a94edb6.

Author: bogner

llvm/include/llvm/Analysis/DXILResource.h

@@ -47,10 +47,14 @@ class ResourceInfo {
 
   struct StructInfo {
     uint32_t Stride;
-    Align Alignment;
+    // Note: we store an integer here rather than using `MaybeAlign` because in
+    // GCC 7 MaybeAlign isn't trivial so having one in this union would delete
+    // our move constructor.
+    // See https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2018/p0602r4.html
+    uint32_t AlignLog2;
 
     bool operator==(const StructInfo &RHS) const {
-      return std::tie(Stride, Alignment) == std::tie(RHS.Stride, RHS.Alignment);
+      return std::tie(Stride, AlignLog2) == std::tie(RHS.Stride, RHS.AlignLog2);
     }
     bool operator!=(const StructInfo &RHS) const { return !(*this == RHS); }
   };
@@ -138,10 +142,10 @@ class ResourceInfo {
     CBufferSize = Size;
   }
   void setSampler(dxil::SamplerType Ty) { SamplerTy = Ty; }
-  void setStruct(uint32_t Stride, Align Alignment) {
+  void setStruct(uint32_t Stride, MaybeAlign Alignment) {
     assert(isStruct() && "Not a Struct");
     Struct.Stride = Stride;
-    Struct.Alignment = Alignment;
+    Struct.AlignLog2 = Alignment ? Log2(*Alignment) : 0;
   }
   void setTyped(dxil::ElementType ElementTy, uint32_t ElementCount) {
     assert(isTyped() && "Not Typed");
@@ -164,7 +168,7 @@ class ResourceInfo {
                           dxil::ResourceKind Kind);
   static ResourceInfo RawBuffer(Value *Symbol, StringRef Name);
   static ResourceInfo StructuredBuffer(Value *Symbol, StringRef Name,
-                                       uint32_t Stride, Align Alignment);
+                                       uint32_t Stride, MaybeAlign Alignment);
   static ResourceInfo Texture2DMS(Value *Symbol, StringRef Name,
                                   dxil::ElementType ElementTy,
                                   uint32_t ElementCount, uint32_t SampleCount);
@@ -180,9 +184,9 @@ class ResourceInfo {
   static ResourceInfo RWRawBuffer(Value *Symbol, StringRef Name,
                                   bool GloballyCoherent, bool IsROV);
   static ResourceInfo RWStructuredBuffer(Value *Symbol, StringRef Name,
-                                         uint32_t Stride,
-                                         Align Alignment, bool GloballyCoherent,
-                                         bool IsROV, bool HasCounter);
+                                         uint32_t Stride, MaybeAlign Alignment,
+                                         bool GloballyCoherent, bool IsROV,
+                                         bool HasCounter);
   static ResourceInfo RWTexture2DMS(Value *Symbol, StringRef Name,
                                     dxil::ElementType ElementTy,
                                     uint32_t ElementCount, uint32_t SampleCount,

llvm/lib/Analysis/DXILResource.cpp

@@ -79,7 +79,8 @@ ResourceInfo ResourceInfo::RawBuffer(Value *Symbol, StringRef Name) {
 }
 
 ResourceInfo ResourceInfo::StructuredBuffer(Value *Symbol, StringRef Name,
-                                            uint32_t Stride, Align Alignment) {
+                                            uint32_t Stride,
+                                            MaybeAlign Alignment) {
   ResourceInfo RI(ResourceClass::SRV, ResourceKind::StructuredBuffer, Symbol,
                   Name);
   RI.setStruct(Stride, Alignment);
@@ -127,7 +128,8 @@ ResourceInfo ResourceInfo::RWRawBuffer(Value *Symbol, StringRef Name,
 }
 
 ResourceInfo ResourceInfo::RWStructuredBuffer(Value *Symbol, StringRef Name,
-                                              uint32_t Stride, Align Alignment,
+                                              uint32_t Stride,
+                                              MaybeAlign Alignment,
                                               bool GloballyCoherent, bool IsROV,
                                               bool HasCounter) {
   ResourceInfo RI(ResourceClass::UAV, ResourceKind::StructuredBuffer, Symbol,
@@ -284,7 +286,7 @@ MDTuple *ResourceInfo::getAsMetadata(LLVMContext &Ctx) const {
 
 std::pair<uint32_t, uint32_t> ResourceInfo::getAnnotateProps() const {
   uint32_t ResourceKind = llvm::to_underlying(Kind);
-  uint32_t AlignLog2 = isStruct() ? Log2(Struct.Alignment) : 0;
+  uint32_t AlignLog2 = isStruct() ? Struct.AlignLog2 : 0;
   bool IsUAV = isUAV();
   bool IsROV = IsUAV && UAVFlags.IsROV;
   bool IsGloballyCoherent = IsUAV && UAVFlags.GloballyCoherent;

llvm/unittests/Analysis/DXILResourceTest.cpp

@@ -151,6 +151,19 @@ TEST(DXILResource, AnnotationsAndMetadata) {
   EXPECT_MDEQ(
       MD, TestMD.get(0, Symbol, "Buffer0", 0, 0, 1, 12, 0, TestMD.get(1, 16)));
 
+  // StructuredBuffer<float3> Buffer1 : register(t1);
+  Symbol = UndefValue::get(StructType::create(
+      Context, {Floatx3Ty}, "class.StructuredBuffer<vector<float, 3> >"));
+  Resource = ResourceInfo::StructuredBuffer(Symbol, "Buffer1",
+                                            /*Stride=*/12, {});
+  Resource.bind(1, 0, 1, 1);
+  Props = Resource.getAnnotateProps();
+  EXPECT_EQ(Props.first, 0x0000000cU);
+  EXPECT_EQ(Props.second, 0x0000000cU);
+  MD = Resource.getAsMetadata(Context);
+  EXPECT_MDEQ(
+      MD, TestMD.get(1, Symbol, "Buffer1", 0, 1, 1, 12, 0, TestMD.get(1, 12)));
+
   // Texture2D<float4> ColorMapTexture : register(t2);
   Symbol = UndefValue::get(StructType::create(
       Context, {Floatx4Ty}, "class.Texture2D<vector<float, 4> >"));