[clang] [llvm] [HLSL] Implement explicit layout for default constant buffer ($Globals) (PR #128991)

[Alex Sepkowski via cfe-commits]

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@@ -89,14 +99,57 @@ llvm::TargetExtType *HLSLBufferLayoutBuilder::createLayoutType(
     RecordTypes.pop_back();
 
     for (const auto *FD : RT->getDecl()->fields()) {
-      assert((!Packoffsets || Index < Packoffsets->size()) &&
-             "number of elements in layout struct does not "
-             "match number of packoffset annotations");
+      unsigned FieldOffset = UINT_MAX;
+      llvm::Type *FieldType = nullptr;
+
+      if (Packoffsets) {
+        // have packoffset/register(c#) annotations
+        assert(Index < Packoffsets->size() &&
+               "number of elements in layout struct does not match number of "
+               "packoffset annotations");
+        int PO = (*Packoffsets)[Index++];
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alsepkow wrote:

P0 should be a const, I think? I noticed we don't really use that pattern in DXC but it looks like it is used here.

https://github.com/llvm/llvm-project/pull/128991