[clang] [HLSL] add loop unroll (PR #93879)

[Farzon Lotfi via cfe-commits]

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@@ -635,6 +635,17 @@ void LoopInfoStack::push(BasicBlock *Header, clang::ASTContext &Ctx,
         Option = LoopHintAttr::UnrollCount;
         State = LoopHintAttr::Numeric;
       }
+    } else if (HLSLLoopHint) {
+      ValueInt = HLSLLoopHint->getDirective();
+      if (HLSLLoopHint->getSemanticSpelling() ==
+          HLSLLoopHintAttr::Spelling::Microsoft_unroll) {
+        if (ValueInt == 0)
+          State = LoopHintAttr::Enable;
+        if (ValueInt > 0) {
+          Option = LoopHintAttr::UnrollCount;
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farzonl wrote:

@dmpots you are correct. It's very likely we will pursue a breaking change based on the feedback I've been gathering throughout the day. Since HLSL202x  applies for both clang-dxc and an dxc It may be worth making a similar change in DXC to allow us to measure how much of a breaking change this would be via experiments before we come to a final decision.

https://github.com/llvm/llvm-project/pull/93879