Add earlier check for invalid SV_Target[n] (#6771)

According to the HLSL semantics documentation, the valid semantic
indices for SV_Target[n] are 0 <= n <= 7:

https://learn.microsoft.com/en-us/windows/win32/direct3dhlsl/dx-graphics-hlsl-semantics

A check for this already exists in DXIL validation, but for large values
of n, crashes and/or buffer overruns may occur during compilation before
validation, so an earlier check is needed.

Fixes #6115

tools/clang/include/clang/Basic/DiagnosticSemaKinds.td

@@ -7962,6 +7962,8 @@ def warn_hlsl_barrier_no_mem_with_required_device_scope: Warning<
 def warn_hlsl_legacy_integer_literal_signedness: Warning<
   "literal value is treated as signed in HLSL 2021 and earlier, and unsigned in later language versions">,
   InGroup<HLSLLegacyLiterals>, DefaultIgnore;
+def err_hlsl_unsupported_semantic_index: Error<
+  "'%0' is defined with semantic index %1, but only values 0 through %2 are supported">;
 // HLSL Change Ends
 
 // SPIRV Change Starts

tools/clang/include/clang/Sema/Sema.h

@@ -9108,6 +9108,8 @@ class Sema {
                                 bool isImplicit);
   QualType getHLSLDefaultSpecialization(TemplateDecl *Decl);
   // HLSL Change End - adjust this from T* to T&-like
+
+  void DiagnoseSemanticDecl(hlsl::SemanticDecl *Decl); // HLSL Change
 };
 
 /// \brief RAII object that enters a new expression evaluation context.

tools/clang/lib/Parse/ParseDecl.cpp

@@ -630,6 +630,7 @@ bool Parser::MaybeParseHLSLAttributes(std::vector<hlsl::UnusualAnnotation *> &ta
       }
       hlsl::SemanticDecl *pUA = new (context) hlsl::SemanticDecl(semanticName);
       pUA->Loc = Tok.getLocation();
+      Actions.DiagnoseSemanticDecl(pUA);
       ConsumeToken(); // consume semantic
 
       target.push_back(pUA);

tools/clang/lib/Sema/SemaDecl.cpp

@@ -11,8 +11,8 @@
 //
 //===----------------------------------------------------------------------===//
 
-#include "clang/Sema/SemaInternal.h"
 #include "TypeLocBuilder.h"
+#include "dxc/DXIL/DxilSemantic.h" // HLSL Change
 #include "clang/AST/ASTConsumer.h"
 #include "clang/AST/ASTContext.h"
 #include "clang/AST/ASTLambda.h"
@@ -42,13 +42,14 @@
 #include "clang/Sema/ParsedTemplate.h"
 #include "clang/Sema/Scope.h"
 #include "clang/Sema/ScopeInfo.h"
+#include "clang/Sema/SemaHLSL.h" // HLSL Change
+#include "clang/Sema/SemaInternal.h"
 #include "clang/Sema/Template.h"
 #include "llvm/ADT/SmallString.h"
 #include "llvm/ADT/Triple.h"
 #include <algorithm>
 #include <cstring>
 #include <functional>
-#include "clang/Sema/SemaHLSL.h" // HLSL Change
 using namespace clang;
 using namespace sema;
 
@@ -14629,3 +14630,20 @@ AvailabilityResult Sema::getCurContextAvailability() const {
   return D ? D->getAvailability() : AR_Available;
 }
 
+// HLSL Change Begin
+void Sema::DiagnoseSemanticDecl(hlsl::SemanticDecl *Decl) {
+  StringRef SemName = Decl->SemanticName;
+
+  StringRef BaseSemName; // The 'FOO' in 'FOO1'
+  uint32_t SemIndex;     // The '1' in 'FOO1'
+
+  // Split name and index.
+  hlsl::Semantic::DecomposeNameAndIndex(SemName, &BaseSemName, &SemIndex);
+
+  // The valid semantic indices for SV_Target[n] are 0 <= n <= 7.
+  if (BaseSemName.equals("SV_Target") && SemIndex > 7) {
+    Diag(Decl->Loc, diag::err_hlsl_unsupported_semantic_index)
+        << SemName << SemIndex << "7";
+  }
+}
+// HLSL Change Ends

tools/clang/test/SemaHLSL/hlsl/semantics/sv_target.index.hlsl

@@ -0,0 +1,10 @@
+// RUN: %dxc -T ps_6_0 -E zero -verify %s
+// RUN: %dxc -T ps_6_0 -E seven -verify %s
+
+float4 zero() : SV_Target0 { /* expected-no-diagnostics */
+    return float4(0, 1, 2, 3);
+}
+
+float4 seven() : SV_Target7 { /* expected-no-diagnostics */
+    return float4(0, 1, 2, 3);
+}

tools/clang/test/SemaHLSL/hlsl/semantics/sv_target.index.invalid.hlsl

@@ -0,0 +1,5 @@
+// RUN: %dxc -T ps_6_0 -verify %s
+
+float4 bad() : SV_Target8 { /* expected-error{{'SV_Target8' is defined with semantic index 8, but only values 0 through 7 are supported}} */
+    return float4(0, 1, 2, 3);
+}

tools/clang/test/SemaHLSL/hlsl/semantics/sv_target.index.struct.invalid.hlsl

@@ -0,0 +1,9 @@
+// RUN: %dxc -T ps_6_0 -verify %s
+
+struct S {
+  float4 t : SV_Target12345; /* expected-error{{'SV_Target12345' is defined with semantic index 12345, but only values 0 through 7 are supported}} */
+};
+
+S main() {
+    return S(float4(0, 1, 2, 3));
+}