[clang] [llvm] [Hexagon] Fix unusable SCS reg, make it selectable (PR #213820)

[Santanu Das via llvm-commits]

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@@ -163,6 +163,38 @@ static std::string describeSanitizeArg(const llvm::opt::Arg *A,
 /// Sanitizers set.
 static std::string toString(const clang::SanitizerSet &Sanitizers);
 
+/// Map a Hexagon callee-saved register number (16-27) to its -ffixed-rN
+/// option, used to check that the shadow call stack pointer is reserved.
+static options::ID getHexagonFixedRegOption(unsigned RegNo) {
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quic-santdas wrote:

Since the registers are contiguous, we can probably have a range check like this:

if (RegNo >= 16 && RegNo <= 27)
  return  options::OPT_ffixed_r16 + (RegNo - 16));


https://github.com/llvm/llvm-project/pull/213820