[llvm] [WIP] Extend data layout to add sentinel pointer value for address space. (PR #83109)

[Matt Arsenault via llvm-commits]

================
@@ -502,6 +520,33 @@ Error DataLayout::parseSpecifier(StringRef Desc) {
         return Err;
       break;
     }
+    case 'z': {
+      sentinelValueDefined = true;
+      unsigned AddrSpace = 0;
+      int64_t Value;
+      // for unlisted address spaces e.g., z:0
+      if (Tok.empty()) {
+        if (Error Err = getIntForAddrSpace(Rest, Value))
+          return Err;
+        setSentinelPointerValue(INT_MAX, Value);
+        break;
+      } else {
+        if (Error Err = getInt(Tok, AddrSpace))
+          return Err;
+        if (!isUInt<24>(AddrSpace))
+          return reportError("Invalid address space, must be a 24-bit integer");
+      }
+      if (Rest.empty())
+        return reportError(
+            "Missing address space value specification for pointer in "
----------------
arsenm wrote:

error messages should start with lowercase

https://github.com/llvm/llvm-project/pull/83109