[llvm] [clang] [AIX][TLS] Disallow the use of -maix-small-local-exec-tls and -fno-data-sections (PR #79252)

[Amy Kwan via cfe-commits]

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@@ -124,10 +124,23 @@ void PPCSubtarget::initSubtargetFeatures(StringRef CPU, StringRef TuneCPU,
   // Determine endianness.
   IsLittleEndian = TM.isLittleEndian();
 
-  if (HasAIXSmallLocalExecTLS && (!TargetTriple.isOSAIX() || !IsPPC64))
-    report_fatal_error(
-      "The aix-small-local-exec-tls attribute is only supported on AIX in "
-      "64-bit mode.\n", false);
+  if (HasAIXSmallLocalExecTLS) {
+    if (!TargetTriple.isOSAIX() || !IsPPC64)
+      report_fatal_error(
+          "The aix-small-local-exec-tls attribute is only supported on AIX in "
+          "64-bit mode.\n",
+          false);
+    // The aix-small-local-exec-tls attribute should only be used with
+    // -data-sections, as having data sections turned off with this option
+    // is not ideal for performance. Moreover, the small-local-exec-tls region
+    // is a limited resource, and should not be used for variables that may
+    // be replaced.
+    if (!TM.getDataSections())
+      report_fatal_error(
+          "The aix-small-local-exec-tls attribute can only be specified with "
+          "-data-sections.\n",
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amy-kwan wrote:

I kept the llvm portion as `-data-sections` since the option for llc is `-data-sections` rather than `-fdata-sections` (which is the option for clang).

https://github.com/llvm/llvm-project/pull/79252