[clang] [lld] [llvm] CodeGen: Emit .prefalign directives based on the prefalign attribute. (PR #155529)

[Fangrui Song via llvm-commits]

================
@@ -999,8 +999,20 @@ void AsmPrinter::emitFunctionHeader() {
     emitVisibility(CurrentFnSym, F.getVisibility());
 
   emitLinkage(&F, CurrentFnSym);
-  if (MAI->hasFunctionAlignment())
-    emitAlignment(MF->getPreferredAlignment(), &F);
+  if (MAI->hasFunctionAlignment()) {
+    // The preferred alignment directive will not have the intended effect
+    // unless function sections are enabled.
+    if (MAI->useIntegratedAssembler() && MAI->hasPreferredAlignment() &&
+        TM.getFunctionSections()) {
----------------
MaskRay wrote:

There is another issue, redundant `.prefalign`. Fix: https://github.com/llvm/llvm-project/pull/191675

https://github.com/llvm/llvm-project/pull/155529