[llvm-branch-commits] MC: Refactor FT_Align fragments when linker relaxation is enabled (PR #149465)

[Fangrui Song via llvm-branch-commits]

================
@@ -992,7 +965,30 @@ void MCAssembler::layoutSection(MCSection &Sec) {
   uint64_t Offset = 0;
   for (MCFragment &F : Sec) {
     F.Offset = Offset;
-    Offset += computeFragmentSize(F);
+    if (F.getKind() == MCFragment::FT_Align) {
+      Offset += F.getFixedSize();
+      unsigned Size = offsetToAlignment(Offset, F.getAlignment());
+      // In the nops mode, RISC-V style linker relaxation might adjust the size
+      // and add a fixup, even if `Size` is originally 0.
+      bool AlignFixup = false;
+      if (F.hasAlignEmitNops()) {
+        AlignFixup = getBackend().relaxAlign(F, Size);
+        // If the backend does not handle the fragment specially, pad with nops,
+        // but ensure that the padding is larger than the minimum nop size.
+        if (!AlignFixup)
+          while (Size % getBackend().getMinimumNopSize())
+            Size += F.getAlignment().value();
+      }
+      if (!AlignFixup && Size > F.getAlignMaxBytesToEmit())
+        Size = 0;
+      // Update the variable tail size. The content is ignored.
+      F.VarContentEnd = F.VarContentStart + Size;
----------------
MaskRay wrote:

Agree! Let me try `assert(F.VarContentStart == 0);`

https://github.com/llvm/llvm-project/pull/149465