[lld] [lld][LoongArch] GOT indirection to PC relative optimization (PR #123743)

[Zhaoxin Yang via llvm-commits]

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@@ -1152,6 +1154,58 @@ void LoongArch::tlsdescToLe(uint8_t *loc, const Relocation &rel,
   }
 }
 
+// Try GOT indirection to PC relative optimization when relaxation is enabled.
+// From:
+//  * pcalau12i $a0, %got_pc_hi20(sym_got)
+//  * ld.w/d    $a0, $a0, %got_pc_lo12(sym_got)
+// To:
+//  * pcalau12i $a0, %pc_hi20(sym)
+//  * addi.w/d  $a0, $a0, %pc_lo12(sym)
+//
+// Note: Althouth the optimization has been performed, the GOT entries still
+// exists, similarly to AArch64. Eliminating the entries will increase code
+// complexity.
+bool LoongArch::tryGotToPCRel(uint8_t *loc, const Relocation &rHi20,
+                              const Relocation &rLo12, uint64_t secAddr) const {
+  if (!rHi20.sym->isDefined() || rHi20.sym->isPreemptible ||
+      rHi20.sym->isGnuIFunc() ||
+      (ctx.arg.isPic && !cast<Defined>(*rHi20.sym).section))
+    return false;
+
+  Symbol &sym = *rHi20.sym;
+  uint64_t symLocal = sym.getVA(ctx) + rHi20.addend;
+  // Check if the address difference is within +/-2GB range.
+  // For simplicity, the range mentioned here is an approximate estimate and is
+  // not fully equivalent to the entire region that PC-relative addressing can
+  // cover.
+  int64_t pageOffset =
+      getLoongArchPage(symLocal) - getLoongArchPage(secAddr + rHi20.offset);
+  if (!isInt<20>(pageOffset >> 12))
+    return false;
+
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ylzsx wrote:

Thanks, I will fix them.

https://github.com/llvm/llvm-project/pull/123743