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

[Zhaoxin Yang via llvm-commits]

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@@ -1155,6 +1157,78 @@ void LoongArch::tlsdescToLe(uint8_t *loc, const Relocation &rel,
   }
 }
 
+// Try GOT indirection to PC relative optimization.
+// 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 {
+  // Check if the relocations apply to consecutive instructions.
+  if (rHi20.offset + 4 != rLo12.offset)
+    return false;
+
+  // Check if the relocations reference the same symbol and skip undefined,
+  // preemptible and STT_GNU_IFUNC symbols.
+  if (!rHi20.sym || rHi20.sym != rLo12.sym || !rHi20.sym->isDefined() ||
+      rHi20.sym->isPreemptible || rHi20.sym->isGnuIFunc())
+    return false;
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ylzsx wrote:

I have added this test in a previous patch. See `loongarch-relax-pc-hi20-lo12-got-symbols.s`.

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