[LoongArch] Use section-relaxable check instead of relax feature from STI (llvm#153792)

In some cases, such as using `lto` or `llc`, relax feature is not
available from this `SubtargetInfo` (`LoongArchAsmBackend` is
instantiated too early), causing loss of relocations.

This commit modifiy the condition to check whether the section which
contains the two symbols is relaxable. If not relaxable, no need to
record relocations.

Author: zhaoqi5

llvm/lib/Target/LoongArch/MCTargetDesc/LoongArchAsmBackend.cpp

@@ -439,10 +439,10 @@ bool LoongArchAsmBackend::addReloc(const MCFragment &F, const MCFixup &Fixup,
           isPCRelFixupResolved(Target.getSubSym(), F))
         return Fallback();
 
-      // In SecA == SecB case. If the linker relaxation is disabled, the
+      // In SecA == SecB case. If the section is not linker-relaxable, the
       // FixedValue has already been calculated out in evaluateFixup,
       // return true and avoid record relocations.
-      if (&SecA == &SecB && !STI.hasFeature(LoongArch::FeatureRelax))
+      if (&SecA == &SecB && !SecA.isLinkerRelaxable())
         return true;
     }
 

llvm/test/CodeGen/LoongArch/fix-addsub-relocs-with-relax.ll

@@ -1,13 +1,7 @@
 ; RUN: llc --filetype=obj --mtriple=loongarch64 %s -o %t.o
 ; RUN: llvm-readobj -r %t.o | FileCheck %s
 ; RUN: llc --filetype=obj --mtriple=loongarch64 --mattr=+relax %s -o %t.r
-; RUN: llvm-readobj -r %t.r | FileCheck --check-prefixes=CHECK,RELAX %s
-
-;; This test shows the loss of ADD/SUB relocations because relax feature
-;; is not available from SubtargetInfo (LoongArchAsmBackend is instantiated
-;; too early). ie. code generation takes the relax feature from attributes,
-;; but ADD/SUB relocations recording losses the relax feature.
-;; A later commit will fix it.
+; RUN: llvm-readobj -r %t.r | FileCheck %s
 
 ; CHECK:      Relocations [
 ; CHECK-NEXT:   Section ({{.*}}) .rela.text {
@@ -20,17 +14,17 @@
 ; CHECK-NEXT:     0x8 R_LARCH_32 .debug_abbrev 0x0
 ; CHECK-NEXT:     0x11 R_LARCH_32 .L0 0x0
 ; CHECK-NEXT:     0x15 R_LARCH_32 .Lline_table_start0 0x0
-; RELAX-NEXT:     0x1B R_LARCH_ADD32 .L0 0x0
-; RELAX-NEXT:     0x1B R_LARCH_SUB32 .L0 0x0
+; CHECK-NEXT:     0x1B R_LARCH_ADD32 .L0 0x0
+; CHECK-NEXT:     0x1B R_LARCH_SUB32 .L0 0x0
 ; CHECK-NEXT:     0x1F R_LARCH_32 .L0 0x0
-; RELAX-NEXT:     0x25 R_LARCH_ADD32 .L0 0x0
-; RELAX-NEXT:     0x25 R_LARCH_SUB32 .L0 0x0
+; CHECK-NEXT:     0x25 R_LARCH_ADD32 .L0 0x0
+; CHECK-NEXT:     0x25 R_LARCH_SUB32 .L0 0x0
 ; CHECK-NEXT:   }
 ; CHECK:        Section ({{.*}}) .rela.debug_frame {
 ; CHECK-NEXT:     0x1C R_LARCH_32 .L0 0x0
 ; CHECK-NEXT:     0x20 R_LARCH_64 .L0 0x0
-; RELAX-NEXT:     0x28 R_LARCH_ADD64 .L0 0x0
-; RELAX-NEXT:     0x28 R_LARCH_SUB64 .L0 0x0
+; CHECK-NEXT:     0x28 R_LARCH_ADD64 .L0 0x0
+; CHECK-NEXT:     0x28 R_LARCH_SUB64 .L0 0x0
 ; CHECK-NEXT:     0x3F R_LARCH_ADD6 .L0 0x0
 ; CHECK-NEXT:     0x3F R_LARCH_SUB6 .L0 0x0
 ; CHECK-NEXT:   }
@@ -39,8 +33,8 @@
 ; CHECK-NEXT:     0x31 R_LARCH_32 .debug_line_str 0x2
 ; CHECK-NEXT:     0x46 R_LARCH_32 .debug_line_str 0x9
 ; CHECK-NEXT:     0x4F R_LARCH_64 .L0 0x0
-; RELAX-NEXT:     0x5F R_LARCH_ADD16 .L0 0x0
-; RELAX-NEXT:     0x5F R_LARCH_SUB16 .L0 0x0
+; CHECK-NEXT:     0x5F R_LARCH_ADD16 .L0 0x0
+; CHECK-NEXT:     0x5F R_LARCH_SUB16 .L0 0x0
 ; CHECK-NEXT:   }
 ; CHECK-NEXT: ]