[lld] [lld][ELF] Support relax R_LARCH_ALIGN (PR #78692)

[Jinyang He via llvm-commits]

================
@@ -0,0 +1,126 @@
+# REQUIRES: loongarch
+
+# RUN: llvm-mc --filetype=obj --triple=loongarch32 --mattr=+relax %s -o %t.32.o
+# RUN: llvm-mc --filetype=obj --triple=loongarch64 --mattr=+relax %s -o %t.64.o
+# RUN: ld.lld --section-start=.text=0x10000 --section-start=.text2=0x20000 -e 0 %t.32.o -o %t.32
+# RUN: ld.lld --section-start=.text=0x10000 --section-start=.text2=0x20000 -e 0 %t.64.o -o %t.64
+# RUN: ld.lld --section-start=.text=0x10000 --section-start=.text2=0x20000 -e 0 %t.32.o --no-relax -o %t.32n
+# RUN: ld.lld --section-start=.text=0x10000 --section-start=.text2=0x20000 -e 0 %t.64.o --no-relax -o %t.64n
+# RUN: llvm-objdump -td --no-show-raw-insn %t.32 | FileCheck %s
+# RUN: llvm-objdump -td --no-show-raw-insn %t.64 | FileCheck %s
+# RUN: llvm-objdump -td --no-show-raw-insn %t.32n | FileCheck %s
+# RUN: llvm-objdump -td --no-show-raw-insn %t.64n | FileCheck %s
+
+## Test the R_LARCH_ALIGN without symbol index.
+# RUN: llvm-mc --filetype=obj --triple=loongarch64 --mattr=+relax %s -o %t.o64.o --defsym=old=1
+# RUN: ld.lld --section-start=.text=0x10000 --section-start=.text2=0x20000 -e 0 %t.o64.o -o %t.o64
+# RUN: ld.lld --section-start=.text=0x10000 --section-start=.text2=0x20000 -e 0 %t.o64.o --no-relax -o %t.o64n
+# RUN: llvm-objdump -td --no-show-raw-insn %t.o64 | FileCheck %s
+# RUN: llvm-objdump -td --no-show-raw-insn %t.o64n | FileCheck %s
+
+## -r keeps section contents unchanged.
+# RUN: ld.lld -r %t.64.o -o %t.64.r
+# RUN: llvm-objdump -dr --no-show-raw-insn %t.64.r | FileCheck %s --check-prefix=CHECKR
+
+# CHECK-DAG: {{0*}}10000 l .text  {{0*}}44 .Ltext_start
+# CHECK-DAG: {{0*}}10038 l .text  {{0*}}0c .L1
+# CHECK-DAG: {{0*}}10040 l .text  {{0*}}04 .L2
+# CHECK-DAG: {{0*}}20000 l .text2 {{0*}}14 .Ltext2_start
+
+# CHECK:      <.Ltext_start>:
+# CHECK-NEXT:   break 1
+# CHECK-NEXT:   break 2
+# CHECK-NEXT:   nop
+# CHECK-NEXT:   nop
+# CHECK-NEXT:   break 3
+# CHECK-NEXT:   break 4
+# CHECK-NEXT:   nop
+# CHECK-NEXT:   nop
+# CHECK-NEXT:   pcalau12i     $a0, 0
+# CHECK-NEXT:   addi.{{[dw]}} $a0, $a0, 0
+# CHECK-NEXT:   pcalau12i     $a0, 0
+# CHECK-NEXT:   addi.{{[dw]}} $a0, $a0, 56
+# CHECK-NEXT:   pcalau12i     $a0, 0
+# CHECK-NEXT:   addi.{{[dw]}} $a0, $a0, 64
+# CHECK-EMPTY:
+# CHECK-NEXT: <.L1>:
+# CHECK-NEXT:   nop
+# CHECK-NEXT:   nop
+# CHECK-EMPTY:
+# CHECK-NEXT: <.L2>:
+# CHECK-NEXT:   break 5
+
+# CHECK:      <.Ltext2_start>:
+# CHECK-NEXT:   pcalau12i     $a0, 0
+# CHECK-NEXT:   addi.{{[dw]}} $a0, $a0, 0
+# CHECK-NEXT:   nop
+# CHECK-NEXT:   nop
+# CHECK-NEXT:   break 6
+
+# CHECKR:      <.Ltext2_start>:
+# CHECKR-NEXT:   pcalau12i $a0, 0
+# CHECKR-NEXT:   {{0*}}00: R_LARCH_PCALA_HI20 .Ltext2_start
+# CHECKR-NEXT:   {{0*}}00: R_LARCH_RELAX      *ABS*
+# CHECKR-NEXT:   addi.d    $a0, $a0, 0
+# CHECKR-NEXT:   {{0*}}04: R_LARCH_PCALA_LO12 .Ltext2_start
+# CHECKR-NEXT:   {{0*}}04: R_LARCH_RELAX      *ABS*
+# CHECKR-NEXT:   nop
+# CHECKR-NEXT:   {{0*}}08: R_LARCH_ALIGN      .Lalign_symbol+0x4
+# CHECKR-NEXT:   nop
+# CHECKR-NEXT:   nop
+# CHECKR-NEXT:   break 6
+
+.macro .fake_p2align_4 max=0
+  .ifdef old
+    .if \max==0
+      .reloc ., R_LARCH_ALIGN, 0xc
+      nop; nop; nop
+    .endif
+  .else
+    .reloc ., R_LARCH_ALIGN, .Lalign_symbol + 0x4 + (\max << 8)
+    nop; nop; nop
+  .endif
+.endm
+
+  .text
+.Lalign_symbol:
+.Ltext_start:
+  break 1
+  break 2
+## +0x8: Emit 2 nops, delete 1 nop.
+  .fake_p2align_4
+
+  break 3
+## +0x14: Emit 3 nops > 8 bytes, not emit.
+  .fake_p2align_4 8
+
+  break 4
+  .fake_p2align_4 8
+## +0x18: Emit 2 nops <= 8 bytes.
+
+## Compensate
+.ifdef old
+  nop; nop
+.endif
+
+## +0x20: Test symbol value and symbol size can be handled.
----------------
MQ-mengqing wrote:

I think it is enough for check symbol value. `.Ltext_start` checks value is not changed but size is changed.  `.L1` checks value is changed and size is changed.  `.L2` checks value is changed but size is not changed.

https://github.com/llvm/llvm-project/pull/78692