[llvm] [LoongArch] Insert nops and emit align reloc when handle alignment directive (PR #72962)

[Lu Weining via llvm-commits]

================
@@ -0,0 +1,53 @@
+# RUN: llvm-mc --filetype=obj --triple=loongarch64 --mattr=-relax %s \
+# RUN:     | llvm-readelf -rs - | FileCheck %s --check-prefix=NORELAX
+# RUN: llvm-mc --filetype=obj --triple=loongarch64 --mattr=+relax %s \
+# RUN:     | llvm-readelf -rs - | FileCheck %s --check-prefix=RELAX
+# RUN: llvm-mc --filetype=obj --triple=loongarch64 --mattr=+relax %s \
+# RUN:     | llvm-objdump -d - | FileCheck -check-prefix=RELAX-INST %s
+
+# NORELAX: There are no relocations in this file.
+# NORELAX: Symbol table '.symtab' contains 1 entries:
+
+# RELAX:       0000000000000000  0000000100000066 R_LARCH_ALIGN          0000000000000000 {{.*}} + 4
+# RELAX-NEXT:  0000000000000010  0000000100000066 R_LARCH_ALIGN          0000000000000000 {{.*}} + 5
+# RELAX-NEXT:  000000000000002c  0000000100000066 R_LARCH_ALIGN          0000000000000000 {{.*}} + 4
+# RELAX-NEXT:  000000000000003c  0000000100000066 R_LARCH_ALIGN          0000000000000000 {{.*}} + b04
+# RELAX-NEXT:  0000000000000048  0000000100000066 R_LARCH_ALIGN          0000000000000000 {{.*}} + 4
+# RELAX-EMPTY:
+# RELAX:       0000000000000000  0000000200000066 R_LARCH_ALIGN          0000000000000000 <null> + 4
+# RELAX-EMPTY:
+# RELAX:       Symbol table '.symtab' contains 3 entries:
+# RELAX:       0: 0000000000000000     0 NOTYPE  LOCAL  DEFAULT   UND
+# RELAX-NEXT:  1: 0000000000000000     0 NOTYPE  LOCAL  DEFAULT     2
+# RELAX-NEXT:  2: 0000000000000000     0 NOTYPE  LOCAL  DEFAULT     4
+
+.text
+.p2align 4        # A = 0x0
+nop
+.p2align 5        # B = A + 3 * NOP + NOP = 0x10
+.p2align 4        # C = B + 7 * NOP = 0x2C
+nop
+.p2align 4, , 11  # D = C + 3 * NOP + NOP = 0x3C
+## Not emit the third parameter.
+.p2align 4, , 12  # E = D + 3 * NOP = 0x48
+                  # END = E + 3 * NOP = 0x54 = 21 * NOP
+
+## Not emit R_LARCH_ALIGN if code alignment great than alignment directive.
+.p2align 2
+.p2align 1
+.p2align 0
+## Not emit instructions if max emit bytes less than min nop size.
+.p2align 4, , 2
+## Not emit R_LARCH_ALIGN if alignment directive with specific padding value.
----------------
SixWeining wrote:

```suggestion
## Not emit R_LARCH_ALIGN if alignment directive with specific padding value.
## The behavior is the same as GNU assembler.
```

https://github.com/llvm/llvm-project/pull/72962