[llvm] [LoongArch] Add debug location for register reload (PR #122057)

[via llvm-commits]

https://github.com/wangleiat created https://github.com/llvm/llvm-project/pull/122057

Although the automatically inserted reload instruction in the `Epilogue`
is unrelated to the original code, in order to improve debugger
functionality, we have re-added debugging location information in the
reload instruction. When using an empty debugging location, the
following issue occurs:
```
loongson at linux:~$ cat -n test.c
 1  int printf(const char *, ...);
 2  int main(int argc, char **argv) {
 3    printf("%d\n", argc);
 4    return 0;
 5  }
 clang -g -O0 test.c -o test
```
Without this patch, the debugger is unable to correctly access the
current stack information when a breakpoint is set on line 4:

```
loongson at linux:~$ gdb -q ./test
Reading symbols from ./test...
(gdb) break 4
Breakpoint 1 at 0x7c0: file test.c, line 4.
(gdb) run
Starting program: /home/wanglei/test
[Thread debugging using libthread_db enabled]
Using host libthread_db library "/lib/loongarch64-linux-gnu/libthread_db.so.1".
1

Breakpoint 1, main (argc=<error reading variable: Cannot access memory at address 0xffffffffffffffe8>,
    argv=<error reading variable: Cannot access memory at address 0xffffffffffffffe0>) at test.c:4
4         return 0;
```


>From 55991a51966d955314fb463ac547ee371e0ad7ba Mon Sep 17 00:00:00 2001
From: wanglei <wanglei at loongson.cn>
Date: Wed, 8 Jan 2025 14:50:34 +0800
Subject: [PATCH] =?UTF-8?q?[=F0=9D=98=80=F0=9D=97=BD=F0=9D=97=BF]=20initia?=
 =?UTF-8?q?l=20version?=
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Created using spr 1.3.5-bogner
---
 llvm/lib/Target/LoongArch/LoongArchInstrInfo.cpp | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/llvm/lib/Target/LoongArch/LoongArchInstrInfo.cpp b/llvm/lib/Target/LoongArch/LoongArchInstrInfo.cpp
index 54aeda28364003..32bc8bb8012957 100644
--- a/llvm/lib/Target/LoongArch/LoongArchInstrInfo.cpp
+++ b/llvm/lib/Target/LoongArch/LoongArchInstrInfo.cpp
@@ -154,6 +154,9 @@ void LoongArchInstrInfo::loadRegFromStackSlot(MachineBasicBlock &MBB,
                                               Register VReg) const {
   MachineFunction *MF = MBB.getParent();
   MachineFrameInfo &MFI = MF->getFrameInfo();
+  DebugLoc DL;
+  if (I != MBB.end())
+    DL = I->getDebugLoc();
 
   unsigned Opcode;
   if (LoongArch::GPRRegClass.hasSubClassEq(RC))
@@ -177,7 +180,7 @@ void LoongArchInstrInfo::loadRegFromStackSlot(MachineBasicBlock &MBB,
       MachinePointerInfo::getFixedStack(*MF, FI), MachineMemOperand::MOLoad,
       MFI.getObjectSize(FI), MFI.getObjectAlign(FI));
 
-  BuildMI(MBB, I, DebugLoc(), get(Opcode), DstReg)
+  BuildMI(MBB, I, DL, get(Opcode), DstReg)
       .addFrameIndex(FI)
       .addImm(0)
       .addMemOperand(MMO);