[all-commits] [llvm/llvm-project] c47df3: [lldb][test] Make vector operator[] return T& to w...

[David Spickett via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: c47df3e8c8f47bab8a8302757c50710e0e1c43fb
      https://github.com/llvm/llvm-project/commit/c47df3e8c8f47bab8a8302757c50710e0e1c43fb
  Author: David Spickett <david.spickett at linaro.org>
  Date:   2024-10-21 (Mon, 21 Oct 2024)

  Changed paths:
    M lldb/test/Shell/Recognizer/Inputs/verbose_trap-in-stl.cpp

  Log Message:
  -----------
  [lldb][test] Make vector operator[] return T& to workaround Arm codegen issue

Since https://github.com/llvm/llvm-project/pull/109628 landed, this test
has been failing on 32-bit Arm.

This is due to a codegen problem (whether added or uncovered by the change,
not known) where the trap instruction is placed after the frame pointer
and link register are restored.

https://github.com/llvm/llvm-project/issues/113154

So the code was:
```
std::__1::vector<int>::operator[](unsigned int):
  sub sp, sp, #8
  str r0, [sp, #4]
  str r1, [sp]
  add sp, sp, #8
  .inst 0xe7ffdefe
  bx lr
```
When lldb saw the trap, the PC was inside operator[] but the frame
information actually pointed to g.

This bug only happens for leaf functions so adding a return type
works around it:
```
std::__1::vector<int>::operator[](unsigned int):
  push {r11, lr}
  mov r11, sp
  sub sp, sp, #8
  str r0, [sp, #4]
  str r1, [sp]
  mov sp, r11
  pop {r11, lr}
  .inst 0xe7ffdefe
  bx lr
```
(and operator[] should return T& anyway)

Now the PC location and frame information should match and the
test passes.



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