clang-p2996/lldb/test/Shell/Recognizer/Inputs/verbose_trap-in-stl.cpp at 8fcb1263f42657ecbc355beff12500dfbcddee17 - clang-p2996 - Caio's Gitea

caio/clang-p2996

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David Spickett c47df3e8c8 [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.

2024-10-21 11:54:54 +00:00

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 namespace std {
 inline namespace __1 {
 template <typename T> struct vector {
   T& operator[](unsigned) { __builtin_verbose_trap("Bounds error", "out-of-bounds access"); }
 };
 } // namespace __1
 } // namespace std
 void g() {
   std::vector<int> v;
   v[10];
 }
 int main() {
   g();
   return 0;
 }