| Issue |
137739
|
| Summary |
UB optimization leads to really bad code gen
|
| Labels |
new issue
|
| Assignees |
|
| Reporter |
bwendling
|
Linux has some code that may result in dividing by zero or shifting by negative numbers. For instance, in one of the ARMGPU drivers, a "divide by zero" results in a fall through into the following function.
```
drivers/gpu/drm/amd/amdgpu/../display/dc/basics/fixpt31_32.o:
warning: objtool: dc_fixpt_recip() falls through to next function dc_fixpt_sinc()
drivers/gpu/drm/amd/amdgpu/../display/dc/sspl/spl_fixpt31_32.o:
warning: objtool: spl_fixpt_recip() falls through to next function spl_fixpt_sinc()
```
It is undefined behavior, but in these cases it will silently generate incorrect code. It's far better to generate the bad code so that it signals/traps/whatever.
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