[llvm-commits] PCH fix

[Devang Patel]

Anton,

This patch is good. I installed this patch in mainline sources. I  
agree, this should also go in 2.0 release branch.

Thanks Anton for taking care of this bug.
-
Devang

On May 17, 2007, at 2:53 AM, Anton Korobeynikov wrote:

> Hello, Everyone.
>
> Attached patch fixes PCHs for both TOT and 2.0 release.
>
> There were 2 problems:
>
> 1. flush() method of oFILEstream doesn't actually flush the file. This
> can lead to incorrect offsets calculations in the PCH handling code  
> and
> junk output. This problem seems to be highly platform-dependent: it
> fails for linux & mingw32, but passes for darwin.
>
> There are two possible solutions: either use stdio_sync_buf for
> oFILEstream or flush the asm_out_file by hands. I preferred second.
>
> 2. This problem is not platform specific. We have the following  
> sequence
> of calls during PCH's read:
>
>  1) llvm_start_asm_file()
>  2) llvm_read_pch()
>  3) llvm_end_asm_file()
>
> In llvm_start_asm_file() routine 2 FunctionPassManagers
> (PerFunctionPasses and CodeGenPasses) are created having TheModule  
> used
> during construction, later in the llvm_read_pch() TheModule is  
> freed and
> recreated, but ... PassManagers still holds pointer to old module.  
> This
> causes uninitialised memory reads (and segfaults later) during
> doFinalization() calls in the llvm_end_asm_file().
>
> The solutions was: factor out passmanagers' creation code to separate
> routine and call it in llvm_read_pch() in order to recreate passes.
>
> I think, this patch should be propagated to 2.0 release branch, or,
> otherwise PCHs should be marked as "broken in 2.0".
>
> Patch tested with Qt compilation on x86/linux.
> <pch_fix.diff>