[llvm-dev] status of IPO/IPCP?

[Davide Italiano via llvm-dev]

On Tue, May 3, 2016 at 11:01 PM, Justin Bogner <mail at justinbogner.com> wrote:
> Sean Silva via llvm-dev <llvm-dev at lists.llvm.org> writes:
>> No tests fail with the patch below, so I would say it's pretty useless. It
>> seems that the C bindings are the only user but we can probably just have them
>> return IPSCCP instead.
>
> I don't necessarily think your conclusion is wrong, but the patch isn't
> proving what you think it's proving. In fact, the below passes all tests
> as well. When you call passes through `opt` they don't end up calling
> through the createXYZPass path.
>
> diff --git a/lib/Transforms/IPO/IPConstantPropagation.cpp b/lib/Transforms/IPO/IPConstantPropagation.cpp
> index b3ee499..8d70b98 100644
> --- a/lib/Transforms/IPO/IPConstantPropagation.cpp
> +++ b/lib/Transforms/IPO/IPConstantPropagation.cpp
> @@ -253,7 +253,9 @@ char IPCP::ID = 0;
>  INITIALIZE_PASS(IPCP, "ipconstprop",
>                  "Interprocedural constant propagation", false, false)
>
> -ModulePass *llvm::createIPConstantPropagationPass() { return new IPCP(); }
> +ModulePass *llvm::createIPConstantPropagationPass() {
> +  llvm_unreachable("fnord");
> +}
>

I think this should do the job:

$ grep -R 'ipconstprop' * | wc -l
   7
$ sed -i.bak 's/ipconstprop/ipsccp/' *
$ grep -R 'ipconstprop' * | wc -l
       0

and two tests are actually failing :|

Testing Time: 0.10s
********************
Failing Tests (2):
    LLVM :: Transforms/IPConstantProp/return-argument.ll
    LLVM :: Transforms/IPConstantProp/return-constants.ll

  Expected Passes    : 11
  Unexpected Failures: 2

I'll take a closer look tomorrow.

>  bool IPCP::runOnModule(Module &M) {
>    if (skipModule(M))
>
>> Any idea why this wasn't removed when IPSCCP was introduced? Probably worth
>> understanding that before ripping it out, but in the current state of things I
>> don't think removing it will be problematic.
>>
>> diff --git a/llvm/lib/Transforms/IPO/IPConstantPropagation.cpp b/llvm/lib/
>> Transforms/IPO/IPConstantPropagation.cpp
>> index a1533b3..24aea5c 100644
>> --- a/llvm/lib/Transforms/IPO/IPConstantPropagation.cpp
>> +++ b/llvm/lib/Transforms/IPO/IPConstantPropagation.cpp
>> @@ -51,7 +51,9 @@ char IPCP::ID = 0;
>>  INITIALIZE_PASS(IPCP, "ipconstprop",
>>                  "Interprocedural constant propagation", false, false)
>>
>> -ModulePass *llvm::createIPConstantPropagationPass() { return new IPCP(); }
>> +ModulePass *llvm::createIPConstantPropagationPass() {
>> +  return createIPSCCPPass();
>> +}
>>
>>  bool IPCP::runOnModule(Module &M) {
>>    if (skipModule(M))
>>
>> -- Sean Silva
>>
>> On Tue, May 3, 2016 at 3:06 PM, Davide Italiano via llvm-dev <
>> llvm-dev at lists.llvm.org> wrote:
>>
>>     The pass is pretty rudimental (as the comment at the top of the file
>>     hints), and it seems LLVM already has IPSCCP (which should do a better
>>     job at interprocedural constant propagation).
>>     I'm also not entirely sure it's used anywhere.
>>     Is there any reason to keep it around?
>>
>>     Thanks,
>>
>>     --
>>     Davide
>>
>>     "There are no solved problems; there are only problems that are more
>>     or less solved" -- Henri Poincare
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-- 
Davide

"There are no solved problems; there are only problems that are more
or less solved" -- Henri Poincare