Fix PR80275

On 2017.04.03 at 11:16 +0200, Richard Biener wrote:
> 
> The following extends split_address_to_core_and_offset to handle
> POINTER_PLUS_EXPR to be able to simplify
> (unsigned long) &MEM[(void *)&D.15512 + 12B] - (unsigned long) ((const int 
> *) &D.15512 + 4) which appears during niter analysis.
> 
> We seem to have various copies of similar code but refactoring didn't
> seem appropriate at this stage so I went for the minimal fix.
> 
> Bootstrap and regtest running on x86_64-unknown-linux-gnu.
> 
> Richard.
> 
> 2017-04-03  Richard Biener  <rguenther@suse.de>
> 
> 	PR tree-optimization/80275
> 	* fold-const.c (split_address_to_core_and_offset): Handle
> 	POINTER_PLUS_EXPR.
> 
> 	* g++.dg/opt/pr80275.C: New testcase.
> 
> Index: gcc/fold-const.c
> ===================================================================
> --- gcc/fold-const.c	(revision 246642)
> +++ gcc/fold-const.c	(working copy)
> @@ -14341,6 +14341,24 @@ split_address_to_core_and_offset (tree e
>  				  &volatilep);
>        core = build_fold_addr_expr_loc (loc, core);
>      }
> +  else if (TREE_CODE (exp) == POINTER_PLUS_EXPR)
> +    {
> +      core = TREE_OPERAND (exp, 0);
> +      STRIP_NOPS (core);
> +      *pbitpos = 0;
> +      *poffset = TREE_OPERAND (exp, 1);
> +      if (TREE_CODE (*poffset) == INTEGER_CST)
> +	{
> +	  offset_int tem = wi::sext (wi::to_offset (*poffset),
> +				     TYPE_PRECISION (TREE_TYPE (*poffset)));
> +	  tem <<= LOG2_BITS_PER_UNIT;
> +	  if (wi::fits_shwi_p (tem))
> +	    {
> +	      *pbitpos = tem.to_shwi ();
> +	      *poffset = NULL_TREE;
> +	    }
> +	}
> +    }
>    else
>      {
>        core = exp;
> Index: gcc/testsuite/g++.dg/opt/pr80275.C
> ===================================================================
> --- gcc/testsuite/g++.dg/opt/pr80275.C	(nonexistent)
> +++ gcc/testsuite/g++.dg/opt/pr80275.C	(working copy)
> @@ -0,0 +1,16 @@
> +// { dg-do compile { target c++14 } }
> +// { dg-options "-O2 -fdump-tree-optimized" }
> +
> +#include <algorithm>
> +
> +int g()
> +{
> +      return 1234;
> +}
> +
> +int f2()
> +{
> +      return std::min({1, g(), 4});
> +}
> +
> +// { dg-final { scan-tree-dump "return 1;" "optimized" } }

The testcase fails with -fpic, e.g.:
https://gcc.gnu.org/ml/gcc-regression/2017-04/msg00002.html

So perhaps:

On Tue, 4 Apr 2017, Markus Trippelsdorf wrote:

> On 2017.04.03 at 11:16 +0200, Richard Biener wrote:
>>
>> The following extends split_address_to_core_and_offset to handle
>> POINTER_PLUS_EXPR to be able to simplify
>> (unsigned long) &MEM[(void *)&D.15512 + 12B] - (unsigned long) ((const int
>> *) &D.15512 + 4) which appears during niter analysis.
>>
>> We seem to have various copies of similar code but refactoring didn't
>> seem appropriate at this stage so I went for the minimal fix.
>>
>> Bootstrap and regtest running on x86_64-unknown-linux-gnu.
>>
>> Richard.
>>
>> 2017-04-03  Richard Biener  <rguenther@suse.de>
>>
>> 	PR tree-optimization/80275
>> 	* fold-const.c (split_address_to_core_and_offset): Handle
>> 	POINTER_PLUS_EXPR.
>>
>> 	* g++.dg/opt/pr80275.C: New testcase.
>>
>> Index: gcc/fold-const.c
>> ===================================================================
>> --- gcc/fold-const.c	(revision 246642)
>> +++ gcc/fold-const.c	(working copy)
>> @@ -14341,6 +14341,24 @@ split_address_to_core_and_offset (tree e
>>  				  &volatilep);
>>        core = build_fold_addr_expr_loc (loc, core);
>>      }
>> +  else if (TREE_CODE (exp) == POINTER_PLUS_EXPR)
>> +    {
>> +      core = TREE_OPERAND (exp, 0);
>> +      STRIP_NOPS (core);
>> +      *pbitpos = 0;
>> +      *poffset = TREE_OPERAND (exp, 1);
>> +      if (TREE_CODE (*poffset) == INTEGER_CST)
>> +	{
>> +	  offset_int tem = wi::sext (wi::to_offset (*poffset),
>> +				     TYPE_PRECISION (TREE_TYPE (*poffset)));
>> +	  tem <<= LOG2_BITS_PER_UNIT;
>> +	  if (wi::fits_shwi_p (tem))
>> +	    {
>> +	      *pbitpos = tem.to_shwi ();
>> +	      *poffset = NULL_TREE;
>> +	    }
>> +	}
>> +    }
>>    else
>>      {
>>        core = exp;
>> Index: gcc/testsuite/g++.dg/opt/pr80275.C
>> ===================================================================
>> --- gcc/testsuite/g++.dg/opt/pr80275.C	(nonexistent)
>> +++ gcc/testsuite/g++.dg/opt/pr80275.C	(working copy)
>> @@ -0,0 +1,16 @@
>> +// { dg-do compile { target c++14 } }
>> +// { dg-options "-O2 -fdump-tree-optimized" }
>> +
>> +#include <algorithm>
>> +
>> +int g()
>> +{
>> +      return 1234;
>> +}
>> +
>> +int f2()
>> +{
>> +      return std::min({1, g(), 4});
>> +}
>> +
>> +// { dg-final { scan-tree-dump "return 1;" "optimized" } }
>
> The testcase fails with -fpic, e.g.:
> https://gcc.gnu.org/ml/gcc-regression/2017-04/msg00002.html
>
> So perhaps:
>
> diff --git a/gcc/testsuite/g++.dg/opt/pr80275.C b/gcc/testsuite/g++.dg/opt/pr80275.C
> index 7296a07fb2dd..7d625f2c7757 100644
> --- a/gcc/testsuite/g++.dg/opt/pr80275.C
> +++ b/gcc/testsuite/g++.dg/opt/pr80275.C
> @@ -1,4 +1,4 @@
> -// { dg-do compile { target c++14 } }
> +// { dg-do compile { target c++14 && nonpic } }
> // { dg-options "-O2 -fdump-tree-optimized" }
>
> #include <algorithm>

Making g static should work even with PIC.