[PATCH] Fix PR80275

[Markus Trippelsdorf]

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>

-- 
Markus