RE: [PATCH 2/2]middle-end: Support recognition of three-way max/min.

[Tamar Christina <Tamar.Christina@arm.com>]

> -----Original Message-----
> From: Richard Biener <rguenther@suse.de>
> Sent: Monday, June 20, 2022 9:36 AM
> To: Tamar Christina <Tamar.Christina@arm.com>
> Cc: gcc-patches@gcc.gnu.org; nd <nd@arm.com>; jakub@redhat.com
> Subject: Re: [PATCH 2/2]middle-end: Support recognition of three-way
> max/min.
> 
> On Thu, 16 Jun 2022, Tamar Christina wrote:
> 
> > Hi All,
> >
> > This patch adds support for three-way min/max recognition in phi-opts.
> >
> > Concretely for e.g.
> >
> > #include <stdint.h>
> >
> > uint8_t three_min (uint8_t xc, uint8_t xm, uint8_t xy) {
> > 	uint8_t	 xk;
> >     if (xc < xm) {
> >         xk = (uint8_t) (xc < xy ? xc : xy);
> >     } else {
> >         xk = (uint8_t) (xm < xy ? xm : xy);
> >     }
> >     return xk;
> > }
> >
> > we generate:
> >
> >   <bb 2> [local count: 1073741824]:
> >   _5 = MIN_EXPR <xc_1(D), xy_3(D)>;
> >   _7 = MIN_EXPR <xm_2(D), _5>;
> >   return _7;
> >
> > instead of
> >
> >   <bb 2>:
> >   if (xc_2(D) < xm_3(D))
> >     goto <bb 3>;
> >   else
> >     goto <bb 4>;
> >
> >   <bb 3>:
> >   xk_5 = MIN_EXPR <xc_2(D), xy_4(D)>;
> >   goto <bb 5>;
> >
> >   <bb 4>:
> >   xk_6 = MIN_EXPR <xm_3(D), xy_4(D)>;
> >
> >   <bb 5>:
> >   # xk_1 = PHI <xk_5(3), xk_6(4)>
> >   return xk_1;
> >
> > The same function also immediately deals with turning a minimization
> > problem into a maximization one if the results are inverted.  We do
> > this here since doing it in match.pd would end up changing the shape
> > of the BBs and adding additional instructions which would prevent various
> optimizations from working.
> 
> Can you explain a bit more?

I'll respond to this one first In case it changes how you want me to proceed.

I initially had used a match.pd rule to do the min to max conversion, but a
number of testcases started to fail.  The reason was that a lot of the foldings
checked that the BB contains only a single SSA and that that SSA is a phi node.

By changing the min into max, the negation of the result ends up In the same BB
and so the optimizations are skipped leading to less optimal code.

I did look into relaxing those phi opts but it felt like I'd make a rather arbitrary
exception for minus and seemed better to handle it in the minmax folding. 

Thanks,
Tamar

> 
> > Bootstrapped Regtested on aarch64-none-linux-gnu and no issues.
> >
> > Ok for master?
> >
> > Thanks,
> > Tamar
> >
> > gcc/ChangeLog:
> >
> > 	* tree-ssa-phiopt.cc (minmax_replacement): Optionally search for
> the phi
> > 	sequence of a three-way conditional.
> > 	(replace_phi_edge_with_variable): Support deferring of BB removal.
> > 	(tree_ssa_phiopt_worker): Detect diamond phi structure for three-
> way
> > 	min/max.
> > 	(strip_bit_not, invert_minmax_code): New.
> >
> > gcc/testsuite/ChangeLog:
> >
> > 	* gcc.dg/tree-ssa/split-path-1.c: Disable phi-opts so we don't
> optimize
> > 	code away.
> > 	* gcc.dg/tree-ssa/minmax-3.c: New test.
> > 	* gcc.dg/tree-ssa/minmax-4.c: New test.
> > 	* gcc.dg/tree-ssa/minmax-5.c: New test.
> > 	* gcc.dg/tree-ssa/minmax-6.c: New test.
> > 	* gcc.dg/tree-ssa/minmax-7.c: New test.
> > 	* gcc.dg/tree-ssa/minmax-8.c: New test.
> >
> > --- inline copy of patch --
> > diff --git a/gcc/testsuite/gcc.dg/tree-ssa/minmax-3.c
> > b/gcc/testsuite/gcc.dg/tree-ssa/minmax-3.c
> > new file mode 100644
> > index
> >
> 0000000000000000000000000000000000000000..de3b2e946e81701e3b75f580e
> 6a8
> > 43695a05786e
> > --- /dev/null
> > +++ b/gcc/testsuite/gcc.dg/tree-ssa/minmax-3.c
> > @@ -0,0 +1,17 @@
> > +/* { dg-do compile } */
> > +/* { dg-options "-O -fdump-tree-phiopt" } */
> > +
> > +#include <stdint.h>
> > +
> > +uint8_t three_min (uint8_t xc, uint8_t xm, uint8_t xy) {
> > +	uint8_t	 xk;
> > +    if (xc < xm) {
> > +        xk = (uint8_t) (xc < xy ? xc : xy);
> > +    } else {
> > +        xk = (uint8_t) (xm < xy ? xm : xy);
> > +    }
> > +    return xk;
> > +}
> > +
> > +/* { dg-final { scan-tree-dump-times "MIN_EXPR" 3 "phiopt1" } } */
> > +/* { dg-final { scan-tree-dump-times "MAX_EXPR" 0 "phiopt1" } } */
> > diff --git a/gcc/testsuite/gcc.dg/tree-ssa/minmax-4.c
> > b/gcc/testsuite/gcc.dg/tree-ssa/minmax-4.c
> > new file mode 100644
> > index
> >
> 0000000000000000000000000000000000000000..0b6d667be868c2405eaefd17c
> b52
> > 2da44bafa0e2
> > --- /dev/null
> > +++ b/gcc/testsuite/gcc.dg/tree-ssa/minmax-4.c
> > @@ -0,0 +1,17 @@
> > +/* { dg-do compile } */
> > +/* { dg-options "-O -fdump-tree-phiopt" } */
> > +
> > +#include <stdint.h>
> > +
> > +uint8_t three_max (uint8_t xc, uint8_t xm, uint8_t xy) {
> > +    uint8_t	 xk;
> > +    if (xc > xm) {
> > +        xk = (uint8_t) (xc > xy ? xc : xy);
> > +    } else {
> > +        xk = (uint8_t) (xm > xy ? xm : xy);
> > +    }
> > +    return xk;
> > +}
> > +
> > +/* { dg-final { scan-tree-dump-times "MIN_EXPR" 0 "phiopt1" } } */
> > +/* { dg-final { scan-tree-dump-times "MAX_EXPR" 3 "phiopt1" } } */
> > diff --git a/gcc/testsuite/gcc.dg/tree-ssa/minmax-5.c
> > b/gcc/testsuite/gcc.dg/tree-ssa/minmax-5.c
> > new file mode 100644
> > index
> >
> 0000000000000000000000000000000000000000..650601a3cc75d09a9e6e54a35f
> 5b
> > 9993074f8510
> > --- /dev/null
> > +++ b/gcc/testsuite/gcc.dg/tree-ssa/minmax-5.c
> > @@ -0,0 +1,17 @@
> > +/* { dg-do compile } */
> > +/* { dg-options "-O -fdump-tree-phiopt" } */
> > +
> > +#include <stdint.h>
> > +
> > +uint8_t three_minmax1 (uint8_t xc, uint8_t xm, uint8_t xy) {
> > +	uint8_t	 xk;
> > +    if (xc > xm) {
> > +        xk = (uint8_t) (xc < xy ? xc : xy);
> > +    } else {
> > +        xk = (uint8_t) (xm < xy ? xm : xy);
> > +    }
> > +    return xk;
> > +}
> > +
> > +/* { dg-final { scan-tree-dump-times "MIN_EXPR" 2 "phiopt1" } } */
> > +/* { dg-final { scan-tree-dump-times "MAX_EXPR" 1 "phiopt1" } } */
> > diff --git a/gcc/testsuite/gcc.dg/tree-ssa/minmax-6.c
> > b/gcc/testsuite/gcc.dg/tree-ssa/minmax-6.c
> > new file mode 100644
> > index
> >
> 0000000000000000000000000000000000000000..a628f6d99222958cfd8c410f0e
> 85
> > 639e3a49dd4b
> > --- /dev/null
> > +++ b/gcc/testsuite/gcc.dg/tree-ssa/minmax-6.c
> > @@ -0,0 +1,17 @@
> > +/* { dg-do compile } */
> > +/* { dg-options "-O -fdump-tree-phiopt" } */
> > +
> > +#include <stdint.h>
> > +
> > +uint8_t three_minmax3 (uint8_t xc, uint8_t xm, uint8_t xy) {
> > +        uint8_t  xk;
> > +    if (xc > xm) {
> > +        xk = (uint8_t) (xy < xc ? xc : xy);
> > +    } else {
> > +        xk = (uint8_t) (xm < xy ? xm : xy);
> > +    }
> > +    return xk;
> > +}
> > +
> > +/* { dg-final { scan-tree-dump-times "MIN_EXPR" 1 "phiopt1" } } */
> > +/* { dg-final { scan-tree-dump-times "MAX_EXPR" 1 "phiopt1" } } */
> > diff --git a/gcc/testsuite/gcc.dg/tree-ssa/minmax-7.c
> > b/gcc/testsuite/gcc.dg/tree-ssa/minmax-7.c
> > new file mode 100644
> > index
> >
> 0000000000000000000000000000000000000000..cb42412c4ada433b2f59df0a8b
> ef
> > 9fa7b1c5e104
> > --- /dev/null
> > +++ b/gcc/testsuite/gcc.dg/tree-ssa/minmax-7.c
> > @@ -0,0 +1,16 @@
> > +/* { dg-do compile } */
> > +/* { dg-options "-O -fdump-tree-phiopt" } */
> > +
> > +#include <stdint.h>
> > +
> > +uint8_t three_minmax2 (uint8_t xc, uint8_t xm, uint8_t xy) {
> > +	uint8_t	 xk;
> > +    if (xc > xm) {
> > +        xk = (uint8_t) (xc > xy ? xc : xy);
> > +    } else {
> > +        xk = (uint8_t) (xm < xy ? xm : xy);
> > +    }
> > +    return xk;
> > +}
> > +/* { dg-final { scan-tree-dump-times "MIN_EXPR" 1 "phiopt1" } } */
> > +/* { dg-final { scan-tree-dump-times "MAX_EXPR" 1 "phiopt1" } } */
> > diff --git a/gcc/testsuite/gcc.dg/tree-ssa/minmax-8.c
> > b/gcc/testsuite/gcc.dg/tree-ssa/minmax-8.c
> > new file mode 100644
> > index
> >
> 0000000000000000000000000000000000000000..9cd050e932376bc50bd6ae60c
> b65
> > 4fcab0bfdd1c
> > --- /dev/null
> > +++ b/gcc/testsuite/gcc.dg/tree-ssa/minmax-8.c
> > @@ -0,0 +1,17 @@
> > +/* { dg-do compile } */
> > +/* { dg-options "-O -fdump-tree-phiopt" } */
> > +
> > +#include <stdint.h>
> > +
> > +uint8_t three_minmax11 (uint8_t xc, uint8_t xm, uint8_t xy) {
> > +        uint8_t  xk;
> > +    if (xc < xm) {
> > +        xk = (uint8_t) (xc > xy ? xc : xy);
> > +    } else {
> > +        xk = (uint8_t) (xm > xy ? xm : xy);
> > +    }
> > +    return xk;
> > +}
> > +
> > +/* { dg-final { scan-tree-dump-times "MIN_EXPR" 1 "phiopt1" } } */
> > +/* { dg-final { scan-tree-dump-times "MAX_EXPR" 2 "phiopt1" } } */
> > diff --git a/gcc/testsuite/gcc.dg/tree-ssa/split-path-1.c
> > b/gcc/testsuite/gcc.dg/tree-ssa/split-path-1.c
> > index
> >
> 8b23ef4c7a3484cdc1647ee6d1b150f15685beff..902dde44a50e171b4f34ba724
> 7d7
> > 5a32d2c860ed 100644
> > --- a/gcc/testsuite/gcc.dg/tree-ssa/split-path-1.c
> > +++ b/gcc/testsuite/gcc.dg/tree-ssa/split-path-1.c
> > @@ -1,5 +1,5 @@
> >  /* { dg-do run } */
> > -/* { dg-options "-O2 -fsplit-paths -fdump-tree-split-paths-details
> > --param max-jump-thread-duplication-stmts=20" } */
> > +/* { dg-options "-O2 -fsplit-paths -fdump-tree-split-paths-details
> > +--param max-jump-thread-duplication-stmts=20 -fno-ssa-phiopt" } */
> >
> >  #include <stdio.h>
> >  #include <stdlib.h>
> > diff --git a/gcc/tree-ssa-phiopt.cc b/gcc/tree-ssa-phiopt.cc index
> >
> 562468b7f02a9ffe2713318add551902c14f89c3..6246f054006ff16e73602e7ce2e
> 3
> > 67d2d21421b1 100644
> > --- a/gcc/tree-ssa-phiopt.cc
> > +++ b/gcc/tree-ssa-phiopt.cc
> > @@ -62,8 +62,8 @@ static gphi *factor_out_conditional_conversion (edge,
> edge, gphi *, tree, tree,
> >  						gimple *);
> >  static int value_replacement (basic_block, basic_block,
> >  			      edge, edge, gphi *, tree, tree); -static bool
> > minmax_replacement (basic_block, basic_block,
> > -				edge, edge, gphi *, tree, tree);
> > +static bool minmax_replacement (basic_block, basic_block, basic_block,
> > +				edge, edge, gphi *, tree, tree, bool);
> >  static bool spaceship_replacement (basic_block, basic_block,
> >  				   edge, edge, gphi *, tree, tree);  static bool
> > cond_removal_in_builtin_zero_pattern (basic_block, basic_block, @@
> > -73,7 +73,7 @@ static bool cond_store_replacement (basic_block,
> basic_block, edge, edge,
> >  				    hash_set<tree> *);
> >  static bool cond_if_else_store_replacement (basic_block, basic_block,
> > basic_block);  static hash_set<tree> * get_non_trapping (); -static
> > void replace_phi_edge_with_variable (basic_block, edge, gphi *, tree);
> > +static void replace_phi_edge_with_variable (basic_block, edge, gphi
> > +*, tree, bool);
> >  static void hoist_adjacent_loads (basic_block, basic_block,
> >  				  basic_block, basic_block);
> >  static bool gate_hoist_loads (void);
> > @@ -199,6 +199,7 @@ tree_ssa_phiopt_worker (bool do_store_elim, bool
> do_hoist_loads, bool early_p)
> >        basic_block bb1, bb2;
> >        edge e1, e2;
> >        tree arg0, arg1;
> > +      bool diamond_minmax_p = false;
> >
> >        bb = bb_order[i];
> >
> > @@ -265,6 +266,29 @@ tree_ssa_phiopt_worker (bool do_store_elim,
> bool do_hoist_loads, bool early_p)
> >  	    hoist_adjacent_loads (bb, bb1, bb2, bb3);
> >  	  continue;
> >  	}
> > +      else if (EDGE_SUCC (bb1, 0)->dest == EDGE_SUCC (bb2, 0)->dest
> > +	       && single_succ_p (bb1)
> > +	       && single_succ_p (bb2)
> > +	       && single_pred_p (bb1)
> > +	       && single_pred_p (bb2)
> > +	       && single_succ_p (EDGE_SUCC (bb1, 0)->dest))
> 
> please do the single_succ/pred checks below where appropriate, also what's
> the last check about?  why does the merge block need a single successor?
> 
> > +	{
> > +	  gimple_stmt_iterator it1 = gsi_start_nondebug_after_labels_bb
> (bb1);
> > +	  gimple_stmt_iterator it2 = gsi_start_nondebug_after_labels_bb
> (bb2);
> > +	  if (gsi_one_before_end_p (it1) && gsi_one_before_end_p (it2))
> > +	    {
> > +	      gimple *stmt1 = gsi_stmt (it1);
> > +	      gimple *stmt2 = gsi_stmt (it2);
> > +	      if (is_gimple_assign (stmt1) && is_gimple_assign (stmt2))
> > +		{
> > +		  enum tree_code code1 = gimple_assign_rhs_code (stmt1);
> > +		  enum tree_code code2 = gimple_assign_rhs_code (stmt2);
> > +		  diamond_minmax_p
> > +		    = (code1 == MIN_EXPR || code1 == MAX_EXPR)
> > +		      && (code2 == MIN_EXPR || code2 == MAX_EXPR);
> > +		}
> > +	    }
> > +	}
> 
> I'd generalize this to general diamond detection, simply cutting off
> *_replacement workers that do not handle diamonds and do appropriate
> checks in minmax_replacement only.
> 
> >        else
> >  	continue;
> >
> > @@ -316,6 +340,13 @@ tree_ssa_phiopt_worker (bool do_store_elim,
> bool do_hoist_loads, bool early_p)
> >  	  if (!candorest)
> >  	    continue;
> >
> > +	  /* Check that we're looking for nested phis.  */
> > +	  if (phis == NULL && diamond_minmax_p)
> > +	    {
> > +	      phis = phi_nodes (EDGE_SUCC (bb2, 0)->dest);
> > +	      e2 = EDGE_SUCC (bb2, 0);
> > +	    }
> > +
> 
> instead
> 
>           basic_block merge = diamond_p ? EDGE_SUCC (bb2, 0)->dest : bb2;
>           gimple_seq phis = phi_nodes (merge);
> 
> 
> >  	  phi = single_non_singleton_phi_for_edges (phis, e1, e2);
> >  	  if (!phi)
> >  	    continue;
> > @@ -329,6 +360,7 @@ tree_ssa_phiopt_worker (bool do_store_elim, bool
> > do_hoist_loads, bool early_p)
> >
> >  	  gphi *newphi;
> >  	  if (single_pred_p (bb1)
> > +	      && !diamond_minmax_p
> >  	      && (newphi = factor_out_conditional_conversion (e1, e2, phi,
> >  							      arg0, arg1,
> >  							      cond_stmt)))
> > @@ -343,20 +375,25 @@ tree_ssa_phiopt_worker (bool do_store_elim,
> bool do_hoist_loads, bool early_p)
> >  	    }
> >
> >  	  /* Do the replacement of conditional if it can be done.  */
> > -	  if (!early_p && two_value_replacement (bb, bb1, e2, phi, arg0,
> arg1))
> > +	  if (!early_p
> > +	      && !diamond_minmax_p
> > +	      && two_value_replacement (bb, bb1, e2, phi, arg0, arg1))
> >  	    cfgchanged = true;
> > -	  else if (match_simplify_replacement (bb, bb1, e1, e2, phi,
> > -					       arg0, arg1,
> > -					       early_p))
> > +	  else if (!diamond_minmax_p
> > +		   && match_simplify_replacement (bb, bb1, e1, e2, phi,
> > +						  arg0, arg1, early_p))
> >  	    cfgchanged = true;
> >  	  else if (!early_p
> > +		   && !diamond_minmax_p
> >  		   && single_pred_p (bb1)
> >  		   && cond_removal_in_builtin_zero_pattern (bb, bb1, e1,
> e2,
> >  							    phi, arg0, arg1))
> >  	    cfgchanged = true;
> > -	  else if (minmax_replacement (bb, bb1, e1, e2, phi, arg0, arg1))
> > +	  else if (minmax_replacement (bb, bb1, bb2, e1, e2, phi, arg0, arg1,
> > +				       diamond_minmax_p))
> >  	    cfgchanged = true;
> >  	  else if (single_pred_p (bb1)
> > +		   && !diamond_minmax_p
> >  		   && spaceship_replacement (bb, bb1, e1, e2, phi, arg0,
> arg1))
> >  	    cfgchanged = true;
> >  	}
> > @@ -385,7 +422,7 @@ tree_ssa_phiopt_worker (bool do_store_elim, bool
> > do_hoist_loads, bool early_p)
> >
> >  static void
> >  replace_phi_edge_with_variable (basic_block cond_block,
> > -				edge e, gphi *phi, tree new_tree)
> > +				edge e, gphi *phi, tree new_tree, bool
> delete_bb = true)
> >  {
> >    basic_block bb = gimple_bb (phi);
> >    gimple_stmt_iterator gsi;
> > @@ -428,7 +465,7 @@ replace_phi_edge_with_variable (basic_block
> cond_block,
> >      edge_to_remove = EDGE_SUCC (cond_block, 1);
> >    else
> >      edge_to_remove = EDGE_SUCC (cond_block, 0);
> > -  if (EDGE_COUNT (edge_to_remove->dest->preds) == 1)
> > +  if (EDGE_COUNT (edge_to_remove->dest->preds) == 1 && delete_bb)
> 
> why do you need this change?
> 
> Did you check whether the new case works when the merge block has more
> than two incoming edges?
> 
> >      {
> >        e->flags |= EDGE_FALLTHRU;
> >        e->flags &= ~(EDGE_TRUE_VALUE | EDGE_FALSE_VALUE); @@ -
> 1564,15
> > +1601,52 @@ value_replacement (basic_block cond_bb, basic_block
> middle_bb,
> >    return 0;
> >  }
> >
> > +/* If VAR is an SSA_NAME that points to a BIT_NOT_EXPR then return the
> TREE for
> > +   the value being inverted.  */
> > +
> > +static tree
> > +strip_bit_not (tree var)
> > +{
> > +  if (TREE_CODE (var) != SSA_NAME)
> > +    return NULL_TREE;
> > +
> > +  gimple *assign = SSA_NAME_DEF_STMT (var);  if (gimple_code (assign)
> > + != GIMPLE_ASSIGN)
> > +    return NULL_TREE;
> > +
> > +  if (gimple_assign_rhs_code (assign) != BIT_NOT_EXPR)
> > +    return NULL_TREE;
> > +
> > +  return gimple_assign_rhs1 (assign); }
> > +
> > +/* Invert a MIN to a MAX or a MAX to a MIN expression CODE.  */
> > +
> > +enum tree_code
> > +invert_minmax_code (enum tree_code code) {
> > +  switch (code) {
> > +  case MIN_EXPR:
> > +    return MAX_EXPR;
> > +  case MAX_EXPR:
> > +    return MIN_EXPR;
> > +  default:
> > +    gcc_unreachable ();
> > +  }
> > +}
> > +
> >  /*  The function minmax_replacement does the main work of doing the
> minmax
> >      replacement.  Return true if the replacement is done.  Otherwise return
> >      false.
> >      BB is the basic block where the replacement is going to be done on.
> ARG0
> > -    is argument 0 from the PHI.  Likewise for ARG1.  */
> > +    is argument 0 from the PHI.  Likewise for ARG1.
> > +
> > +    If THREEWAY_P then expect the BB to be laid out in diamond shape with
> each
> > +    BB containing only a MIN or MAX expression.  */
> >
> >  static bool
> > -minmax_replacement (basic_block cond_bb, basic_block middle_bb,
> > -		    edge e0, edge e1, gphi *phi, tree arg0, tree arg1)
> > +minmax_replacement (basic_block cond_bb, basic_block middle_bb,
> basic_block alt_middle_bb,
> > +		    edge e0, edge e1, gphi *phi, tree arg0, tree arg1, bool
> > +threeway_p)
> >  {
> >    tree result;
> >    edge true_edge, false_edge;
> > @@ -1727,9 +1801,14 @@ minmax_replacement (basic_block cond_bb,
> basic_block middle_bb,
> >    if (false_edge->dest == middle_bb)
> >      false_edge = EDGE_SUCC (false_edge->dest, 0);
> >
> > +  /* When THREEWAY_P then e1 will point to the edge of the final
> transition
> > +     from middle-bb to end.  */
> >    if (true_edge == e0)
> >      {
> > -      gcc_assert (false_edge == e1);
> > +      if (threeway_p)
> > +	gcc_assert (false_edge == EDGE_PRED (e1->src, 0));
> > +      else
> > +	gcc_assert (false_edge == e1);
> >        arg_true = arg0;
> >        arg_false = arg1;
> >      }
> > @@ -1768,6 +1847,133 @@ minmax_replacement (basic_block cond_bb,
> basic_block middle_bb,
> >        else
> >  	return false;
> >      }
> > +  else if (middle_bb != alt_middle_bb && threeway_p)
> > +    {
> > +      /* Recognize the following case:
> > +
> > +	 if (smaller < larger)
> > +	   a = MIN (smaller, c);
> > +	 else
> > +	   b = MIN (larger, c);
> > +	 x = PHI <a, b>
> > +
> > +	 This is equivalent to
> > +
> > +	 a = MIN (smaller, c);
> > +	 x = MIN (larger, a);  */
> > +
> > +      gimple *assign = last_and_only_stmt (middle_bb);
> > +      tree lhs, op0, op1, bound;
> > +      tree alt_lhs, alt_op0, alt_op1;
> > +      bool invert = false;
> > +
> > +      if (!single_pred_p (middle_bb)
> > +	  || !single_pred_p (alt_middle_bb))
> > +	return false;
> > +
> > +      if (!assign
> > +	  || gimple_code (assign) != GIMPLE_ASSIGN)
> > +	return false;
> > +
> > +      lhs = gimple_assign_lhs (assign);
> > +      ass_code = gimple_assign_rhs_code (assign);
> > +      if (ass_code != MAX_EXPR && ass_code != MIN_EXPR)
> > +	return false;
> > +
> > +      op0 = gimple_assign_rhs1 (assign);
> > +      op1 = gimple_assign_rhs2 (assign);
> > +
> > +      assign = last_and_only_stmt (alt_middle_bb);
> > +      if (!assign
> > +	  || gimple_code (assign) != GIMPLE_ASSIGN)
> > +	return false;
> > +
> > +      alt_lhs = gimple_assign_lhs (assign);
> > +      if (ass_code != gimple_assign_rhs_code (assign))
> > +	return false;
> > +
> > +      alt_op0 = gimple_assign_rhs1 (assign);
> > +      alt_op1 = gimple_assign_rhs2 (assign);
> > +
> > +      if (!operand_equal_for_phi_arg_p (lhs, arg_true)
> > +	 || !operand_equal_for_phi_arg_p (alt_lhs, arg_false))
> > +	return false;
> > +
> > +      if ((operand_equal_for_phi_arg_p (op0, smaller)
> > +		|| (alt_smaller
> > +		    && operand_equal_for_phi_arg_p (op0, alt_smaller)))
> > +	       && (operand_equal_for_phi_arg_p (alt_op0, larger)
> > +		   || (alt_larger
> > +		       && operand_equal_for_phi_arg_p (alt_op0, alt_larger))))
> > +	{
> > +	  /* We got here if the condition is true, i.e., SMALLER < LARGER.  */
> > +	  if (!operand_equal_for_phi_arg_p (op1, alt_op1))
> > +	    return false;
> > +
> > +	  if ((arg0 = strip_bit_not (op0)) != NULL
> > +	      && (arg1 = strip_bit_not (alt_op0)) != NULL
> > +	      && (bound = strip_bit_not (op1)) != NULL)
> > +	    {
> > +	      minmax = MAX_EXPR;
> > +	      ass_code = invert_minmax_code (ass_code);
> > +	      invert = true;
> > +	    }
> > +	  else
> > +	    {
> > +	      bound = op1;
> > +	      minmax = MIN_EXPR;
> > +	      arg0 = op0;
> > +	      arg1 = alt_op0;
> > +	     }
> > +	}
> > +      else if ((operand_equal_for_phi_arg_p (op0, larger)
> > +		|| (alt_larger
> > +		    && operand_equal_for_phi_arg_p (op0, alt_larger)))
> > +	       && (operand_equal_for_phi_arg_p (alt_op0, smaller)
> > +		   || (alt_smaller
> > +		       && operand_equal_for_phi_arg_p (alt_op0,
> alt_smaller))))
> > +	{
> > +	  /* We got here if the condition is true, i.e., SMALLER > LARGER.  */
> > +	  if (!operand_equal_for_phi_arg_p (op1, alt_op1))
> > +	    return false;
> > +
> > +	  if ((arg0 = strip_bit_not (op0)) != NULL
> > +	      && (arg1 = strip_bit_not (alt_op0)) != NULL
> > +	      && (bound = strip_bit_not (op1)) != NULL)
> > +	    {
> > +	      minmax = MIN_EXPR;
> > +	      ass_code = invert_minmax_code (ass_code);
> > +	      invert = true;
> > +	    }
> > +	  else
> > +	    {
> > +	      bound = op1;
> > +	      minmax = MAX_EXPR;
> > +	      arg0 = op0;
> > +	      arg1 = alt_op0;
> > +	     }
> > +	}
> > +      else
> > +	return false;
> 
> Did you check you have coverage for all cases above in your testcases?
> 
> > +      /* Reset any range information from the basic block.  */
> > +      reset_flow_sensitive_info_in_bb (cond_bb);
> 
> Huh.  You need to reset flow-sensitive info of the middle-bb stmt that
> prevails only...
> 
> > +      /* Emit the statement to compute min/max.  */
> > +      gimple_seq stmts = NULL;
> > +      tree phi_result = PHI_RESULT (phi);
> > +      result = gimple_build (&stmts, minmax, TREE_TYPE (phi_result), arg0,
> bound);
> > +      result = gimple_build (&stmts, ass_code, TREE_TYPE
> > + (phi_result), result, arg1);
> 
> ... but you are re-building both here.  And also you drop locations, the
> preserved min/max should keep the old, the new should get the location of
> ... hmm, the condition possibly?
> 
> > +      if (invert)
> > +	result = gimple_build (&stmts, BIT_NOT_EXPR, TREE_TYPE
> (phi_result),
> > +result);
> > +
> > +      gsi = gsi_last_bb (cond_bb);
> > +      gsi_insert_seq_before (&gsi, stmts, GSI_NEW_STMT);
> > +
> > +      replace_phi_edge_with_variable (cond_bb, e1, phi, result, false);
> > +      return true;
> > +    }
> >    else
> >      {
> >        /* Recognize the following case, assuming d <= u:
> >
> >
> >
> >
> >
> 
> --
> Richard Biener <rguenther@suse.de>
> SUSE Software Solutions Germany GmbH, Frankenstraße 146, 90461
> Nuernberg, Germany; GF: Ivo Totev, Andrew Myers, Andrew McDonald,
> Boudien Moerman; HRB 36809 (AG Nuernberg)