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RFC [1/2] divmod transform

Message ID CAAgBjMnLkLUbASnivLA_OL+ddmtqB5+=sfAvg4buXip5=eaDqw@mail.gmail.com
State Superseded
Headers show

Commit Message

Prathamesh Kulkarni May 31, 2016, 1:08 p.m. UTC
On 30 May 2016 at 13:15, Richard Biener <rguenther@suse.de> wrote:
> On Mon, 30 May 2016, Prathamesh Kulkarni wrote:

>

>> The attached patch ICE's during bootstrap for x86_64, and is reproducible with

>> following case with -m32 -O2:

>>

>> typedef long long type;

>>

>> type f(type x, type y)

>> {

>>   type q = x / y;

>>   type r = x % y;

>>   return q + r;

>> }

>>

>> The ICE happens because the test-case hits

>> gcc_assert (unsignedp);

>> in default_expand_divmod_libfunc ().

>

> That's of course your function (and ICE).

>

>> Surprisingly, optab_libfunc (sdivmod_optab, DImode) returns optab_libfunc

>> with name "__divmoddi4" although __divmoddi4() is nowhere defined in

>> libgcc for x86.

>> (I verified that by forcing the patch to generate call to __divmoddi4,

>> which results in undefined reference to __divmoddi4).

>>

>> This happens because in optabs.def we have:

>> OPTAB_NL(sdivmod_optab, "divmod$a4", UNKNOWN, "divmod", '4', gen_int_libfunc)

>>

>> and gen_int_libfunc generates "__divmoddi4" on first call to optab_libfunc

>> and sets optab_libfunc (sdivmod_optab, DImode) to "__divmoddi4".

>> I wonder if we should remove gen_int_libfunc entry in optabs.def for

>> sdivmod_optab ?

>

> Hum, not sure - you might want to look at expand_divmod (though that

> always just computes one part of the result in the end).

As a workaround, would it be OK to check if libfunc is __udivmoddi4
if expand_divmod_libfunc is default, as in attached patch ?
This prevents ICE for the above test-case.
Bootstrap+test on x86_64 in progress.

Thanks,
Prathamesh
>

> Joseph - do you know sth about why there's not a full set of divmod

> libfuncs in libgcc?

>

> Thanks,

> Richard.
diff mbox

Patch

diff --git a/gcc/doc/tm.texi b/gcc/doc/tm.texi
index 8c7f2a1..111f19f 100644
--- a/gcc/doc/tm.texi
+++ b/gcc/doc/tm.texi
@@ -6963,6 +6963,12 @@  This is firstly introduced on ARM/AArch64 targets, please refer to
 the hook implementation for how different fusion types are supported.
 @end deftypefn
 
+@deftypefn {Target Hook} void TARGET_EXPAND_DIVMOD_LIBFUNC (bool @var{unsignedp}, machine_mode @var{mode}, @var{rtx}, @var{rtx}, rtx *@var{quot}, rtx *@var{rem})
+Define this hook if the port does not have hardware div and divmod insn for
+the given mode but has divmod libfunc, which is incompatible
+with libgcc2.c:__udivmoddi4
+@end deftypefn
+
 @node Sections
 @section Dividing the Output into Sections (Texts, Data, @dots{})
 @c the above section title is WAY too long.  maybe cut the part between
diff --git a/gcc/doc/tm.texi.in b/gcc/doc/tm.texi.in
index f963a58..2c9a800 100644
--- a/gcc/doc/tm.texi.in
+++ b/gcc/doc/tm.texi.in
@@ -4848,6 +4848,8 @@  them: try the first ones in this list first.
 
 @hook TARGET_SCHED_FUSION_PRIORITY
 
+@hook TARGET_EXPAND_DIVMOD_LIBFUNC
+
 @node Sections
 @section Dividing the Output into Sections (Texts, Data, @dots{})
 @c the above section title is WAY too long.  maybe cut the part between
diff --git a/gcc/internal-fn.c b/gcc/internal-fn.c
index c867ddc..0cb59f7 100644
--- a/gcc/internal-fn.c
+++ b/gcc/internal-fn.c
@@ -2276,6 +2276,48 @@  multi_vector_optab_supported_p (convert_optab optab, tree_pair types,
 #define direct_mask_store_optab_supported_p direct_optab_supported_p
 #define direct_store_lanes_optab_supported_p multi_vector_optab_supported_p
 
+/* Expand DIVMOD() using:
+ a) optab handler for udivmod/sdivmod if it is available.
+ b) If optab_handler doesn't exist, Generate call to
+    optab_libfunc for udivmod/sdivmod.  */
+
+static void 
+expand_DIVMOD (internal_fn, gcall *stmt)
+{
+  tree lhs = gimple_call_lhs (stmt);
+  tree arg0 = gimple_call_arg (stmt, 0);
+  tree arg1 = gimple_call_arg (stmt, 1);
+
+  gcc_assert (TREE_CODE (TREE_TYPE (lhs)) == COMPLEX_TYPE);
+  tree type = TREE_TYPE (TREE_TYPE (lhs));
+  machine_mode mode = TYPE_MODE (type);
+  bool unsignedp = TYPE_UNSIGNED (type);
+  optab tab = (unsignedp) ? udivmod_optab : sdivmod_optab;
+
+  rtx op0 = expand_normal (arg0);
+  rtx op1 = expand_normal (arg1);
+  rtx target = expand_expr (lhs, NULL_RTX, VOIDmode, EXPAND_WRITE);
+
+  rtx quotient, remainder;
+
+  /* Check if optab handler exists for [u]divmod.  */
+  if (optab_handler (tab, mode) != CODE_FOR_nothing)
+    {
+      quotient = gen_reg_rtx (mode);
+      remainder = gen_reg_rtx (mode);
+      expand_twoval_binop (tab, op0, op1, quotient, remainder, unsignedp);
+    }
+  else
+    targetm.expand_divmod_libfunc (unsignedp, mode, op0, op1,
+				   &quotient, &remainder);
+
+  /* Wrap the return value (quotient, remainder) within COMPLEX_EXPR.  */
+  expand_expr (build2 (COMPLEX_EXPR, TREE_TYPE (lhs),
+		       make_tree (TREE_TYPE (arg0), quotient),
+		       make_tree (TREE_TYPE (arg1), remainder)),
+	       target, VOIDmode, EXPAND_NORMAL);
+}
+
 /* Return true if FN is supported for the types in TYPES when the
    optimization type is OPT_TYPE.  The types are those associated with
    the "type0" and "type1" fields of FN's direct_internal_fn_info
diff --git a/gcc/internal-fn.def b/gcc/internal-fn.def
index e729d85..56a80f1 100644
--- a/gcc/internal-fn.def
+++ b/gcc/internal-fn.def
@@ -194,6 +194,9 @@  DEF_INTERNAL_FN (ATOMIC_BIT_TEST_AND_SET, ECF_LEAF | ECF_NOTHROW, NULL)
 DEF_INTERNAL_FN (ATOMIC_BIT_TEST_AND_COMPLEMENT, ECF_LEAF | ECF_NOTHROW, NULL)
 DEF_INTERNAL_FN (ATOMIC_BIT_TEST_AND_RESET, ECF_LEAF | ECF_NOTHROW, NULL)
 
+/* Divmod function.  */
+DEF_INTERNAL_FN (DIVMOD, ECF_CONST | ECF_LEAF, NULL)
+
 #undef DEF_INTERNAL_INT_FN
 #undef DEF_INTERNAL_FLT_FN
 #undef DEF_INTERNAL_OPTAB_FN
diff --git a/gcc/target.def b/gcc/target.def
index 6392e73..4496f9a 100644
--- a/gcc/target.def
+++ b/gcc/target.def
@@ -4948,6 +4948,16 @@  Normally, this is not needed.",
  bool, (const_tree field, machine_mode mode),
  default_member_type_forces_blk)
 
+/* See tree-ssa-math-opts.c:divmod_candidate_p for conditions that gate
+   the divmod transform.  */
+DEFHOOK
+(expand_divmod_libfunc,
+ "Define this hook if the port does not have hardware div and divmod insn for\n\
+the given mode but has divmod libfunc, which is incompatible\n\
+with libgcc2.c:__udivmoddi4",
+ void, (bool unsignedp, machine_mode mode, rtx, rtx, rtx *quot, rtx *rem),
+ default_expand_divmod_libfunc)
+
 /* Return the class for a secondary reload, and fill in extra information.  */
 DEFHOOK
 (secondary_reload,
diff --git a/gcc/targhooks.c b/gcc/targhooks.c
index 6b4601b..20327a6 100644
--- a/gcc/targhooks.c
+++ b/gcc/targhooks.c
@@ -1965,4 +1965,31 @@  default_optab_supported_p (int, machine_mode, machine_mode, optimization_type)
   return true;
 }
 
+/* Generate call to
+   DImode __udivmoddi4 (DImode op0, DImode op1, DImode *rem).  */
+
+void
+default_expand_divmod_libfunc (bool unsignedp, machine_mode mode,
+			       rtx op0, rtx op1,
+			       rtx *quot_p, rtx *rem_p)
+{
+  gcc_assert (mode == DImode);
+  gcc_assert (unsignedp);
+
+  rtx libfunc = optab_libfunc (udivmod_optab, DImode);
+  gcc_assert (libfunc);
+
+  rtx remainder = assign_stack_temp (DImode, GET_MODE_SIZE (DImode));
+  rtx address = XEXP (remainder, 0);
+
+  rtx quotient = emit_library_call_value (libfunc, NULL_RTX, LCT_CONST,
+					  DImode, 3,
+					  op0, GET_MODE (op0),
+					  op1, GET_MODE (op1),
+					  address, GET_MODE (address));
+
+  *quot_p = quotient;
+  *rem_p = remainder;
+}
+
 #include "gt-targhooks.h"
diff --git a/gcc/targhooks.h b/gcc/targhooks.h
index 7687c39..dc5e8e7 100644
--- a/gcc/targhooks.h
+++ b/gcc/targhooks.h
@@ -254,4 +254,7 @@  extern void default_setup_incoming_vararg_bounds (cumulative_args_t ca ATTRIBUTE
 extern bool default_optab_supported_p (int, machine_mode, machine_mode,
 				       optimization_type);
 
+extern void default_expand_divmod_libfunc (bool, machine_mode,
+					   rtx, rtx, rtx *, rtx *);
+
 #endif /* GCC_TARGHOOKS_H */
diff --git a/gcc/tree-ssa-math-opts.c b/gcc/tree-ssa-math-opts.c
index 81688cd..9bde79f 100644
--- a/gcc/tree-ssa-math-opts.c
+++ b/gcc/tree-ssa-math-opts.c
@@ -112,6 +112,9 @@  along with GCC; see the file COPYING3.  If not see
 #include "params.h"
 #include "internal-fn.h"
 #include "case-cfn-macros.h"
+#include "optabs-libfuncs.h"
+#include "tree-eh.h"
+#include "targhooks.h"
 
 /* This structure represents one basic block that either computes a
    division, or is a common dominator for basic block that compute a
@@ -184,6 +187,9 @@  static struct
 
   /* Number of fp fused multiply-add ops inserted.  */
   int fmas_inserted;
+
+  /* Number of divmod calls inserted.  */
+  int divmod_calls_inserted;
 } widen_mul_stats;
 
 /* The instance of "struct occurrence" representing the highest
@@ -3784,6 +3790,228 @@  match_uaddsub_overflow (gimple_stmt_iterator *gsi, gimple *stmt,
   return true;
 }
 
+/* Return true if target has support for divmod.  */
+
+static bool
+target_supports_divmod_p (optab divmod_optab, optab div_optab, machine_mode mode) 
+{
+  /* If target supports hardware divmod insn, use it for divmod.  */
+  if (optab_handler (divmod_optab, mode) != CODE_FOR_nothing)
+    return true;
+
+  /* Check if libfunc for divmod is available.  */
+  rtx libfunc = optab_libfunc (divmod_optab, mode);
+  if (libfunc != NULL_RTX)
+    {
+      /* If optab_handler exists for div_optab, perhaps in a wider mode,
+	 we don't want to use the libfunc even if it exists for given mode.  */ 
+      for (machine_mode div_mode = mode;
+	   div_mode != VOIDmode;
+	   div_mode = GET_MODE_WIDER_MODE (div_mode))
+	if (optab_handler (div_optab, div_mode) != CODE_FOR_nothing)
+	  return false;
+
+      /* FIXME: This is a hack to workaround an issue with optab_libfunc().
+	 optab_libfunc (sdivmod_optab, DImode) returns libfunc "__divmoddi4",
+	 although __divmoddi4() does not exist in libgcc. For now, enable the
+	 transform only if libfunc is guaranteed to be __udivmoddi4.  */
+      return (targetm.expand_divmod_libfunc != default_expand_divmod_libfunc
+	     || !strcmp (XSTR (libfunc, 0), "__udivmoddi4"));
+    }
+
+  return false;
+}
+
+/* Check if stmt is candidate for divmod transform.  */
+
+static bool
+divmod_candidate_p (gassign *stmt)
+{
+  tree type = TREE_TYPE (gimple_assign_lhs (stmt));
+  enum machine_mode mode = TYPE_MODE (type);
+  optab divmod_optab, div_optab;
+
+  if (TYPE_UNSIGNED (type))
+    {
+      divmod_optab = udivmod_optab;
+      div_optab = udiv_optab;
+    }
+  else
+    {
+      divmod_optab = sdivmod_optab;
+      div_optab = sdiv_optab;
+    }
+
+  tree op1 = gimple_assign_rhs1 (stmt);
+  tree op2 = gimple_assign_rhs2 (stmt);
+
+  /* Disable the transform if either is a constant, since division-by-constant
+     may have specialized expansion.  */
+  if (CONSTANT_CLASS_P (op1) || CONSTANT_CLASS_P (op2))
+    return false;
+
+  /* Exclude the case where TYPE_OVERFLOW_TRAPS (type) as that should
+     expand using the [su]divv optabs.  */
+  if (TYPE_OVERFLOW_TRAPS (type))
+    return false;
+  
+  if (!target_supports_divmod_p (divmod_optab, div_optab, mode)) 
+    return false;
+
+  return true;
+}
+
+/* This function looks for:
+   t1 = a TRUNC_DIV_EXPR b;
+   t2 = a TRUNC_MOD_EXPR b;
+   and transforms it to the following sequence:
+   complex_tmp = DIVMOD (a, b);
+   t1 = REALPART_EXPR(a);
+   t2 = IMAGPART_EXPR(b);
+   For conditions enabling the transform see divmod_candidate_p().
+
+   The pass works in two phases:
+   1) Walk through all immediate uses of stmt's operand and find a
+      TRUNC_DIV_EXPR with matching operands and if such a stmt is found add
+      it to stmts vector.
+   2) Insert DIVMOD call before first div/mod stmt in top_bb (basic block that
+      dominates other div/mod stmts with same operands) and update entries in
+      stmts vector to use return value of DIMOVD (REALEXPR_PART for div,
+      IMAGPART_EXPR for mod).  */
+
+static bool
+convert_to_divmod (gassign *stmt)
+{
+  if (!divmod_candidate_p (stmt))
+    return false;
+
+  tree op1 = gimple_assign_rhs1 (stmt);
+  tree op2 = gimple_assign_rhs2 (stmt);
+  
+  imm_use_iterator use_iter;
+  gimple *use_stmt;
+  auto_vec<gimple *> stmts; 
+
+  gimple *top_stmt = stmt; 
+  basic_block top_bb = gimple_bb (stmt);
+
+  /* Try to set top_stmt to "topmost" stmt
+     with code TRUNC_DIV_EXPR/TRUNC_MOD_EXPR having same operands as stmt.  */
+
+  FOR_EACH_IMM_USE_STMT (use_stmt, use_iter, op1)
+    {
+      if (is_gimple_assign (use_stmt)
+	  && (gimple_assign_rhs_code (use_stmt) == TRUNC_DIV_EXPR
+	      || gimple_assign_rhs_code (use_stmt) == TRUNC_MOD_EXPR)
+	  && operand_equal_p (op1, gimple_assign_rhs1 (use_stmt), 0)
+	  && operand_equal_p (op2, gimple_assign_rhs2 (use_stmt), 0))
+	{
+	  if (stmt_can_throw_internal (use_stmt))
+	    continue;
+
+	  basic_block bb = gimple_bb (use_stmt);
+
+	  if (bb == top_bb)
+	    {
+	      if (gimple_uid (use_stmt) < gimple_uid (top_stmt))
+		top_stmt = use_stmt;
+	    }
+	  else if (dominated_by_p (CDI_DOMINATORS, top_bb, bb))
+	    {
+	      top_bb = bb;
+	      top_stmt = use_stmt;
+	    }
+	}
+    }
+
+  if (top_stmt == stmt && stmt_can_throw_internal (top_stmt))
+    return false;
+
+  tree top_op1 = gimple_assign_rhs1 (top_stmt);
+  tree top_op2 = gimple_assign_rhs2 (top_stmt);
+
+  stmts.safe_push (top_stmt);
+  bool div_seen = (gimple_assign_rhs_code (top_stmt) == TRUNC_DIV_EXPR);
+
+  /* Ensure that gimple_bb (use_stmt) is dominated by top_bb.  */    
+
+  FOR_EACH_IMM_USE_STMT (use_stmt, use_iter, top_op1)
+    {
+      if (is_gimple_assign (use_stmt)
+	  && (gimple_assign_rhs_code (use_stmt) == TRUNC_DIV_EXPR
+	      || gimple_assign_rhs_code (use_stmt) == TRUNC_MOD_EXPR)
+	  && operand_equal_p (top_op1, gimple_assign_rhs1 (use_stmt), 0)
+	  && operand_equal_p (top_op2, gimple_assign_rhs2 (use_stmt), 0))
+	{
+	  if (use_stmt == top_stmt)
+	    continue;
+
+	  if (stmt_can_throw_internal (use_stmt))
+	    continue;
+
+	  if (!dominated_by_p (CDI_DOMINATORS, gimple_bb (use_stmt), top_bb))
+	    {
+	      end_imm_use_stmt_traverse (&use_iter);
+	      return false;
+	    }
+
+	  stmts.safe_push (use_stmt);
+	  if (gimple_assign_rhs_code (use_stmt) == TRUNC_DIV_EXPR)
+	    div_seen = true;
+	}
+    }
+
+  if (!div_seen)
+    return false;
+
+  /* Create libcall to internal fn DIVMOD:
+     divmod_tmp = DIVMOD (op1, op2).  */
+
+  gcall *call_stmt = gimple_build_call_internal (IFN_DIVMOD, 2, op1, op2);
+  tree res = make_temp_ssa_name (
+		build_complex_type (TREE_TYPE (op1)),
+		call_stmt, "divmod_tmp");
+  gimple_call_set_lhs (call_stmt, res);
+
+  /* Insert the call before top_stmt.  */
+  gimple_stmt_iterator top_stmt_gsi = gsi_for_stmt (top_stmt);
+  gsi_insert_before (&top_stmt_gsi, call_stmt, GSI_SAME_STMT);
+
+  widen_mul_stats.divmod_calls_inserted++;		
+
+  /* Update all statements in stmts.
+     if stmt is lhs = op1 TRUNC_DIV_EXPR op2, change to lhs = REALPART_EXPR<divmod_tmp>
+     if stmt is lhs = op1 TRUNC_MOD_EXPR op2, change to lhs = IMAGPART_EXPR<divmod_tmp>.  */
+
+  bool cfg_changed = false;
+  for (unsigned i = 0; stmts.iterate (i, &use_stmt); ++i)
+    {
+      tree new_rhs;
+
+      switch (gimple_assign_rhs_code (use_stmt))
+	{
+	  case TRUNC_DIV_EXPR:
+	    new_rhs = fold_build1 (REALPART_EXPR, TREE_TYPE (op1), res);
+	    break;
+
+	  case TRUNC_MOD_EXPR:
+	    new_rhs = fold_build1 (IMAGPART_EXPR, TREE_TYPE (op2), res);
+	    break;
+
+	  default:
+	    gcc_unreachable ();
+	}
+
+      gimple_stmt_iterator gsi = gsi_for_stmt (use_stmt);
+      gimple_assign_set_rhs_from_tree (&gsi, new_rhs);
+      update_stmt (use_stmt);
+
+      if (maybe_clean_or_replace_eh_stmt (use_stmt, use_stmt))
+	cfg_changed = true;
+    }
+
+  return cfg_changed;
+}    
 
 /* Find integer multiplications where the operands are extended from
    smaller types, and replace the MULT_EXPR with a WIDEN_MULT_EXPR
@@ -3828,6 +4056,8 @@  pass_optimize_widening_mul::execute (function *fun)
   bool cfg_changed = false;
 
   memset (&widen_mul_stats, 0, sizeof (widen_mul_stats));
+  calculate_dominance_info (CDI_DOMINATORS);
+  renumber_gimple_stmt_uids ();
 
   FOR_EACH_BB_FN (bb, fun)
     {
@@ -3861,6 +4091,10 @@  pass_optimize_widening_mul::execute (function *fun)
 		    match_uaddsub_overflow (&gsi, stmt, code);
 		  break;
 
+		case TRUNC_MOD_EXPR:
+		  cfg_changed = convert_to_divmod (as_a<gassign *> (stmt));
+		  break;
+
 		default:;
 		}
 	    }
@@ -3907,6 +4141,8 @@  pass_optimize_widening_mul::execute (function *fun)
 			    widen_mul_stats.maccs_inserted);
   statistics_counter_event (fun, "fused multiply-adds inserted",
 			    widen_mul_stats.fmas_inserted);
+  statistics_counter_event (fun, "divmod calls inserted",
+			    widen_mul_stats.divmod_calls_inserted);
 
   return cfg_changed ? TODO_cleanup_cfg : 0;
 }