Re: [PATCH][2 of 2] RTL expansion for zero sign extension elimination with VRP

[Kugan <kugan.vivekanandarajah@linaro.org>]

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Hi Eric,

Thanks for reviewing the patch.

On 01/07/13 18:51, Eric Botcazou wrote:
> [Sorry for the delay]
>
>> For example, when an expression is evaluated and it's value is assigned
>> to variable of type short, the generated RTL would look something like
>> the following.
>>
>> (set (reg:SI 110)
>>                    (zero_extend:SI (subreg:HI (reg:SI 117) 0)))
>>
>> However, if during value range propagation, if we can say for certain
>> that the value of the expression which is present in register 117 is
>> within the limits of short and there is no sign conversion, we do not
>> need to perform the subreg and zero_extend; instead we can generate the
>> following RTl.
>>
>> (set (reg:SI 110)
>>                    (reg:SI 117)))
>>
>> Same could be done for other assign statements.
>
> The idea looks interesting.  Some remarks:
>
>> +2013-06-03  Kugan Vivekanandarajah  <kuganv@linaro.org>
>> +
>> +	* gcc/dojump.c (do_compare_and_jump): generates rtl without
>> +	zero/sign extension if redundant.
>> +	* gcc/cfgexpand.c (expand_gimple_stmt_1): Likewise.
>> +	* gcc/gimple.c (gimple_assign_is_zero_sign_ext_redundant) : New
>> +	function.
>> +	* gcc/gimple.h (gimple_assign_is_zero_sign_ext_redundant) : New
>> +	function definition.
>
> No gcc/ prefix in entries for gcc/ChangeLog.  "Generate RTL without..."
>
I have now changed it to.

--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,3 +1,13 @@
+2013-08-14  Kugan Vivekanandarajah  <kuganv@linaro.org>
+
+	* dojump.c (do_compare_and_jump): Generate rtl without
+	zero/sign extension if redundant.
+	* cfgexpand.c (expand_gimple_stmt_1): Likewise.
+	* gimple.c (gimple_assign_is_zero_sign_ext_redundant) : New
+	function.
+	* gimple.h (gimple_assign_is_zero_sign_ext_redundant) : New
+	function definition.
+
  2013-08-09  Jan Hubicka  <jh@suse.cz>

  	* cgraph.c (cgraph_create_edge_1): Clear speculative flag.

>
> +            /* If the value in SUBREG of temp fits that SUBREG (does not
> +               overflow) and is assigned to target SUBREG of the same mode
> +               without sign convertion, we can skip the SUBREG
> +               and extension.  */
> +            else if (promoted
> +                     && gimple_assign_is_zero_sign_ext_redundant (stmt)
> +                     && (GET_CODE (temp) == SUBREG)
> +                     && (GET_MODE (target) == GET_MODE (temp))
> +                     && (GET_MODE (SUBREG_REG (target))
> +                         == GET_MODE (SUBREG_REG (temp))))
> +	      emit_move_insn (SUBREG_REG (target), SUBREG_REG (temp));
>   	    else if (promoted)
>   	      {
>   		int unsignedp = SUBREG_PROMOTED_UNSIGNED_P (target);
>
> Can we relax the strict mode equality here?  This change augments the same
> transformation applied to the RHS when it is also a SUBREG_PROMOTED_VAR_P at
> the beginning of convert_move, but the condition on the mode is less strict in
> the latter case, so maybe it can serve as a model here.
>

I have now changed it based on convert_move to
+            else if (promoted
+                     && gimple_assign_is_zero_sign_ext_redundant (stmt)
+                     && (GET_CODE (temp) == SUBREG)
+                     && (GET_MODE_PRECISION (GET_MODE (SUBREG_REG (temp)))
+	                 >= GET_MODE_PRECISION (GET_MODE (target)))
+                     && (GET_MODE (SUBREG_REG (target))
+                         == GET_MODE (SUBREG_REG (temp))))
+              {

Is this what you wanted me to do.
>
> +  /* Is zero/sign extension redundant as per VRP.  */
> +  bool op0_ext_redundant = false;
> +  bool op1_ext_redundant = false;
> +
> +  /* If promoted and the value in SUBREG of op0 fits (does not overflow),
> +     it is a candidate for extension elimination.  */
> +  if (GET_CODE (op0) == SUBREG && SUBREG_PROMOTED_VAR_P (op0))
> +    op0_ext_redundant =
> +      gimple_assign_is_zero_sign_ext_redundant (SSA_NAME_DEF_STMT (treeop0));
> +
> +  /* If promoted and the value in SUBREG of op1 fits (does not overflow),
> +     it is a candidate for extension elimination.  */
> +  if (GET_CODE (op1) == SUBREG && SUBREG_PROMOTED_VAR_P (op1))
> +    op1_ext_redundant =
> +      gimple_assign_is_zero_sign_ext_redundant (SSA_NAME_DEF_STMT (treeop1));
>
> Are the gimple_assign_is_zero_sign_ext_redundant checks necessary here?
> When set on a SUBREG, SUBREG_PROMOTED_VAR_P guarantees that SUBREG_REG is
> always properly extended (otherwise it's a bug) so don't you just need to
> compare SUBREG_PROMOTED_UNSIGNED_SET?  See do_jump for an existing case.
>
I am sorry I donÂ’t think I understood you here. How would I know that 
extension is redundant without calling 
gimple_assign_is_zero_sign_ext_redundant ? Could you please elaborate.

>
> +  /* If zero/sign extension is redundant, generate RTL
> +     for operands without zero/sign extension.  */
> +  if ((op0_ext_redundant || TREE_CODE (treeop0) == INTEGER_CST)
> +      && (op1_ext_redundant || TREE_CODE (treeop1) == INTEGER_CST))
>
> Don't you need to be careful with the INTEGER_CSTs here?  The CONST_INTs are
> always sign-extended in RTL so 0x80 is always represented by (const_int -128)
> in QImode, whatever the signedness.  If SUBREG_PROMOTED_UNSIGNED_SET is true,
> then comparing in QImode and comparing in e.g. SImode wouldn't be equivalent.
>

I have changed this.

I have attached the modified patch your your review.

Thanks,
Kugan

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diff --git a/gcc/cfgexpand.c b/gcc/cfgexpand.c
index a7d9170..8f08cc2 100644
--- a/gcc/cfgexpand.c
+++ b/gcc/cfgexpand.c
@@ -2311,6 +2311,20 @@ expand_gimple_stmt_1 (gimple stmt)
 
 	    if (temp == target)
 	      ;
+            /* If the value in SUBREG of temp fits that SUBREG (does not
+               overflow) and is assigned to target SUBREG of the same mode
+               without sign convertion, we can skip the SUBREG
+               and extension.  */
+            else if (promoted
+                     && gimple_assign_is_zero_sign_ext_redundant (stmt)
+                     && (GET_CODE (temp) == SUBREG)
+                     && (GET_MODE_PRECISION (GET_MODE (SUBREG_REG (temp)))
+	                 >= GET_MODE_PRECISION (GET_MODE (target)))
+                     && (GET_MODE (SUBREG_REG (target))
+                         == GET_MODE (SUBREG_REG (temp))))
+              {
+	        emit_move_insn (SUBREG_REG (target), SUBREG_REG (temp));
+              }
 	    else if (promoted)
 	      {
 		int unsignedp = SUBREG_PROMOTED_UNSIGNED_P (target);
diff --git a/gcc/dojump.c b/gcc/dojump.c
index 3f04eac..639d38f 100644
--- a/gcc/dojump.c
+++ b/gcc/dojump.c
@@ -34,6 +34,7 @@ along with GCC; see the file COPYING3.  If not see
 #include "ggc.h"
 #include "basic-block.h"
 #include "tm_p.h"
+#include "gimple.h"
 
 static bool prefer_and_bit_test (enum machine_mode, int);
 static void do_jump_by_parts_greater (tree, tree, int, rtx, rtx, int);
@@ -1108,6 +1109,61 @@ do_compare_and_jump (tree treeop0, tree treeop1, enum rtx_code signed_code,
 
   type = TREE_TYPE (treeop0);
   mode = TYPE_MODE (type);
+
+  /* Is zero/sign extension redundant as per VRP.  */
+  bool op0_ext_redundant = false;
+  bool op1_ext_redundant = false;
+
+  /* If promoted and the value in SUBREG of op0 fits (does not overflow),
+     it is a candidate for extension elimination.  */
+  if (GET_CODE (op0) == SUBREG && SUBREG_PROMOTED_VAR_P (op0))
+    op0_ext_redundant =
+      gimple_assign_is_zero_sign_ext_redundant (SSA_NAME_DEF_STMT (treeop0));
+
+  /* If promoted and the value in SUBREG of op1 fits (does not overflow),
+     it is a candidate for extension elimination.  */
+  if (GET_CODE (op1) == SUBREG && SUBREG_PROMOTED_VAR_P (op1))
+    op1_ext_redundant =
+      gimple_assign_is_zero_sign_ext_redundant (SSA_NAME_DEF_STMT (treeop1));
+
+  /* If zero/sign extension is redundant, generate RTL
+     for operands without zero/sign extension.  */
+  if ((op0_ext_redundant || TREE_CODE (treeop0) == INTEGER_CST)
+      && (op1_ext_redundant || TREE_CODE (treeop1) == INTEGER_CST))
+    {
+      if ((TREE_CODE (treeop1) == INTEGER_CST)
+          && (!mode_signbit_p (GET_MODE (op0), op1)))
+        {
+          /* First operand is constant.  */
+          rtx new_op0 = gen_reg_rtx (GET_MODE (SUBREG_REG (op0)));
+          emit_move_insn (new_op0, SUBREG_REG (op0));
+          op0 = new_op0;
+        }
+      else if ((TREE_CODE (treeop0) == INTEGER_CST)
+              && (!mode_signbit_p (GET_MODE (op1), op0)))
+        {
+          /* Other operand is constant.  */
+          rtx new_op1 = gen_reg_rtx (GET_MODE (SUBREG_REG (op1)));
+
+          emit_move_insn (new_op1, SUBREG_REG (op1));
+          op1 = new_op1;
+        }
+      /* If both the comapre registers fits SUBREG and of the same mode.  */
+      else if ((TREE_CODE (treeop0) != INTEGER_CST)
+              && (TREE_CODE (treeop1) != INTEGER_CST)
+              && (GET_MODE (op0) == GET_MODE (op1))
+              && (GET_MODE (SUBREG_REG (op0)) == GET_MODE (SUBREG_REG (op1))))
+        {
+          rtx new_op0 = gen_reg_rtx (GET_MODE (SUBREG_REG (op0)));
+          rtx new_op1 = gen_reg_rtx (GET_MODE (SUBREG_REG (op1)));
+
+          emit_move_insn (new_op0, SUBREG_REG (op0));
+          emit_move_insn (new_op1, SUBREG_REG (op1));
+          op0 = new_op0;
+          op1 = new_op1;
+        }
+    }
+
   if (TREE_CODE (treeop0) == INTEGER_CST
       && (TREE_CODE (treeop1) != INTEGER_CST
           || (GET_MODE_BITSIZE (mode)
diff --git a/gcc/gimple.c b/gcc/gimple.c
index f507419..17d90ee 100644
--- a/gcc/gimple.c
+++ b/gcc/gimple.c
@@ -200,6 +200,75 @@ gimple_call_reset_alias_info (gimple s)
     pt_solution_reset (gimple_call_clobber_set (s));
 }
 
+
+/* process gimple assign stmts and see if the sign/zero extensions are
+   redundant.  i.e.  if an assignment gimple statement has RHS expression
+   value that can fit in LHS type, truncation is redundant.  Zero/sign
+   extensions in this case can be removed.  */
+bool
+gimple_assign_is_zero_sign_ext_redundant (gimple stmt)
+{
+  double_int type_min, type_max;
+  tree int_val = NULL_TREE;
+  range_info_def *ri;
+
+  /* skip if not assign stmt.  */
+  if (!is_gimple_assign (stmt))
+    return false;
+
+  tree lhs = gimple_assign_lhs (stmt);
+
+  /* We can remove extension only for non-pointer and integral stmts.  */
+  if (!INTEGRAL_TYPE_P (TREE_TYPE (lhs))
+      || POINTER_TYPE_P (TREE_TYPE (lhs)))
+    return false;
+
+  type_max = tree_to_double_int (TYPE_MAX_VALUE (TREE_TYPE (lhs)));
+  type_min = tree_to_double_int (TYPE_MIN_VALUE (TREE_TYPE (lhs)));
+
+  /* For binary expressions, if one of the argument is constant and is
+     larger than tne signed maximum, it can be intepreted as nagative
+     and sign extended.  This could lead to problems so return false in
+     this case.  */
+  if (TREE_CODE_CLASS (gimple_assign_rhs_code (stmt)) == tcc_binary)
+    {
+      tree rhs1 = gimple_assign_rhs1 (stmt);
+      tree rhs2 = gimple_assign_rhs2 (stmt);
+
+      if (TREE_CODE (rhs1) == INTEGER_CST)
+        int_val = rhs1;
+      else if (TREE_CODE (rhs2) == INTEGER_CST)
+        int_val = rhs2;
+
+      if (int_val != NULL_TREE)
+        {
+          tree max = TYPE_MIN_VALUE (TREE_TYPE (lhs));
+
+          /* if type is unsigned, get the max for signed equivalent.  */
+         if (!INT_CST_LT (TYPE_MIN_VALUE (TREE_TYPE (lhs)), integer_zero_node))
+            max = int_const_binop (RSHIFT_EXPR,
+                                    max, build_int_cst (TREE_TYPE (max), 1));
+          if (!INT_CST_LT (int_val, max))
+            return false;
+        }
+    }
+
+  /* Get the value range.  */
+  ri = SSA_NAME_RANGE_INFO (lhs);
+
+  /* Check if value range is valid.  */
+  if (!ri || !ri->valid || !ri->vr_range)
+    return false;
+
+  /* Value range fits type.  */
+  if (ri->max.scmp (type_max) != 1
+      && (type_min.scmp (ri->min) != 1))
+    return true;
+
+  return false;
+}
+
+
 /* Helper for gimple_build_call, gimple_build_call_valist,
    gimple_build_call_vec and gimple_build_call_from_tree.  Build the basic
    components of a GIMPLE_CALL statement to function FN with NARGS
diff --git a/gcc/gimple.h b/gcc/gimple.h
index 8ae07c9..769e7e4 100644
--- a/gcc/gimple.h
+++ b/gcc/gimple.h
@@ -829,6 +829,7 @@ int gimple_call_flags (const_gimple);
 int gimple_call_return_flags (const_gimple);
 int gimple_call_arg_flags (const_gimple, unsigned);
 void gimple_call_reset_alias_info (gimple);
+bool gimple_assign_is_zero_sign_ext_redundant (gimple);
 bool gimple_assign_copy_p (gimple);
 bool gimple_assign_ssa_name_copy_p (gimple);
 bool gimple_assign_unary_nop_p (gimple);