[gcc r13-251] [Ada] Optimize nonstandard boolean conversions

[Pierre-Marie de Rodat <pmderodat@gcc.gnu.org>]

https://gcc.gnu.org/g:bf687b8085403b94209269e15491f286644ec10b

commit r13-251-gbf687b8085403b94209269e15491f286644ec10b
Author: Alexandre Oliva <oliva@adacore.com>
Date:   Wed Dec 29 04:10:46 2021 -0300

    [Ada] Optimize nonstandard boolean conversions
    
    This patch improves the generated code for nonstandard boolean types.
    
    One of the improvements extends the code that avoids converting back
    to the nonstandard boolean type an expression computed as standard
    boolean, when it will be converted to a(nother) nonstandard boolean
    type.
    
    The other improvement involves using the literal representation
    constants in an If_Expression instead of dereferencing the T'Val array
    when converting to a (nonstandard) boolean type. Avoiding the array
    dereference enables the compiler middle-end to propagate the constants
    and perform optimizations based on them, to the point of obviating the
    improvement above.
    
    Unfortunately, the code generated with this alternate expansion tends
    to be slightly larger if it turns out to not enable any further
    optimization, though it's most certainly faster, especially on targets
    with conditional moves, more so if "store flag" is slow, as on x86.
    Still, the array dereference is more straightforward and shorter, so
    I've arranged for this alternate expansion to be used only when
    optimizing for speed.
    
    gcc/ada/
    
            * exp_util.adb (Adjust_Result_Type): Leave result in
            Standard.Boolean if it's going to be converted to another
            boolean type.
            * exp_ch4.adb (Expand_N_Type_Conversion): When optimizing,
            convert to nonstandard booleans with an if_expression with
            boolean literals.

Diff:
---
 gcc/ada/exp_ch4.adb  | 37 +++++++++++++++++++++++++++----------
 gcc/ada/exp_util.adb |  3 +++
 2 files changed, 30 insertions(+), 10 deletions(-)

diff --git a/gcc/ada/exp_ch4.adb b/gcc/ada/exp_ch4.adb
index 98ce797be68..f827fb037f9 100644
--- a/gcc/ada/exp_ch4.adb
+++ b/gcc/ada/exp_ch4.adb
@@ -12757,18 +12757,35 @@ package body Exp_Ch4 is
          if not Has_Compatible_Representation (Target_Type, Operand_Type)
            and then not Conversion_OK (N)
          then
+            if Optimization_Level > 0
+              and then Is_Boolean_Type (Target_Type)
+            then
+               --  Convert x(y) to (if y then x'(True) else x'(False)).
+               --  Use literals, instead of indexing x'val, to enable
+               --  further optimizations in the middle-end.
 
-            --  Convert: x(y) to x'val (ytyp'pos (y))
+               Rewrite (N,
+                 Make_If_Expression (Loc,
+                   Expressions => New_List (
+                     Operand,
+                     Convert_To (Target_Type,
+                                 New_Occurrence_Of (Standard_True, Loc)),
+                     Convert_To (Target_Type,
+                                 New_Occurrence_Of (Standard_False, Loc)))));
 
-            Rewrite (N,
-              Make_Attribute_Reference (Loc,
-                Prefix         => New_Occurrence_Of (Target_Type, Loc),
-                Attribute_Name => Name_Val,
-                Expressions    => New_List (
-                  Make_Attribute_Reference (Loc,
-                    Prefix         => New_Occurrence_Of (Operand_Type, Loc),
-                    Attribute_Name => Name_Pos,
-                    Expressions    => New_List (Operand)))));
+            else
+               --  Convert: x(y) to x'val (ytyp'pos (y))
+
+               Rewrite (N,
+                 Make_Attribute_Reference (Loc,
+                   Prefix         => New_Occurrence_Of (Target_Type, Loc),
+                   Attribute_Name => Name_Val,
+                   Expressions    => New_List (
+                     Make_Attribute_Reference (Loc,
+                       Prefix         => New_Occurrence_Of (Operand_Type, Loc),
+                       Attribute_Name => Name_Pos,
+                       Expressions    => New_List (Operand)))));
+            end if;
 
             Analyze_And_Resolve (N, Target_Type);
          end if;
diff --git a/gcc/ada/exp_util.adb b/gcc/ada/exp_util.adb
index c28723c35e0..795c1b082f7 100644
--- a/gcc/ada/exp_util.adb
+++ b/gcc/ada/exp_util.adb
@@ -424,6 +424,9 @@ package body Exp_Util is
             elsif     KP in N_Op_Boolean
               or else KP in N_Short_Circuit
               or else KP = N_Op_Not
+              or else (KP in N_Type_Conversion
+                           | N_Unchecked_Type_Conversion
+                        and then Is_Boolean_Type (Etype (Parent (N))))
             then
                return;