[gcc r15-10604] Ada: Fix ICE when comparing reduction expression with integer constant

[Eric Botcazou]

https://gcc.gnu.org/g:043ed7e185958510067698be29a549dff30fe326

commit r15-10604-g043ed7e185958510067698be29a549dff30fe326
Author: Eric Botcazou <ebotcazou@adacore.com>
Date:   Tue Dec 16 00:34:31 2025 +0100

    Ada: Fix ICE when comparing reduction expression with integer constant
    
    This a regression present on the mainline, 15 and 14 branches: the compiler
    aborts on the comparison of the result of a reduction expression, whose
    prefix is an aggregate, and an integer constant, because of a type mismatch
    created by the resolution of the reduction expression, which unduly forces
    Integer on the reduction expression.
    
    gcc/ada/
            PR ada/123138
            * exp_attr.adb (Expand_N_Attribute_Reference) <Attribute_Reduce>:
            Override a universal numeric type only if the prefix is not an
            aggregate.
    
    gcc/testsuite/
            * gnat.dg/reduce4.adb: New test.
            * gnat.dg/reduce5.adb: Likewise.

Diff:
---
 gcc/ada/exp_attr.adb              | 11 +++++------
 gcc/testsuite/gnat.dg/reduce4.adb |  9 +++++++++
 gcc/testsuite/gnat.dg/reduce5.adb | 36 ++++++++++++++++++++++++++++++++++++
 3 files changed, 50 insertions(+), 6 deletions(-)

diff --git a/gcc/ada/exp_attr.adb b/gcc/ada/exp_attr.adb
index 1eff20d14aca..66ef1919576c 100644
--- a/gcc/ada/exp_attr.adb
+++ b/gcc/ada/exp_attr.adb
@@ -6368,14 +6368,13 @@ package body Exp_Attr is
                   Accum_Typ := Etype (N);
                end if;
 
-               --  Try to cope with wrong E1 when Etype (N) doesn't help
+               --  If Accum_Typ is a universal numeric type and the prefix
+               --  is not an aggregate, use its component type in order to
+               --  avoid resolution problems later on.
+
                if Is_Universal_Numeric_Type (Accum_Typ) then
-                  if Is_Array_Type (Etype (Prefix (N))) then
+                  if Nkind (Prefix (N)) /= N_Aggregate then
                      Accum_Typ := Component_Type (Etype (Prefix (N)));
-                  else
-                     --  Further hackery can be added here when there is a
-                     --  demonstrated need.
-                     null;
                   end if;
                end if;
 
diff --git a/gcc/testsuite/gnat.dg/reduce4.adb b/gcc/testsuite/gnat.dg/reduce4.adb
new file mode 100644
index 000000000000..ac27b7c0cc45
--- /dev/null
+++ b/gcc/testsuite/gnat.dg/reduce4.adb
@@ -0,0 +1,9 @@
+-- { dg-do compile }
+-- { dg-options "-gnat2022" }
+
+procedure Reduce4 (S : String) is
+begin
+  if [for E of S => 1]'Reduce ("+", 0) = 3 then
+    null;
+  end if;
+end;
diff --git a/gcc/testsuite/gnat.dg/reduce5.adb b/gcc/testsuite/gnat.dg/reduce5.adb
new file mode 100644
index 000000000000..e377f6e25486
--- /dev/null
+++ b/gcc/testsuite/gnat.dg/reduce5.adb
@@ -0,0 +1,36 @@
+-- { dg-do compile }
+-- { dg-options "-gnat2022" }
+
+with Ada.Text_IO; use Ada.Text_IO;
+
+procedure Reduce5 is
+   subtype Chunk_Number is Natural range 1 .. 8;
+   Grid  : array (1 .. 80, 1 .. 100) of Boolean := (others => (others => False));
+   Partial_Sum, Partial_Max : array (Chunk_Number) of Natural := (others => 0);
+   Partial_Min              : array (Chunk_Number) of Natural := (others => Natural'Last);
+
+begin
+   for I in Grid'Range (1) loop
+      Grid (I, 1) := (for all J in Grid'Range (2) => Grid (I, J) = True);
+   end loop;
+
+   for I in Grid'Range (1) loop
+      declare
+         True_Count : constant Natural :=
+           [for J in Grid'Range(2) => (if Grid (I, J) then 1 else 0)]'Reduce("+",0);
+      begin
+         Partial_Sum (I) := @ + True_Count;
+         Partial_Min (I) := Natural'Min (@, True_Count);
+         Partial_Max (I) := Natural'Max (@, True_Count);
+      end;
+   end loop;
+
+  Put_Line ("Total=" & Natural'Image (Partial_Sum'Reduce ("+", 0)) &
+            ", Min=" & Natural'Image (Partial_Min'Reduce(Natural'Min, Natural'Last)) &
+            ", Max=" & Natural'Image (Partial_Max'Reduce(Natural'Max, 0)));
+
+  Put_Line ("Total=" & Partial_Sum'Reduce ("+", 0)'Image &
+            ", Min=" & Partial_Min'Reduce(Natural'Min, Natural'Last)'Image &
+            ", Max=" & Partial_Max'Reduce(Natural'Max, 0)'Image);
+
+end;