[gcc r12-8892] Fix recent thinko in operand_equal_p

[Eric Botcazou <ebotcazou@gcc.gnu.org>]

https://gcc.gnu.org/g:33561e870dc48966e8c7ede46e95032279a15423

commit r12-8892-g33561e870dc48966e8c7ede46e95032279a15423
Author: Eric Botcazou <ebotcazou@adacore.com>
Date:   Fri Nov 4 11:23:12 2022 +0100

    Fix recent thinko in operand_equal_p
    
    There is a thinko in a recent improvement made to operand_equal_p where
    the code just looks at operand 2 of COMPONENT_REF, if it is present, to
    compare addresses.  That's wrong because operand 2 contains the number of
    DECL_OFFSET_ALIGN-bit-sized words so, when DECL_OFFSET_ALIGN > 8, not all
    the  bytes are included and some of them are in DECL_FIELD_BIT_OFFSET, see
    get_inner_reference for the model computation.
    
    In other words, you would need to compare operand 2 and DECL_OFFSET_ALIGN
    and DECL_FIELD_BIT_OFFSET in this situation, but I'm not sure this is worth
    the hassle in practice so the fix just removes this alternate handling.
    
    gcc/
            * fold-const.cc (operand_compare::operand_equal_p) <COMPONENT_REF>:
            Do not take into account operand 2.
            (operand_compare::hash_operand) <COMPONENT_REF>: Likewise.
    
    gcc/testsuite/
            * gnat.dg/opt99.adb: New test.
            * gnat.dg/opt99_pkg1.ads, gnat.dg/opt99_pkg1.adb: New helper.
            * gnat.dg/opt99_pkg2.ads: Likewise.

Diff:
---
 gcc/fold-const.cc                    | 18 ++++--------------
 gcc/testsuite/gnat.dg/opt99.adb      | 15 +++++++++++++++
 gcc/testsuite/gnat.dg/opt99_pkg1.adb | 10 ++++++++++
 gcc/testsuite/gnat.dg/opt99_pkg1.ads | 19 +++++++++++++++++++
 gcc/testsuite/gnat.dg/opt99_pkg2.ads | 13 +++++++++++++
 5 files changed, 61 insertions(+), 14 deletions(-)

diff --git a/gcc/fold-const.cc b/gcc/fold-const.cc
index 948e13a22d8..eec4c1820ed 100644
--- a/gcc/fold-const.cc
+++ b/gcc/fold-const.cc
@@ -3351,9 +3351,6 @@ operand_compare::operand_equal_p (const_tree arg0, const_tree arg1,
 		if (compare_address
 		    && (flags & OEP_ADDRESS_OF_SAME_FIELD) == 0)
 		  {
-		    if (TREE_OPERAND (arg0, 2)
-			|| TREE_OPERAND (arg1, 2))
-		      return OP_SAME_WITH_NULL (2);
 		    tree field0 = TREE_OPERAND (arg0, 1);
 		    tree field1 = TREE_OPERAND (arg1, 1);
 
@@ -3864,17 +3861,10 @@ operand_compare::hash_operand (const_tree t, inchash::hash &hstate,
 	      if (sflags & OEP_ADDRESS_OF)
 		{
 		  hash_operand (TREE_OPERAND (t, 0), hstate, flags);
-		  if (TREE_OPERAND (t, 2))
-		    hash_operand (TREE_OPERAND (t, 2), hstate,
-				  flags & ~OEP_ADDRESS_OF);
-		  else
-		    {
-		      tree field = TREE_OPERAND (t, 1);
-		      hash_operand (DECL_FIELD_OFFSET (field),
-				    hstate, flags & ~OEP_ADDRESS_OF);
-		      hash_operand (DECL_FIELD_BIT_OFFSET (field),
-				    hstate, flags & ~OEP_ADDRESS_OF);
-		    }
+		  hash_operand (DECL_FIELD_OFFSET (TREE_OPERAND (t, 1)),
+				hstate, flags & ~OEP_ADDRESS_OF);
+		  hash_operand (DECL_FIELD_BIT_OFFSET (TREE_OPERAND (t, 1)),
+				hstate, flags & ~OEP_ADDRESS_OF);
 		  return;
 		}
 	      break;
diff --git a/gcc/testsuite/gnat.dg/opt99.adb b/gcc/testsuite/gnat.dg/opt99.adb
new file mode 100644
index 00000000000..8805d47c122
--- /dev/null
+++ b/gcc/testsuite/gnat.dg/opt99.adb
@@ -0,0 +1,15 @@
+-- { dg-do run }
+-- { dg-options "-O" }
+
+with Opt99_Pkg1; use Opt99_Pkg1;
+
+procedure Opt99 is
+  C : constant My_Character := (D => True, C => ' ');
+  D : Derived;
+
+begin
+  Set (D, C, C);
+  if not D.C2.D then
+    raise Program_Error;
+  end if;
+end;
diff --git a/gcc/testsuite/gnat.dg/opt99_pkg1.adb b/gcc/testsuite/gnat.dg/opt99_pkg1.adb
new file mode 100644
index 00000000000..476b09c9524
--- /dev/null
+++ b/gcc/testsuite/gnat.dg/opt99_pkg1.adb
@@ -0,0 +1,10 @@
+package body Opt99_Pkg1 is
+
+  procedure Set (D: in out Derived; C1, C2 : My_Character) is
+  begin
+    D.I  := 0;
+    D.C1 := C1;
+    D.C2 := C2;
+  end;
+
+end Opt99_Pkg1;
diff --git a/gcc/testsuite/gnat.dg/opt99_pkg1.ads b/gcc/testsuite/gnat.dg/opt99_pkg1.ads
new file mode 100644
index 00000000000..3e265616d14
--- /dev/null
+++ b/gcc/testsuite/gnat.dg/opt99_pkg1.ads
@@ -0,0 +1,19 @@
+with Opt99_Pkg2;
+
+package Opt99_Pkg1 is
+
+  type My_Character (D : Boolean := False) is record
+    case D is
+      when False => null;
+      when True  => C : Character;
+    end case;
+  end record;
+
+  type Derived is new Opt99_Pkg2.Root with record
+    I : Integer;
+    C1, C2 : My_Character;
+  end record;
+
+  procedure Set (D: in out Derived; C1, C2 : My_Character);
+
+end Opt99_Pkg1;
diff --git a/gcc/testsuite/gnat.dg/opt99_pkg2.ads b/gcc/testsuite/gnat.dg/opt99_pkg2.ads
new file mode 100644
index 00000000000..09aaff14e01
--- /dev/null
+++ b/gcc/testsuite/gnat.dg/opt99_pkg2.ads
@@ -0,0 +1,13 @@
+package Opt99_Pkg2 is
+
+  function Get_Max return Positive is (4);
+
+  C : constant Positive := Get_Max;
+
+  type Arr is array (1 .. C) of Integer;
+
+  type Root is tagged record
+    Data : Arr;
+  end record;
+
+end Opt99_Pkg2;