From 4e1a215870a4194c9ca884ef838103c094aa38c8 Mon Sep 17 00:00:00 2001
From: Eric Botcazou <ebotcazou@adacore.com>
Date: Wed, 11 Nov 2020 15:08:16 +0100
Subject: [PATCH] Fix biased integer arithmetic
The Ada compiler uses a biased representation when a size clause reserves
fewer bits than normal either for the lower or for the upper bound.
gcc/ada/ChangeLog:
* gcc-interface/trans.c (build_binary_op_trapv): Convert operands
to the result type before doing generic overflow checking.
gcc/testsuite/ChangeLog:
* gnat.dg/bias2.adb: New test.
---
gcc/ada/gcc-interface/trans.c | 5 +++++
gcc/testsuite/gnat.dg/bias2.adb | 33 +++++++++++++++++++++++++++++++++
2 files changed, 38 insertions(+)
create mode 100644 gcc/testsuite/gnat.dg/bias2.adb
diff --git a/gcc/ada/gcc-interface/trans.c b/gcc/ada/gcc-interface/trans.c
index 065fcd2f956e..7be8463d32b3 100644
--- a/gcc/ada/gcc-interface/trans.c
+++ b/gcc/ada/gcc-interface/trans.c
@@ -9361,6 +9361,11 @@ build_binary_op_trapv (enum tree_code code, tree gnu_type, tree left,
/* If no operand is a constant, we use the generic implementation. */
if (TREE_CODE (lhs) != INTEGER_CST && TREE_CODE (rhs) != INTEGER_CST)
{
+ /* First convert the operands to the result type like build_binary_op.
+ This is where the bias is made explicit for biased types. */
+ lhs = convert (gnu_type, lhs);
+ rhs = convert (gnu_type, rhs);
+
/* Never inline a 64-bit mult for a 32-bit target, it's way too long. */
if (code == MULT_EXPR && precision == 64 && BITS_PER_WORD < 64)
{
diff --git a/gcc/testsuite/gnat.dg/bias2.adb b/gcc/testsuite/gnat.dg/bias2.adb
new file mode 100644
index 000000000000..a32e9a337ad7
--- /dev/null
+++ b/gcc/testsuite/gnat.dg/bias2.adb
@@ -0,0 +1,33 @@
+-- { dg-do run }
+
+procedure Bias2 is
+
+ type Biased_T is range 1 .. 2 ** 6;
+ for Biased_T'Size use 6; -- { dg-warning "biased representation" }
+ X, Y : Biased_T;
+
+begin
+ X := 1;
+ Y := 1;
+ if X + Y /= 2 then
+ raise Program_Error;
+ end if;
+
+ X := 2;
+ Y := 1;
+ if X - Y /= 1 then
+ raise Program_Error;
+ end if;
+
+ X := 2;
+ Y := 3;
+ if X * Y /= 6 then
+ raise Program_Error;
+ end if;
+
+ X := 24;
+ Y := 3;
+ if X / Y /= 8 then
+ raise Program_Error;
+ end if;
+end;
--
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