https://gcc.gnu.org/bugzilla/show_bug.cgi?id=93233
Bug ID: 93233
Summary: No warning for possibly uninitialised return
Product: gcc
Version: 9.2.1
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: ada
Assignee: unassigned at gcc dot gnu.org
Reporter: chris at amtiskaw dot net
Target Milestone: ---
Created attachment 47637
--> https://gcc.gnu.org/bugzilla/attachment.cgi?id=47637&action=edit
Test case using normal and extended return syntax.
Hi,
I'm learning Ada and was surprised to find that the compiler
failed to issue a warning when a variable used as the return
value of a (simple) function was only conditionally initialised.
I discovered this while investigating a bug in a function that
used the extended return syntax, so I constructed the following
test case which tries both normal and extended returns:
with Ada.Text_IO; use Ada.Text_IO;
procedure Returns is
function Normal(X: in Integer) return Boolean is
Result: Boolean;
begin
if X < 0 then
Result := true;
end if;
return Result;
end Normal;
function Extended(X: in Integer) return Boolean is
begin
return Result : Boolean do
if X < 0 then
Result := true;
end if;
end return;
end Extended;
begin
Put_Line("Normal(0): " & Normal(0)'Image);
Put_Line("Normal(-1): " & Normal(-1)'Image);
Put_Line("Extended(0): " & Extended(0)'Image);
Put_Line("Extended(-1): " & Extended(-1)'Image);
end Returns;
Compiling using gnatmake succeeds with no warnings about the
potentially uninitialised `Result` from the compiler:
$ gnatmake -v -Wall -gnatwa returns.adb
GNATMAKE 9.2.1 20190827 (Red Hat 9.2.1-1)
Copyright (C) 1992-2019, Free Software Foundation, Inc.
"returns.ali" being checked ...
-> "returns.ali" missing.
gcc -c -Wall -gnatwa returns.adb
End of compilation
gnatbind -x returns.ali
gnatlink returns.ali
Running the generated executable gives unpredictable results:
$ ./returns
Normal(0): TRUE
Normal(-1): TRUE
Extended(0): FALSE
Extended(-1): TRUE
$ ./returns
Normal(0): FALSE
Normal(-1): TRUE
Extended(0): FALSE
Extended(-1): TRUE
I've tried both gcc-gnat 9.2.1 from Fedora 31, and the latest GNAT CE from
Adacore with the same results (no warnings).
------------------------------------------------
Platform details - up-to-date Fedora 31, x86_64:
GNAT 9.2.1 20190827 (Red Hat 9.2.1-1)
Using built-in specs.
COLLECT_GCC=gcc
COLLECT_LTO_WRAPPER=/usr/libexec/gcc/x86_64-redhat-linux/9/lto-wrapper
OFFLOAD_TARGET_NAMES=nvptx-none
OFFLOAD_TARGET_DEFAULT=1
Target: x86_64-redhat-linux
Configured with: ../configure --enable-bootstrap
--enable-languages=c,c++,fortran,objc,obj-c++,ada,go,d,lto --prefix=/usr
--mandir=/usr/share/man --infodir=/usr/share/info
--with-bugurl=http://bugzilla.redhat.com/bugzilla --enable-shared
--enable-threads=posix --enable-checking=release --enable-multilib
--with-system-zlib --enable-__cxa_atexit --disable-libunwind-exceptions
--enable-gnu-unique-object --enable-linker-build-id
--with-gcc-major-version-only --with-linker-hash-style=gnu --enable-plugin
--enable-initfini-array --with-isl --enable-offload-targets=nvptx-none
--without-cuda-driver --enable-gnu-indirect-function --enable-cet
--with-tune=generic --with-arch_32=i686 --build=x86_64-redhat-linux
Thread model: posix
gcc version 9.2.1 20190827 (Red Hat 9.2.1-1) (GCC)
