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https://issues.apache.org/jira/browse/STDCXX-904?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12594463#action_12594463
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Martin Sebor commented on STDCXX-904:
-------------------------------------
Dennis' response:
------- Original Message --------
Subject: Re: bogus warning 20206 on a memcpy-like loop with +O2
Date: Mon, 5 May 2008 19:18:40 -0700 (PDT)
From: Dennis Handly <dhandly AT cup DOT hp DOT com>
To: acxx AT cup DOT hp DOT com, sebor AT roguewave DOT com
>From: Martin Sebor <sebor AT roguewave DOT com>
>Here's a new test case for an apparent aCC bug reduced from our test suite.
It seems directly related to the "%" operator. Using "i" or a constant
makes it go away.
You can also duplicate this if the class B is moved to file scope.
The only way I found to make the warning go away is to use signed for this
for-loop:
{{for (int i = 3; i != n - 1; --i)}}
Not sure why since both should wrap around. If "n" and "i" are both ints
we get a different range message.
{noformat}
struct B {
char x[4];
void bar(unsigned n) {
for (unsigned i = 3; i != n - 1; --i)
x[i] = x[i - n];
}
} x;
for (unsigned i = 0; i != 1; ++i) {
x.bar(i % 4);
}
{noformat}
> [HP aCC 6.16] bogus cadvise warning #20206 in optimized code
> ------------------------------------------------------------
>
> Key: STDCXX-904
> URL: https://issues.apache.org/jira/browse/STDCXX-904
> Project: C++ Standard Library
> Issue Type: Bug
> Components: External
> Affects Versions: 4.2.1
> Environment: $ uname -sr && aCC -V
> HP-UX B.11.31
> aCC: HP C/aC++ B3910B A.06.16 [Nov 26 2007]
> Reporter: Travis Vitek
>
> This is a simplified version of 23.bitset.cpp that shows a bogus out of bound
> access cadvise warning.
> {noformat}
> void __rw_bitset (unsigned*, unsigned, const char*, unsigned, unsigned,
> unsigned);
> template <unsigned _Size>
> class bitset
> {
> unsigned bits_ [1];
> public:
> bitset (const char *__str, unsigned __pos, unsigned __n) {
> __rw_bitset (bits_, _Size, __str, 0, __pos, __n);
> }
> };
> template <unsigned _Size>
> struct test_set
> {
> char bits_ [_Size + 1]; // includes a null terminator
> test_set () {
> for (unsigned i = 0; i != _Size; ++i)
> bits_ [i] = '0';
> bits_ [_Size] = '\0';
> }
> test_set& operator>>= (unsigned n) {
> for (unsigned i = _Size - 1; i != n - 1; --i)
> bits_ [i] = bits_ [i - n];
> for (unsigned j = n; j != 0; )
> bits_ [--j] = '0';
> return *this;
> }
> };
> template <unsigned _Size>
> void run_test ()
> {
> test_set<_Size> ts0;
> const unsigned M = _Size + 1;
> for (unsigned i = 0; i != 1; ++i) {
> const unsigned n = i % M;
>
> const test_set<_Size> ts1 = (ts0 >>= n);
> (void)&ts1;
> const bitset<_Size> bs0 (ts0.bits_, 0, _Size);
> }
> }
> int main (int argc, char *argv[])
> {
> run_test<31>();
> return 0;
> }
> {noformat}
> The result of compiling this code with -O2 is...
> {noformat}
> aCC -c -mt \
> -I/amd/devco/vitek/stdcxx/4.2.x/include \
> -I/amd/devco/vitek/stdcxx/4.2.x/build/include \
> -I/amd/devco/vitek/stdcxx/4.2.x/tests/include \
> -AA +O2 +DD64 +w \
> +W392,655,684,818,819,849 \
> +W2193,2236,2261,2340,2401,2487 \
> +W4227,4229,4231,4235,4237,4249 \
> +W4255,4272,4284,4285,4286,4296,4297 \
> +W3348 u.cpp
> "u.cpp", line 29, procedure main: warning #20206-D: Out of bound access \
> (In expression "memmove(&(&ts0)->bits_[30]+1 - (31 - n),&(&ts0)->bits_[(30
> - n)]+1 - (31 - n),31 - n)", &(&ts0)->bits_[30]+1 - (31 - n) \
> (type: char [32]) (defined by (&ts0)->bits_) has byte range [0 .. 31],
> writing byte range [0 .. 60].)
> {noformat}
> The code compiles without warning if the optimization level is reduced to -O1.
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