Bug 39974 - [4.5 regression] Bogus "array subscript is below array bounds" warning in compiler generated code
Summary: [4.5 regression] Bogus "array subscript is below array bounds" warning in com...
Status: RESOLVED FIXED
Alias: None
Product: gcc
Classification: Unclassified
Component: tree-optimization (show other bugs)
Version: 4.5.0
: P2 normal
Target Milestone: 4.5.0
Assignee: Not yet assigned to anyone
URL:
Keywords: diagnostic
Depends on:
Blocks:
 
Reported: 2009-04-30 09:15 UTC by Volker Reichelt
Modified: 2009-09-28 20:11 UTC (History)
1 user (show)

See Also:
Host:
Target:
Build:
Known to work:
Known to fail:
Last reconfirmed: 2009-06-22 00:43:26

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Description Volker Reichelt 2009-04-30 09:15:12 UTC 
The following code snippet produces a bogus warning when compiled with
"-O2 -Wall" on trunk:

bug.cc: In function 'void _Z41__static_initialization_and_destruction_0ii.clone.0()':
bug.cc:3: warning: array subscript is below array bounds
bug.cc:3: warning: array subscript is below array bounds
bug.cc:3: warning: array subscript is below array bounds

Maybe the warning indicates a code generation bug.

Interestingly, the second array must contain at least 42 elements ;-)

==================================================================
#include<string>

std::string x[2][3] = { { "", "", "" }, { "", "", "" } };

struct A
{
  A(int);
};

struct B
{
  A a1, a2, a3, a4, a5, a6;
};

B b[42] =
{
  { 0, 0, 0, 0, 0, 0 },
  { 0, 0, 0, 0, 0, 0 },
  { 0, 0, 0, 0, 0, 0 },
  { 0, 0, 0, 0, 0, 0 },
  { 0, 0, 0, 0, 0, 0 },
  { 0, 0, 0, 0, 0, 0 },
  { 0, 0, 0, 0, 0, 0 },
  { 0, 0, 0, 0, 0, 0 },
  { 0, 0, 0, 0, 0, 0 },
  { 0, 0, 0, 0, 0, 0 },
  { 0, 0, 0, 0, 0, 0 },
  { 0, 0, 0, 0, 0, 0 },
  { 0, 0, 0, 0, 0, 0 },
  { 0, 0, 0, 0, 0, 0 },
  { 0, 0, 0, 0, 0, 0 },
  { 0, 0, 0, 0, 0, 0 },
  { 0, 0, 0, 0, 0, 0 },
  { 0, 0, 0, 0, 0, 0 },
  { 0, 0, 0, 0, 0, 0 },
  { 0, 0, 0, 0, 0, 0 },
  { 0, 0, 0, 0, 0, 0 },
  { 0, 0, 0, 0, 0, 0 },
  { 0, 0, 0, 0, 0, 0 },
  { 0, 0, 0, 0, 0, 0 },
  { 0, 0, 0, 0, 0, 0 },
  { 0, 0, 0, 0, 0, 0 },
  { 0, 0, 0, 0, 0, 0 },
  { 0, 0, 0, 0, 0, 0 },
  { 0, 0, 0, 0, 0, 0 },
  { 0, 0, 0, 0, 0, 0 },
  { 0, 0, 0, 0, 0, 0 },
  { 0, 0, 0, 0, 0, 0 },
  { 0, 0, 0, 0, 0, 0 },
  { 0, 0, 0, 0, 0, 0 },
  { 0, 0, 0, 0, 0, 0 },
  { 0, 0, 0, 0, 0, 0 },
  { 0, 0, 0, 0, 0, 0 },
  { 0, 0, 0, 0, 0, 0 },
  { 0, 0, 0, 0, 0, 0 },
  { 0, 0, 0, 0, 0, 0 },
  { 0, 0, 0, 0, 0, 0 },
  { 0, 0, 0, 0, 0, 0 }
};
==================================================================
Comment 1 Volker Reichelt 2009-05-05 22:00:19 UTC 
Here's a reduced version without includes:

===============================================
struct X
{
  X(int, const int& = 0);
  ~X();
};

X x[2][3] = { { 0, 0, 0 }, { 0, 0, 0 } };

struct A
{
  A(int);
};

struct B
{
  A a1, a2, a3, a4, a5, a6;
};

B b[42] =
{
  { 0, 0, 0, 0, 0, 0 },
  { 0, 0, 0, 0, 0, 0 },
  { 0, 0, 0, 0, 0, 0 },
  { 0, 0, 0, 0, 0, 0 },
  { 0, 0, 0, 0, 0, 0 },
  { 0, 0, 0, 0, 0, 0 },
  { 0, 0, 0, 0, 0, 0 },
  { 0, 0, 0, 0, 0, 0 },
  { 0, 0, 0, 0, 0, 0 },
  { 0, 0, 0, 0, 0, 0 },
  { 0, 0, 0, 0, 0, 0 },
  { 0, 0, 0, 0, 0, 0 },
  { 0, 0, 0, 0, 0, 0 },
  { 0, 0, 0, 0, 0, 0 },
  { 0, 0, 0, 0, 0, 0 },
  { 0, 0, 0, 0, 0, 0 },
  { 0, 0, 0, 0, 0, 0 },
  { 0, 0, 0, 0, 0, 0 },
  { 0, 0, 0, 0, 0, 0 },
  { 0, 0, 0, 0, 0, 0 },
  { 0, 0, 0, 0, 0, 0 },
  { 0, 0, 0, 0, 0, 0 },
  { 0, 0, 0, 0, 0, 0 },
  { 0, 0, 0, 0, 0, 0 },
  { 0, 0, 0, 0, 0, 0 },
  { 0, 0, 0, 0, 0, 0 },
  { 0, 0, 0, 0, 0, 0 },
  { 0, 0, 0, 0, 0, 0 },
  { 0, 0, 0, 0, 0, 0 },
  { 0, 0, 0, 0, 0, 0 },
  { 0, 0, 0, 0, 0, 0 },
  { 0, 0, 0, 0, 0, 0 },
  { 0, 0, 0, 0, 0, 0 },
  { 0, 0, 0, 0, 0, 0 },
  { 0, 0, 0, 0, 0, 0 },
  { 0, 0, 0, 0, 0, 0 },
  { 0, 0, 0, 0, 0, 0 },
  { 0, 0, 0, 0, 0, 0 },
  { 0, 0, 0, 0, 0, 0 },
  { 0, 0, 0, 0, 0, 0 },
  { 0, 0, 0, 0, 0, 0 },
  { 0, 0, 0, 0, 0, 0 }
};
===============================================
Comment 2 Andrew Pinski 2009-06-22 00:43:26 UTC 
Confirmed.
Comment 3 Andrew Pinski 2009-09-18 04:17:01 UTC 
This works on the trunk with:
gcc version 4.5.0 20090917 (experimental) [trunk revision 151808] (GCC) 


It did produce a warning with:
gcc version 4.5.0 20090706 (experimental) [trunk revision 149292] (GCC)
Comment 4 Andrew Pinski 2009-09-28 20:11:04 UTC 
Fixed so closing as such.