[Bug tree-optimization/92683] [10 Regression] strncmp incorrect result with equal substrings and non-const bound

[msebor at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=92683

--- Comment #5 from Martin Sebor <msebor at gcc dot gnu.org> ---
With pr92733 resolved I can verify that the test case from comment #0 is
compiled correctly by the sparc-sun-solaris2.11 cross:

$ cat pr92683.c && /build/sparc-sun-solaris2.11/gcc-svn/gcc/xgcc -B
/build/sparc-sun-solaris2.11/gcc-svn/gcc -O1 -S -Wall -Wextra
-fdump-tree-forwprop1=/dev/stdout pr92683.c


int f (void)
{
  return __builtin_strncmp ("123", "1234", 3);   // correctly folded to zero
}

int g (void)
{
  int n = 3;
  return __builtin_strncmp ("123", "1234", n);   // incorrectly folded to -1
}

;; Function f (f, funcdef_no=0, decl_uid=1482, cgraph_uid=1, symbol_order=0)

f ()
{
  <bb 2> :
  return 0;

}



;; Function g (g, funcdef_no=1, decl_uid=1485, cgraph_uid=2, symbol_order=1)

g ()
{
  int n;

  <bb 2> :
  return 0;

}



The gcc.dg/strcmpopt_8.c test also passes for me when compiled with the
sparc-sun-solaris2.11 cross:

$ nice make -C /build/sparc-sun-solaris2.11/gcc-svn/gcc check-c  'CFLAGS=-O0
-g3' 'CXXFLAGS=-O0 -g3' 'STAGE1_CFLAGS=-O0 -g3' 'STAGE1_CXXFLAGS=-O0 -g3'
RUNTESTFLAGS="dg.exp=gcc.dg/strcmpopt_8.c"
make: Entering directory '/ssd/build/sparc-sun-solaris2.11/gcc-svn/gcc'
...
Test run by msebor on Fri Nov 29 11:59:25 2019
Target is sparc-sun-solaris2.11
Host   is x86_64-pc-linux-gnu

                === gcc tests ===

Schedule of variations:
    unix

Running target unix
Using /usr/share/dejagnu/baseboards/unix.exp as board description file for
target.
Using /usr/share/dejagnu/config/unix.exp as generic interface file for target.
Using /src/gcc/svn/gcc/testsuite/config/default.exp as tool-and-target-specific
interface file.
WARNING: Assuming target board is the local machine (which is probably wrong).
You may need to set your DEJAGNU environment variable.
Running /src/gcc/svn/gcc/testsuite/gcc.dg/dg.exp ...

                === gcc Summary ===

# of expected passes            4
/ssd/build/sparc-sun-solaris2.11/gcc-svn/gcc/xgcc  version 10.0.0 20191129
(experimental) (GCC) 

make[1]: Leaving directory '/ssd/build/sparc-sun-solaris2.11/gcc-svn/gcc'
make: Leaving directory '/ssd/build/sparc-sun-solaris2.11/gcc-svn/gcc'


The output looks as expected:

$ /build/sparc-sun-solaris2.11/gcc-svn/gcc/xgcc -B
/build/sparc-sun-solaris2.11/gcc-svn/gcc -O1 -S -Wall -Wextra
-fdump-tree-forwprop1=/dev/stdout
/src/gcc/svn/gcc/testsuite/gcc.dg/strcmpopt_8.c

;; Function test_literal (test_literal, funcdef_no=0, decl_uid=1485,
cgraph_uid=1, symbol_order=0)

test_literal ()
{
  int zero;
  size_t max;

  <bb 2> :
  return;

}



;; Function test_cst_array (test_cst_array, funcdef_no=1, decl_uid=1492,
cgraph_uid=2, symbol_order=3)

test_cst_array ()
{
  int zero;
  size_t max;

  <bb 2> :
  return;

}