[gcc r12-7856] gimple-fold: fix location of loads for memory ops [PR104308]

[gcc r12-7856] gimple-fold: fix location of loads for memory ops [PR104308]

[David Malcolm]

https://gcc.gnu.org/g:875342766d42988fa2f8eb7d34ef562ba69e340a

commit r12-7856-g875342766d42988fa2f8eb7d34ef562ba69e340a
Author: David Malcolm <dmalcolm@redhat.com>
Date:   Mon Mar 28 09:43:07 2022 -0400

    gimple-fold: fix location of loads for memory ops [PR104308]
    
    PR analyzer/104308 reports that when -Wanalyzer-use-of-uninitialized-value
    complains about certain memmove operations where the source is
    uninitialized, the diagnostic uses UNKNOWN_LOCATION:
    
    In function 'main':
    cc1: warning: use of uninitialized value '*(short unsigned int *)&s + 1' [CWE-457] [-Wanalyzer-use-of-uninitialized-value]
      'main': event 1
        |
        |pr104308.c:5:8:
        |    5 |   char s[5]; /* { dg-message "region created on stack here" } */
        |      |        ^
        |      |        |
        |      |        (1) region created on stack here
        |
      'main': event 2
        |
        |cc1:
        | (2): use of uninitialized value '*(short unsigned int *)&s + 1' here
        |
    
    The issue is that gimple_fold_builtin_memory_op converts a memmove to:
    
      _3 = MEM <unsigned short> [(char * {ref-all})_1];
      MEM <unsigned short> [(char * {ref-all})&s] = _3;
    
    but only sets the location of the 2nd stmt, not the 1st.
    
    Fixed thusly, giving:
    
    pr104308.c: In function 'main':
    pr104308.c:6:3: warning: use of uninitialized value '*(short unsigned int *)&s + 1' [CWE-457] [-Wanalyzer-use-of-uninitialized-value]
        6 |   memmove(s, s + 1, 2); /* { dg-warning "use of uninitialized value" } */
          |   ^~~~~~~~~~~~~~~~~~~~
      'main': events 1-2
        |
        |    5 |   char s[5]; /* { dg-message "region created on stack here" } */
        |      |        ^
        |      |        |
        |      |        (1) region created on stack here
        |    6 |   memmove(s, s + 1, 2); /* { dg-warning "use of uninitialized value" } */
        |      |   ~~~~~~~~~~~~~~~~~~~~
        |      |   |
        |      |   (2) use of uninitialized value '*(short unsigned int *)&s + 1' here
        |
    
    One side-effect of this change is a change in part of the output of
    gcc.dg/uninit-40.c from:
    
      uninit-40.c:47:3: warning: ‘*(long unsigned int *)(&u[1][0][0])’ is used uninitialized [-Wuninitialized]
         47 |   __builtin_memcpy (&v[1], &u[1], sizeof (V));
            |   ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
      uninit-40.c:45:5: note: ‘*(long unsigned int *)(&u[1][0][0])’ was declared here
         45 |   V u[2], v[2];
            |     ^
    
    to:
    
      uninit-40.c:47:3: warning: ‘u’ is used uninitialized [-Wuninitialized]
         47 |   __builtin_memcpy (&v[1], &u[1], sizeof (V));
            |   ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
      uninit-40.c:45:5: note: ‘u’ declared here
         45 |   V u[2], v[2];
            |     ^
    
    What's happening is that pass "early_uninit"(29)'s call to
    maybe_warn_operand is guarded by this condition:
      1051            else if (gimple_assign_load_p (stmt)
      1052                     && gimple_has_location (stmt))
    
    Before the patch, the stmt:
      _3 = MEM <unsigned long> [(char * {ref-all})&u + 8B];
    has no location, and so early_uninit skips this operand at line
    1052 above.  Later, pass "uninit"(217) tests the var_decl "u$8", and
    emits a warning for it.
    
    With the patch, the stmt has a location, and so early_uninit emits a
    warning for "u" and sets a NW_UNINIT warning suppression at that
    location.  Later, pass "uninit"(217)'s test of "u$8" is rejected
    due to that per-location suppression of uninit warnings, from the
    earlier warning.
    
    gcc/ChangeLog:
            PR analyzer/104308
            * gimple-fold.cc (gimple_fold_builtin_memory_op): When optimizing
            to loads then stores, set the location of the new load stmt.
    
    gcc/testsuite/ChangeLog:
            PR analyzer/104308
            * gcc.dg/analyzer/pr104308.c: New test.
            * gcc.dg/uninit-40.c (foo): Update expression in expected message.
    
    Signed-off-by: David Malcolm <dmalcolm@redhat.com>

Diff:
---
 gcc/gimple-fold.cc                       | 1 +
 gcc/testsuite/gcc.dg/analyzer/pr104308.c | 8 ++++++++
 gcc/testsuite/gcc.dg/uninit-40.c         | 2 +-
 3 files changed, 10 insertions(+), 1 deletion(-)

diff --git a/gcc/gimple-fold.cc b/gcc/gimple-fold.cc
index 5eff7d68ac1..e73bc6a7137 100644
--- a/gcc/gimple-fold.cc
+++ b/gcc/gimple-fold.cc
@@ -1039,6 +1039,7 @@ gimple_fold_builtin_memory_op (gimple_stmt_iterator *gsi,
 							  new_stmt);
 			  gimple_assign_set_lhs (new_stmt, srcmem);
 			  gimple_set_vuse (new_stmt, gimple_vuse (stmt));
+			  gimple_set_location (new_stmt, loc);
 			  gsi_insert_before (gsi, new_stmt, GSI_SAME_STMT);
 			}
 		      if (dest_align < GET_MODE_ALIGNMENT (mode))
diff --git a/gcc/testsuite/gcc.dg/analyzer/pr104308.c b/gcc/testsuite/gcc.dg/analyzer/pr104308.c
new file mode 100644
index 00000000000..9cd5ee6feee
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/analyzer/pr104308.c
@@ -0,0 +1,8 @@
+#include <string.h>
+
+int main()
+{
+  char s[5]; /* { dg-message "region created on stack here" } */
+  memmove(s, s + 1, 2); /* { dg-warning "use of uninitialized value" } */
+  return 0;
+}
diff --git a/gcc/testsuite/gcc.dg/uninit-40.c b/gcc/testsuite/gcc.dg/uninit-40.c
index 8708079d397..567707a885e 100644
--- a/gcc/testsuite/gcc.dg/uninit-40.c
+++ b/gcc/testsuite/gcc.dg/uninit-40.c
@@ -44,7 +44,7 @@ foo (int *q)
   /* memcpy folding is too target dependent to test it everywhere.  */
   V u[2], v[2];
   u[0][0][0] = 1;
-  __builtin_memcpy (&v[1], &u[1], sizeof (V));		/* { dg-warning "'\\*\\(\(long \)?long unsigned int \\*\\)\\(&u\\\[1\\\]\\\[0\\\]\\\[0\\\]\\)' is used uninitialized" "" { target i?86-*-* x86_64-*-* } } */
+  __builtin_memcpy (&v[1], &u[1], sizeof (V));		/* { dg-warning "'u' is used uninitialized" "" { target i?86-*-* x86_64-*-* } } */
   baz (&v[1]);
 #endif
 }