[gcc r12-4369] tree-optimization/102659 - avoid undefined overflow after if-conversion

[gcc r12-4369] tree-optimization/102659 - avoid undefined overflow after if-conversion

[Richard Biener]

https://gcc.gnu.org/g:3c0194d7ff21d61c02f3c6b111c83ef24a69e1f0

commit r12-4369-g3c0194d7ff21d61c02f3c6b111c83ef24a69e1f0
Author: Richard Biener <rguenther@suse.de>
Date:   Mon Oct 11 12:27:10 2021 +0200

    tree-optimization/102659 - avoid undefined overflow after if-conversion
    
    The following makes sure to rewrite arithmetic with undefined behavior
    on overflow to a well-defined variant when moving them to be always
    executed as part of doing if-conversion for loop vectorization.
    
    2021-10-11  Richard Biener  <rguenther@suse.de>
    
            PR tree-optimization/102659
            * tree-if-conv.c (need_to_rewrite_undefined): New flag.
            (if_convertible_gimple_assign_stmt_p): Mark the loop for
            rewrite when stmts with undefined behavior on integer
            overflow appear.
            (combine_blocks): Predicate also when we need to rewrite stmts.
            (predicate_statements): Rewrite affected stmts to something
            with well-defined behavior on overflow.
            (tree_if_conversion): Initialize need_to_rewrite_undefined.
    
            * gcc.dg/torture/pr69760.c: Adjust the testcase.
            * gcc.target/i386/avx2-vect-mask-store-move1.c: Expect to move
            the conversions to unsigned as well.

Diff:
---
 gcc/testsuite/gcc.dg/torture/pr69760.c             |  3 +--
 .../gcc.target/i386/avx2-vect-mask-store-move1.c   |  2 +-
 gcc/tree-if-conv.c                                 | 28 +++++++++++++++++++++-
 3 files changed, 29 insertions(+), 4 deletions(-)

diff --git a/gcc/testsuite/gcc.dg/torture/pr69760.c b/gcc/testsuite/gcc.dg/torture/pr69760.c
index 53733c7c6a4..47e01ae59bd 100644
--- a/gcc/testsuite/gcc.dg/torture/pr69760.c
+++ b/gcc/testsuite/gcc.dg/torture/pr69760.c
@@ -1,11 +1,10 @@
 /* PR tree-optimization/69760 */
 /* { dg-do run { target { { *-*-linux* *-*-gnu* *-*-uclinux* } && mmap } } } */
-/* { dg-options "-O2" } */
 
 #include <unistd.h>
 #include <sys/mman.h>
 
-__attribute__((noinline, noclone)) void
+__attribute__((noinline, noclone)) static void
 test_func (double *a, int L, int m, int n, int N)
 {
   int i, k;
diff --git a/gcc/testsuite/gcc.target/i386/avx2-vect-mask-store-move1.c b/gcc/testsuite/gcc.target/i386/avx2-vect-mask-store-move1.c
index 989ba402e0e..6a47a09c835 100644
--- a/gcc/testsuite/gcc.target/i386/avx2-vect-mask-store-move1.c
+++ b/gcc/testsuite/gcc.target/i386/avx2-vect-mask-store-move1.c
@@ -78,4 +78,4 @@ avx2_test (void)
       abort ();
 }
 
-/* { dg-final { scan-tree-dump-times "Move stmt to created bb" 6 "vect" } } */
+/* { dg-final { scan-tree-dump-times "Move stmt to created bb" 10 "vect" } } */
diff --git a/gcc/tree-if-conv.c b/gcc/tree-if-conv.c
index d7b7b309309..6a67acfeaae 100644
--- a/gcc/tree-if-conv.c
+++ b/gcc/tree-if-conv.c
@@ -132,6 +132,11 @@ along with GCC; see the file COPYING3.  If not see
    predicate_statements for the kinds of predication we support.  */
 static bool need_to_predicate;
 
+/* True if we have to rewrite stmts that may invoke undefined behavior
+   when a condition C was false so it doesn't if it is always executed.
+   See predicate_statements for the kinds of predication we support.  */
+static bool need_to_rewrite_undefined;
+
 /* Indicate if there are any complicated PHIs that need to be handled in
    if-conversion.  Complicated PHI has more than two arguments and can't
    be degenerated to two arguments PHI.  See more information in comment
@@ -1042,6 +1047,12 @@ if_convertible_gimple_assign_stmt_p (gimple *stmt,
 	fprintf (dump_file, "tree could trap...\n");
       return false;
     }
+  else if (INTEGRAL_TYPE_P (TREE_TYPE (lhs))
+	   && TYPE_OVERFLOW_UNDEFINED (TREE_TYPE (lhs))
+	   && arith_code_with_undefined_signed_overflow
+				(gimple_assign_rhs_code (stmt)))
+    /* We have to rewrite stmts with undefined overflow.  */
+    need_to_rewrite_undefined = true;
 
   /* When if-converting stores force versioning, likewise if we
      ended up generating store data races.  */
@@ -2563,6 +2574,20 @@ predicate_statements (loop_p loop)
 
 	      gsi_replace (&gsi, new_stmt, true);
 	    }
+	  else if (INTEGRAL_TYPE_P (TREE_TYPE (gimple_assign_lhs (stmt)))
+		   && TYPE_OVERFLOW_UNDEFINED
+			(TREE_TYPE (gimple_assign_lhs (stmt)))
+		   && arith_code_with_undefined_signed_overflow
+						(gimple_assign_rhs_code (stmt)))
+	    {
+	      gsi_remove (&gsi, true);
+	      gsi_insert_seq_before (&gsi, rewrite_to_defined_overflow (stmt),
+				     GSI_SAME_STMT);
+	      if (gsi_end_p (gsi))
+		gsi = gsi_last_bb (gimple_bb (stmt));
+	      else
+		gsi_prev (&gsi);
+	    }
 	  else if (gimple_vdef (stmt))
 	    {
 	      tree lhs = gimple_assign_lhs (stmt);
@@ -2647,7 +2672,7 @@ combine_blocks (class loop *loop)
   insert_gimplified_predicates (loop);
   predicate_all_scalar_phis (loop);
 
-  if (need_to_predicate)
+  if (need_to_predicate || need_to_rewrite_undefined)
     predicate_statements (loop);
 
   /* Merge basic blocks.  */
@@ -3148,6 +3173,7 @@ tree_if_conversion (class loop *loop, vec<gimple *> *preds)
   rloop = NULL;
   ifc_bbs = NULL;
   need_to_predicate = false;
+  need_to_rewrite_undefined = false;
   any_complicated_phi = false;
 
   /* Apply more aggressive if-conversion when loop or its outer loop were