[gcc r12-7239] tree-optimization/104519 - adjust PR100499 niter fix

[Richard Biener]

https://gcc.gnu.org/g:d8b6da8dd15240849e00d46f3aef40cb8eeb1dc5

commit r12-7239-gd8b6da8dd15240849e00d46f3aef40cb8eeb1dc5
Author: Richard Biener <rguenther@suse.de>
Date:   Tue Feb 15 09:40:59 2022 +0100

    tree-optimization/104519 - adjust PR100499 niter fix
    
    The following adjusts the PR100499 niter fix to use the appropriate
    types when checking whether the difference between the final and base
    values of the IV are a multiple of the step.  It also gets rid of
    an always false condition in multiple_of_p which lead me to a
    wrong solution first.
    
    2022-02-15  Richard Biener  <rguenther@suse.de>
    
            PR tree-optimization/104519
            * fold-const.cc (multiple_of_p): Remove never true condition.
            * tree-ssa-loop-niter.cc (number_of_iterations_ne): Use
            the appropriate types for determining whether the difference
            of final and base is a multiple of the step.
    
            * gcc.dg/torture/pr104519.c: New testcase.

Diff:
---
 gcc/fold-const.cc                       |  6 +-----
 gcc/testsuite/gcc.dg/torture/pr104519.c | 10 ++++++++++
 gcc/tree-ssa-loop-niter.cc              | 16 +++++++++++-----
 3 files changed, 22 insertions(+), 10 deletions(-)

diff --git a/gcc/fold-const.cc b/gcc/fold-const.cc
index 386d5732ea0..9d9939642f6 100644
--- a/gcc/fold-const.cc
+++ b/gcc/fold-const.cc
@@ -14208,11 +14208,7 @@ multiple_of_p (tree type, const_tree top, const_tree bottom, bool nowrap)
 	      && multiple_of_p (type, TREE_OPERAND (top, 2), bottom, nowrap));
 
     case INTEGER_CST:
-      if (TREE_CODE (bottom) != INTEGER_CST
-	  || integer_zerop (bottom)
-	  || (TYPE_UNSIGNED (type)
-	      && (tree_int_cst_sgn (top) < 0
-		  || tree_int_cst_sgn (bottom) < 0)))
+      if (TREE_CODE (bottom) != INTEGER_CST || integer_zerop (bottom))
 	return 0;
       return wi::multiple_of_p (wi::to_widest (top), wi::to_widest (bottom),
 				SIGNED);
diff --git a/gcc/testsuite/gcc.dg/torture/pr104519.c b/gcc/testsuite/gcc.dg/torture/pr104519.c
new file mode 100644
index 00000000000..389c7bb6880
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/torture/pr104519.c
@@ -0,0 +1,10 @@
+/* { dg-do run } */
+
+signed char a, b;
+int main()
+{
+  for (b = -7; b; b += 3)
+    if (a)
+      __builtin_abort();
+  return 0;
+}
diff --git a/gcc/tree-ssa-loop-niter.cc b/gcc/tree-ssa-loop-niter.cc
index 318d10c8fac..9bb5097379b 100644
--- a/gcc/tree-ssa-loop-niter.cc
+++ b/gcc/tree-ssa-loop-niter.cc
@@ -1048,13 +1048,19 @@ number_of_iterations_ne (class loop *loop, tree type, affine_iv *iv,
      which the loop exits immediately, and the iv does not overflow.
 
      Also note, we prove condition 2) by checking base and final seperately
-     along with condition 1) or 1').  */
+     along with condition 1) or 1').  Since we ensure the difference
+     computation of c does not wrap with cond below and the adjusted s
+     will fit a signed type as well as an unsigned we can safely do
+     this using the type of the IV if it is not pointer typed.  */
+  tree mtype = type;
+  if (POINTER_TYPE_P (type))
+    mtype = niter_type;
   if (!niter->control.no_overflow
       && (integer_onep (s)
-	  || (multiple_of_p (type, fold_convert (niter_type, iv->base), s,
-			     false)
-	      && multiple_of_p (type, fold_convert (niter_type, final), s,
-				false))))
+	  || (multiple_of_p (mtype, fold_convert (mtype, iv->base),
+			     fold_convert (mtype, s), false)
+	      && multiple_of_p (mtype, fold_convert (mtype, final),
+				fold_convert (mtype, s), false))))
     {
       tree t, cond, relaxed_cond = boolean_false_node;