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From: "guojiufu at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug tree-optimization/102087] [12 Regression] ICE on valid code at
 -O3 on x86_64-linux-gnu: in determine_exit_conditions, at
 tree-ssa-loop-manip.c:1049 since r12-3136-g3673dcf6d6baeb67
Date: Fri, 27 Aug 2021 13:27:38 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D102087

--- Comment #6 from Jiu Fu Guo <guojiufu at gcc dot gnu.org> ---
Drafting patch to calculate three items: control, bound and cmp.
----
diff --git a/gcc/tree-ssa-loop-niter.c b/gcc/tree-ssa-loop-niter.c
index 7af92d1c893..c6e4b24fd83 100644
--- a/gcc/tree-ssa-loop-niter.c
+++ b/gcc/tree-ssa-loop-niter.c
@@ -1482,7 +1482,7 @@ number_of_iterations_until_wrap (class loop *, tree t=
ype,
affine_iv *iv0,
                                 affine_iv *iv1, class tree_niter_desc *nit=
er)
 {
   tree niter_type =3D unsigned_type_for (type);
-  tree step, num, assumptions, may_be_zero;
+  tree step, num, assumptions, may_be_zero, span;
   wide_int high, low, max, min;

   may_be_zero =3D fold_build2 (LE_EXPR, boolean_type_node, iv1->base,
iv0->base);
@@ -1513,6 +1513,8 @@ number_of_iterations_until_wrap (class loop *, tree t=
ype,
affine_iv *iv0,
        low =3D wi::to_wide (iv0->base);
       else
        low =3D min;
+
+      niter->control =3D *iv1;
     }
   /* {base, -C} < n.  */
   else if (tree_int_cst_sign_bit (iv0->step) && integer_zerop (iv1->step))
@@ -1533,6 +1535,8 @@ number_of_iterations_until_wrap (class loop *, tree t=
ype,
affine_iv *iv0,
        high =3D wi::to_wide (iv1->base);
       else
        high =3D max;
+
+      niter->control =3D *iv0;
     }
   else
     return false;
@@ -1556,6 +1560,14 @@ number_of_iterations_until_wrap (class loop *, tree
type, affine_iv *iv0,
                                      niter->assumptions, assumptions);

   niter->control.no_overflow =3D false;
+  tree niter_m1 =3D fold_build2 (MINUS_EXPR, niter_type, niter->niter,
+                             build_int_cst (niter_type, 1));
+  span =3D fold_build2 (MULT_EXPR, niter_type, niter_m1,
+                     fold_convert (niter_type, niter->control.step));
+  niter->bound =3D fold_build2 (PLUS_EXPR, niter_type, span,
+                             fold_convert (niter_type, niter->control.base=
));
+  niter->bound =3D fold_convert (type, niter->bound);
+  niter->cmp =3D NE_EXPR;

   return true;
 }
------------------------

While this code may generate complicated niter->bound if the step is not +-=
1.=