[gcc r14-4789] tree-optimization/110243 - IVOPTs introducing undefined overflow

[gcc r14-4789] tree-optimization/110243 - IVOPTs introducing undefined overflow

[Richard Biener]

https://gcc.gnu.org/g:44e7e4498c3cdc27e087ab80aa76dac41819702f

commit r14-4789-g44e7e4498c3cdc27e087ab80aa76dac41819702f
Author: Richard Biener <rguenther@suse.de>
Date:   Fri Oct 20 14:08:46 2023 +0200

    tree-optimization/110243 - IVOPTs introducing undefined overflow
    
    The following addresses IVOPTs rewriting expressions in its
    strip_offset without caring for definedness of overflow.  Rather
    than the earlier attempt of just using the proper
    split_constant_offset from data-ref analysis the following adjusts
    IVOPTs helper trying to minimize changes from this fix, possibly
    easing backports.
    
            PR tree-optimization/110243
            PR tree-optimization/111336
            * tree-ssa-loop-ivopts.cc (strip_offset_1): Rewrite
            operations with undefined behavior on overflow to
            unsigned arithmetic.
    
            * gcc.dg/torture/pr110243.c: New testcase.
            * gcc.dg/torture/pr111336.c: Likewise.

Diff:
---
 gcc/testsuite/gcc.dg/torture/pr110243.c | 22 ++++++++++++++++++++++
 gcc/testsuite/gcc.dg/torture/pr111336.c | 25 +++++++++++++++++++++++++
 gcc/tree-ssa-loop-ivopts.cc             | 31 ++++++++++++++++++++++++++++---
 3 files changed, 75 insertions(+), 3 deletions(-)

diff --git a/gcc/testsuite/gcc.dg/torture/pr110243.c b/gcc/testsuite/gcc.dg/torture/pr110243.c
new file mode 100644
index 000000000000..07dffd95d4d4
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/torture/pr110243.c
@@ -0,0 +1,22 @@
+/* { dg-do run } */
+/* { dg-require-effective-target lp64 } */
+
+#define X 1100000000
+unsigned char a;
+long b = X;
+int c[9][1];
+unsigned d;
+static long *e = &b, *f = &b;
+int g() {
+  if (a && a <= '9')
+    return '0';
+  if (a)
+    return 10;
+  return -1;
+}
+int main() {
+  d = 0;
+  for (; (int)*f -(X-1) + d < 9; d++)
+    c[g() + (int)*f + ((int)*e - X) -(X-1) + d]
+     [0] = 0;
+}
diff --git a/gcc/testsuite/gcc.dg/torture/pr111336.c b/gcc/testsuite/gcc.dg/torture/pr111336.c
new file mode 100644
index 000000000000..a2fa12258dfb
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/torture/pr111336.c
@@ -0,0 +1,25 @@
+/* { dg-do run } */
+/* { dg-require-effective-target lp64 } */
+
+extern void abort (void);
+int a, b;
+long c = 3521733542;
+int d[2];
+int e(int f, int g) {
+  if (f == 0)
+    return 0;
+  if (f > 200)
+    return 0;
+  if (g)
+    return 5 * f;
+  return 0;
+}
+int main()
+{
+  int h = 0;
+  for (; e((int)c + 773233762, c + 60) + 773163185 + h < 2; h++)
+    d[h] = b;
+  if (a != 0)
+    abort ();
+  return 0;
+}
diff --git a/gcc/tree-ssa-loop-ivopts.cc b/gcc/tree-ssa-loop-ivopts.cc
index 2c1f0846c88d..98e5b3024db3 100644
--- a/gcc/tree-ssa-loop-ivopts.cc
+++ b/gcc/tree-ssa-loop-ivopts.cc
@@ -2829,12 +2829,29 @@ strip_offset_1 (tree expr, bool inside_addr, bool top_compref,
       else if (integer_zerop (op0))
 	{
 	  if (code == MINUS_EXPR)
-	    expr = fold_build1 (NEGATE_EXPR, type, op1);
+	    {
+	      if (TYPE_OVERFLOW_UNDEFINED (type))
+		{
+		  type = unsigned_type_for (type);
+		  op1 = fold_convert (type, op1);
+		}
+	      expr = fold_build1 (NEGATE_EXPR, type, op1);
+	    }
 	  else
 	    expr = op1;
 	}
       else
-	expr = fold_build2 (code, type, op0, op1);
+	{
+	  if (TYPE_OVERFLOW_UNDEFINED (type))
+	    {
+	      type = unsigned_type_for (type);
+	      if (code == POINTER_PLUS_EXPR)
+		code = PLUS_EXPR;
+	      op0 = fold_convert (type, op0);
+	      op1 = fold_convert (type, op1);
+	    }
+	  expr = fold_build2 (code, type, op0, op1);
+	}
 
       return fold_convert (orig_type, expr);
 
@@ -2852,7 +2869,15 @@ strip_offset_1 (tree expr, bool inside_addr, bool top_compref,
       if (integer_zerop (op0))
 	expr = op0;
       else
-	expr = fold_build2 (MULT_EXPR, type, op0, op1);
+	{
+	  if (TYPE_OVERFLOW_UNDEFINED (type))
+	    {
+	      type = unsigned_type_for (type);
+	      op0 = fold_convert (type, op0);
+	      op1 = fold_convert (type, op1);
+	    }
+	  expr = fold_build2 (MULT_EXPR, type, op0, op1);
+	}
 
       return fold_convert (orig_type, expr);