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[COMMITTED] Handle constants in wi_fold for trunc_mod.

Message ID bdf04dc7-4718-e658-d3e0-0a7ee03a9f49@redhat.com
State New
Headers show
Series [COMMITTED] Handle constants in wi_fold for trunc_mod. | expand

Commit Message

Andrew MacLeod July 30, 2021, 7:12 p.m. UTC 
When resolving issues with divide by 0 returning UNDEFINED, I discovered 
that although we treat % 0 as undefined, the implementation of wi_fold 
for modulus doesn't expect constants, and with the earlier changes to 
wi_fold_in_parts, it can now get constants to calculate and combine. ie

[10,10] % [4,4] was returning [0,3] instead of calculating the more 
precise  [2,2].  This patch fixes that, and I updated the testcase to 
incluide a more comprehensive test of modulus with constants.

Bootstrapped on x86_64-pc-linux-gnu and powerpc64-unknown-linux-gnu with 
no regressions.  Pushed.

Andrew
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Patch

From 145bc41dae7c7bfa093d61e77346f98e6a595a0e Mon Sep 17 00:00:00 2001
From: Andrew MacLeod <amacleod@redhat.com>
Date: Thu, 29 Jul 2021 11:22:28 -0400
Subject: [PATCH 3/3] Handle constants in wi_fold for trunc_mod.

Handle const % const, as wi_fold_in_parts may now provide this.  Before this
[10, 10] % [4, 4] would produce [0, 3] instead of [2, 2].

	gcc/
	* range-op.cc (operator_trunc_mod::wi_fold): Fold constants.

	gcc/testsuite/
	* gcc.dg/tree-ssa/pr61839_2.c: Adjust.  Add new const fold test.
---
 gcc/range-op.cc                           | 12 +++++++
 gcc/testsuite/gcc.dg/tree-ssa/pr61839_2.c | 39 ++++++++++++++++++++---
 2 files changed, 47 insertions(+), 4 deletions(-)

diff --git a/gcc/range-op.cc b/gcc/range-op.cc
index 69228882930..eb66e12677f 100644
--- a/gcc/range-op.cc
+++ b/gcc/range-op.cc
@@ -3240,6 +3240,18 @@  operator_trunc_mod::wi_fold (irange &r, tree type,
       return;
     }
 
+  // Check for constant and try to fold.
+  if (lh_lb == lh_ub && rh_lb == rh_ub)
+    {
+      wi::overflow_type ov = wi::OVF_NONE;
+      tmp = wi::mod_trunc (lh_lb, rh_lb, sign, &ov);
+      if (ov == wi::OVF_NONE)
+	{
+	  r = int_range<2> (type, tmp, tmp);
+	  return;
+	}
+    }
+
   // ABS (A % B) < ABS (B) and either 0 <= A % B <= A or A <= A % B <= 0.
   new_ub = rh_ub - 1;
   if (sign == SIGNED)
diff --git a/gcc/testsuite/gcc.dg/tree-ssa/pr61839_2.c b/gcc/testsuite/gcc.dg/tree-ssa/pr61839_2.c
index f1b8feb4e9d..0e0f4c02113 100644
--- a/gcc/testsuite/gcc.dg/tree-ssa/pr61839_2.c
+++ b/gcc/testsuite/gcc.dg/tree-ssa/pr61839_2.c
@@ -45,9 +45,40 @@  int bar2 ()
   return 0;
 }
 
-/* Dont optimize 972195717 / 0 in function foo.  */
+/* Ensure we are folding modulus sub-ranges properly.  */
+__attribute__ ((noinline))
+int mod (int a, int b)
+{
+  int v1, v2;
+  v1 = (a < 10) ? 12 : 24;
+  v2 = (b > 20) ? 3 : 6;
+
+  if (a > 20)
+    v1 = v1 * 2;
+  if (b > 20)
+    v2 = v2 * 2;
+
+  if (a == b)
+    v2 = 0;
+    
+  /* v1 == 12, 24, or 48.  v2 == 0, 3, 6, or 12. */
+  int c = v1 % v2;
+  if (c == 0)
+    ;
+  else
+    __builtin_abort ();
+  return 0;
+}
+
+/* EVRP now makes transformations in all functions, leaving a single
+ * builtin_abort call in bar2. */
+/* { dg-final { scan-tree-dump-times "__builtin_abort" 1 "evrp" } } */
+
+/* Make sure to optimize 972195717 / 0 in function foo.  */
 /* { dg-final { scan-tree-dump-times "972195717 / " 0  "evrp" } } */
-/* Dont optimize 972195717 % 0 in function bar.  */
-/* { dg-final { scan-tree-dump-times "972195717 % " 1 "evrp" } } */
-/* May optimize in function bar2, but EVRP doesn't perform this yet.  */
+/* Make sure  to optimize 972195717 % 0 in function bar.  */
+/* { dg-final { scan-tree-dump-times "972195717 % " 0 "evrp" } } */
+/* Make sure to optimize 972195717 % [1,2] function bar2.  */
 /* { dg-final { scan-tree-dump-times "972195715 % " 0 "evrp" } } */
+/* [12,12][24,24][48,48] % [0,0][3,3][6,6][12,12] == [0,0] */
+/* { dg-final { scan-tree-dump-times "%" 0 "evrp" } } */
-- 
2.17.2