operator_lshift::op1_range was not handling UNDEFINED properly if it
determined that there was no combination of LHS and OP2 that resulted in
a value.
Return false which indicates we should stop trying to calculate a range,
which will also terminate the reverse search for a value. If the edge or
block is undefined, trying to produce a value has little value.
Bootstrapped on x86_64-pc-linux-gnu with no regressions. Pushed.
Andrew
From 0bf6e399dbc8e1f6d2b3f7e0f3a0cab9ac55b572 Mon Sep 17 00:00:00 2001
From: Andrew MacLeod <[email protected]>
Date: Wed, 5 Aug 2026 14:05:33 -0400
Subject: [PATCH 1/4] Check for undefined in operator_lshift::op1_range.
If we conclude that the op1_range calculation is undefined, simply
abort the calculation.
PR tree-optimization/126648
gcc/
* range-op.cc (operator_lshift::op1_range): Handle undefined.
gcc/testsuite/
* gcc.dg/pr126648.c: New.
---
gcc/range-op.cc | 4 ++++
gcc/testsuite/gcc.dg/pr126648.c | 31 +++++++++++++++++++++++++++++++
2 files changed, 35 insertions(+)
create mode 100644 gcc/testsuite/gcc.dg/pr126648.c
diff --git a/gcc/range-op.cc b/gcc/range-op.cc
index 07413ef7054..333ac748815 100644
--- a/gcc/range-op.cc
+++ b/gcc/range-op.cc
@@ -2897,6 +2897,10 @@ operator_lshift::op1_range (irange &r,
else
op_rshift.fold_range (tmp_range, utype, lhs, op2);
+ // If no valid range is found, abort the calculation and return falae.
+ if (tmp_range.undefined_p ())
+ return false;
+
// Start with ranges which can produce the LHS by right shifting the
// result by the shift amount.
// ie [0x08, 0xF0] = op1 << 2 will start with
diff --git a/gcc/testsuite/gcc.dg/pr126648.c b/gcc/testsuite/gcc.dg/pr126648.c
new file mode 100644
index 00000000000..44272d20e44
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/pr126648.c
@@ -0,0 +1,31 @@
+/* { dg-do compile } */
+/* { dg-options "-O3" } */
+long a;
+char b;
+short c;
+int f(int g) {
+ {
+ unsigned h = g;
+ {
+ long d = h;
+ int e = 0;
+ do {
+ if ((h & 15) == 4)
+ d = d + (h << 5);
+ if (d == 5)
+ break;
+ e = e + 1;
+ } while (e < 3);
+ c = d;
+ }
+ }
+ return c;
+}
+char k() {
+ long i;
+ unsigned j = b % 6u + 4;
+ while (a)
+ i = f(j + 826);
+ return i;
+}
+int main() {}
--
2.45.0
