When adjusting the value range of an induction variable using SCEV, VRP
calls scev_probably_wraps_p() with use_overflow_semantics=true. This
parameter set to true makes scev_probably_wraps_p() assume that signed
induction variables never wrap, so for these variables it always returns
false (when strict overflow rules are in effect). This is wrong because
if a signed induction variable really does overflow then we want to give
it an INF(OVF) value range and not the (finite) estimation returned by
SCEV.
While this change shouldn't make a difference in code generation, it
should help improve the coverage of -Wstrict-overflow warnings on
induction variables like in the test case.
OK after bootstrap + regtest on x86_64-unknown-linux-gnu?
gcc/
* tree-vrp.c (adjust_range_with_scev): Call
scev_probably_wraps_p with use_overflow_semantics=false.
gcc/testsuite/
* gcc.dg/Wstrict-overflow-27.c: New test.
---
gcc/testsuite/gcc.dg/Wstrict-overflow-27.c | 22 ++++++++++++++++++++++
gcc/tree-vrp.c | 2 +-
2 files changed, 23 insertions(+), 1 deletion(-)
create mode 100644 gcc/testsuite/gcc.dg/Wstrict-overflow-27.c
diff --git a/gcc/testsuite/gcc.dg/Wstrict-overflow-27.c
b/gcc/testsuite/gcc.dg/Wstrict-overflow-27.c
new file mode 100644
index 0000000..c1f27ab
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/Wstrict-overflow-27.c
@@ -0,0 +1,22 @@
+/* { dg-do compile } */
+/* { dg-options "-fstrict-overflow -O2 -Wstrict-overflow" } */
+
+/* Warn about an overflow when folding i < 0. */
+
+void bar (unsigned *p);
+
+int
+foo (unsigned *p)
+{
+ int i;
+ int sum = 0;
+
+ for (i = 0; i < *p; i++)
+ {
+ if (i < 0) /* { dg-warning "signed overflow" } */
+ sum += 2;
+ bar (p);
+ }
+
+ return sum;
+}
diff --git a/gcc/tree-vrp.c b/gcc/tree-vrp.c
index a75138f..bf9ff61 100644
--- a/gcc/tree-vrp.c
+++ b/gcc/tree-vrp.c
@@ -4270,7 +4270,7 @@ adjust_range_with_scev (value_range_t *vr, struct loop
*loop,
dir == EV_DIR_UNKNOWN
/* ... or if it may wrap. */
|| scev_probably_wraps_p (init, step, stmt, get_chrec_loop (chrec),
- true))
+ /*use_overflow_semantics=*/false))
return;
/* We use TYPE_MIN_VALUE and TYPE_MAX_VALUE here instead of
--
2.2.0.rc1.23.gf570943
