Hi!
POINTER_DIFF_EXPR returns a signed integer, but sadly POINTER_PLUS_EXPR
second arguments are unsigned integers, so if we are adding negative numbers
to pointers, those are very large numbers and we get TREE_OVERFLOW which the
C FE then during c_fully_fold diagnoses.
We want to treat the numbers as signed integers for this purpose, using
VCE seems easiest way to get rid of the unwanted overflows.
Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?
Or do you prefer manual fold_converts in the (with { }) block + test
for INTEGER_CST && TREE_OVERFLOW + drop_tree_overflow instead?
2018-01-17 Jakub Jelinek <ja...@redhat.com>
PR c/61240
* match.pd ((P + A) - P, P - (P + A), (P + A) - (P + B)): For
pointer_diff optimizations use view_convert instead of convert.
* gcc.dg/pr61240.c: New test.
--- gcc/match.pd.jj 2018-01-15 10:02:04.000000000 +0100
+++ gcc/match.pd 2018-01-17 17:10:54.855061485 +0100
@@ -1832,7 +1832,10 @@ DEFINE_INT_AND_FLOAT_ROUND_FN (RINT)
/* The second argument of pointer_plus must be interpreted as signed, and
thus sign-extended if necessary. */
(with { tree stype = signed_type_for (TREE_TYPE (@1)); }
- (convert (convert:stype @1))))
+ /* Use view_convert instead of convert here, as POINTER_PLUS_EXPR
+ second arg is unsigned even when we need to consider it as signed,
+ we don't want to diagnose overflow here. */
+ (convert (view_convert:stype @1))))
/* (T)P - (T)(P + A) -> -(T) A */
(simplify
@@ -1876,7 +1879,10 @@ DEFINE_INT_AND_FLOAT_ROUND_FN (RINT)
/* The second argument of pointer_plus must be interpreted as signed, and
thus sign-extended if necessary. */
(with { tree stype = signed_type_for (TREE_TYPE (@1)); }
- (negate (convert (convert:stype @1)))))
+ /* Use view_convert instead of convert here, as POINTER_PLUS_EXPR
+ second arg is unsigned even when we need to consider it as signed,
+ we don't want to diagnose overflow here. */
+ (negate (convert (view_convert:stype @1)))))
/* (T)(P + A) - (T)(P + B) -> (T)A - (T)B */
(simplify
@@ -1927,7 +1933,11 @@ DEFINE_INT_AND_FLOAT_ROUND_FN (RINT)
/* The second argument of pointer_plus must be interpreted as signed, and
thus sign-extended if necessary. */
(with { tree stype = signed_type_for (TREE_TYPE (@1)); }
- (minus (convert (convert:stype @1)) (convert (convert:stype @2)))))))
+ /* Use view_convert instead of convert here, as POINTER_PLUS_EXPR
+ second arg is unsigned even when we need to consider it as signed,
+ we don't want to diagnose overflow here. */
+ (minus (convert (view_convert:stype @1))
+ (convert (view_convert:stype @2)))))))
/* Simplifications of MIN_EXPR, MAX_EXPR, fmin() and fmax(). */
--- gcc/testsuite/gcc.dg/pr61240.c.jj 2018-01-17 17:25:45.821030898 +0100
+++ gcc/testsuite/gcc.dg/pr61240.c 2018-01-17 17:26:24.118029550 +0100
@@ -0,0 +1,20 @@
+/* PR c/61240 */
+/* { dg-do compile } */
+
+typedef __PTRDIFF_TYPE__ ptrdiff_t;
+
+ptrdiff_t
+foo (ptrdiff_t a[4])
+{
+ int i[4];
+ int *p = i + 2;
+ static ptrdiff_t b = p - (p - 1); /* { dg-bogus "integer overflow in
expression" } */
+ static ptrdiff_t c = (p - 1) - p; /* { dg-bogus "integer overflow in
expression" } */
+ static ptrdiff_t d = (p - 2) - (p - 1);/* { dg-bogus "integer overflow in
expression" } */
+ static ptrdiff_t e = (p - 1) - (p - 2);/* { dg-bogus "integer overflow in
expression" } */
+ a[0] = p - (p - 1); /* { dg-bogus "integer overflow in
expression" } */
+ a[1] = (p - 1) - p; /* { dg-bogus "integer overflow in
expression" } */
+ a[2] = (p - 2) - (p - 1); /* { dg-bogus "integer overflow in
expression" } */
+ a[3] = (p - 1) - (p - 2); /* { dg-bogus "integer overflow in
expression" } */
+ return b + c + d + e;
+}
Jakub
