Hello,
the first part is something that was discussed last stage3, and Jakub
argued in favor of single_use. The second part is probably less useful, it
notices that if we manually check for overflow using the result of
IFN_*_OVERFLOW, then we might as well read that information from the
result of that function.
Bootstrap+regtest on powerpc64le-unknown-linux-gnu. (hmm, I probably
should have done it on x86_64 instead, I don't know if the ppc backend has
implemented the overflow functions recently)
2016-04-25 Marc Glisse <marc.gli...@inria.fr>
gcc/
* match.pd (A - B > A, A + B < A): New transformations.
gcc/testsuite/
* gcc.dg/tree-ssa/overflow-2.c: New testcase.
* gcc.dg/tree-ssa/minus-ovf.c: Likewise.
--
Marc GlisseIndex: trunk-ovf2/gcc/match.pd
===================================================================
--- trunk-ovf2/gcc/match.pd (revision 235371)
+++ trunk-ovf2/gcc/match.pd (working copy)
@@ -3071,10 +3071,60 @@ DEFINE_INT_AND_FLOAT_ROUND_FN (RINT)
(simplify
/* signbit(x) -> 0 if x is nonnegative. */
(SIGNBIT tree_expr_nonnegative_p@0)
{ integer_zero_node; })
(simplify
/* signbit(x) -> x<0 if x doesn't have signed zeros. */
(SIGNBIT @0)
(if (!HONOR_SIGNED_ZEROS (@0))
(convert (lt @0 { build_real (TREE_TYPE (@0), dconst0); }))))
+
+/* To detect overflow in unsigned A - B, A < B is simpler than A - B > A.
+ However, the detection logic for SUB_OVERFLOW in tree-ssa-math-opts.c
+ expects the long form, so we restrict the transformation for now. */
+(for cmp (gt le)
+ (simplify
+ (cmp (minus@2 @0 @1) @0)
+ (if (single_use (@2)
+ && ANY_INTEGRAL_TYPE_P (TREE_TYPE (@0))
+ && TYPE_UNSIGNED (TREE_TYPE (@0))
+ && TYPE_OVERFLOW_WRAPS (TREE_TYPE (@0)))
+ (cmp @1 @0))))
+(for cmp (lt ge)
+ (simplify
+ (cmp @0 (minus@2 @0 @1))
+ (if (single_use (@2)
+ && ANY_INTEGRAL_TYPE_P (TREE_TYPE (@0))
+ && TYPE_UNSIGNED (TREE_TYPE (@0))
+ && TYPE_OVERFLOW_WRAPS (TREE_TYPE (@0)))
+ (cmp @0 @1))))
+
+/* Testing for overflow is unnecessary if we already know the result. */
+/* A < A - B */
+(for cmp (lt ge)
+ out (ne eq)
+ (simplify
+ (cmp @0 (realpart (IFN_SUB_OVERFLOW@2 @0 @1)))
+ (if (TYPE_UNSIGNED (TREE_TYPE (@0)))
+ (out (imagpart @2) { build_zero_cst (TREE_TYPE (@0)); }))))
+/* A - B > A */
+(for cmp (gt le)
+ out (ne eq)
+ (simplify
+ (cmp (realpart (IFN_SUB_OVERFLOW@2 @0 @1)) @0)
+ (if (TYPE_UNSIGNED (TREE_TYPE (@0)))
+ (out (imagpart @2) { build_zero_cst (TREE_TYPE (@0)); }))))
+/* A + B < A */
+(for cmp (lt ge)
+ out (ne eq)
+ (simplify
+ (cmp (realpart (IFN_ADD_OVERFLOW:c@2 @0 @1)) @0)
+ (if (TYPE_UNSIGNED (TREE_TYPE (@0)))
+ (out (imagpart @2) { build_zero_cst (TREE_TYPE (@0)); }))))
+/* A > A + B */
+(for cmp (gt le)
+ out (ne eq)
+ (simplify
+ (cmp @0 (realpart (IFN_ADD_OVERFLOW:c@2 @0 @1)))
+ (if (TYPE_UNSIGNED (TREE_TYPE (@0)))
+ (out (imagpart @2) { build_zero_cst (TREE_TYPE (@0)); }))))
Index: trunk-ovf2/gcc/testsuite/gcc.dg/tree-ssa/minus-ovf.c
===================================================================
--- trunk-ovf2/gcc/testsuite/gcc.dg/tree-ssa/minus-ovf.c (revision 0)
+++ trunk-ovf2/gcc/testsuite/gcc.dg/tree-ssa/minus-ovf.c (working copy)
@@ -0,0 +1,24 @@
+/* { dg-do compile } */
+/* { dg-options "-O -fdump-tree-optimized" } */
+
+int f(unsigned a, unsigned b) {
+ unsigned remove = a - b;
+ return remove > a;
+}
+
+int g(unsigned a, unsigned b) {
+ unsigned remove = a - b;
+ return remove <= a;
+}
+
+int h(unsigned a, unsigned b) {
+ unsigned remove = a - b;
+ return a < remove;
+}
+
+int i(unsigned a, unsigned b) {
+ unsigned remove = a - b;
+ return a >= remove;
+}
+
+/* { dg-final { scan-tree-dump-not "remove" "optimized" } } */
Index: trunk-ovf2/gcc/testsuite/gcc.dg/tree-ssa/overflow-2.c
===================================================================
--- trunk-ovf2/gcc/testsuite/gcc.dg/tree-ssa/overflow-2.c (revision 0)
+++ trunk-ovf2/gcc/testsuite/gcc.dg/tree-ssa/overflow-2.c (working copy)
@@ -0,0 +1,68 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -fdump-tree-optimized-raw" } */
+
+int carry;
+int f(unsigned a, unsigned b) {
+ unsigned r;
+ carry = __builtin_sub_overflow(a, b, &r);
+ return r > a;
+}
+int g(unsigned a, unsigned b) {
+ unsigned r;
+ carry = __builtin_sub_overflow(a, b, &r);
+ return a < r;
+}
+int h(unsigned a, unsigned b) {
+ unsigned r;
+ carry = __builtin_sub_overflow(a, b, &r);
+ return r <= a;
+}
+int i(unsigned a, unsigned b) {
+ unsigned r;
+ carry = __builtin_sub_overflow(a, b, &r);
+ return a >= r;
+}
+int j(unsigned a, unsigned b) {
+ unsigned r;
+ carry = __builtin_add_overflow(a, b, &r);
+ return r < a;
+}
+int j2(unsigned a, unsigned b) {
+ unsigned r;
+ carry = __builtin_add_overflow(a, b, &r);
+ return r < b;
+}
+int k(unsigned a, unsigned b) {
+ unsigned r;
+ carry = __builtin_add_overflow(a, b, &r);
+ return a > r;
+}
+int k2(unsigned a, unsigned b) {
+ unsigned r;
+ carry = __builtin_add_overflow(a, b, &r);
+ return b > r;
+}
+int l(unsigned a, unsigned b) {
+ unsigned r;
+ carry = __builtin_add_overflow(a, b, &r);
+ return r >= a;
+}
+int l2(unsigned a, unsigned b) {
+ unsigned r;
+ carry = __builtin_add_overflow(a, b, &r);
+ return r >= b;
+}
+int m(unsigned a, unsigned b) {
+ unsigned r;
+ carry = __builtin_add_overflow(a, b, &r);
+ return a <= r;
+}
+int m2(unsigned a, unsigned b) {
+ unsigned r;
+ carry = __builtin_add_overflow(a, b, &r);
+ return b <= r;
+}
+
+/* { dg-final { scan-tree-dump-not "(le|lt|ge|gt)_expr" "optimized" } } */
+/* { dg-final { scan-tree-dump-times "ADD_OVERFLOW" 8 "optimized" } } */
+/* { dg-final { scan-tree-dump-times "SUB_OVERFLOW" 4 "optimized" } } */
