tree-optimization/116024 - simplify some cases of X +- C1 cmp C2

Whenever C1 and C2 are integer constants, X is of a wrapping type, and
cmp is a relational operator, the expression X +- C1 cmp C2 can be
simplified in the following cases:

(a) If cmp is <= and C2 -+ C1 == +INF(1), we can transform the initial
comparison in the following way:
   X +- C1 <= C2
   -INF <= X +- C1 <= C2 (add left hand side which holds for any X, C1)
   -INF -+ C1 <= X <= C2 -+ C1 (add -+C1 to all 3 expressions)
   -INF -+ C1 <= X <= +INF (due to (1))
   -INF -+ C1 <= X (eliminate the right hand side since it holds for any X)

(b) By analogy, if cmp if >= and C2 -+ C1 == -INF(1), use the following
sequence of transformations:

   X +- C1 >= C2
   +INF >= X +- C1 >= C2 (add left hand side which holds for any X, C1)
   +INF -+ C1 >= X >= C2 -+ C1 (add -+C1 to all 3 expressions)
   +INF -+ C1 >= X >= -INF (due to (1))
   +INF -+ C1 >= X (eliminate the right hand side since it holds for any X)

(c) The > and < cases are negations of (a) and (b), respectively.

This transformation allows to occasionally save add / sub instructions,
for instance the expression

3 + (uint32_t)f() < 2

compiles to

cmn     w0, #4
cset    w0, ls

instead of

add     w0, w0, 3
cmp     w0, 2
cset    w0, ls

on aarch64.

Testcases that go together with this patch have been split into two
separate files, one containing testcases for unsigned variables and the
other for wrapping signed ones (and thus compiled with -fwrapv).
Additionally, one aarch64 test has been adjusted since the patch has
caused the generated code to change from

cmn     w0, #2
csinc   w0, w1, wzr, cc   (x < -2)

to

cmn     w0, #3
csinc   w0, w1, wzr, cs   (x <= -3)

This patch has been bootstrapped and regtested on aarch64, x86_64, and
i386, and additionally regtested on riscv32.

gcc/ChangeLog:

	PR tree-optimization/116024
	* match.pd: New transformation around integer comparison.

gcc/testsuite/ChangeLog:

	* gcc.dg/tree-ssa/pr116024-2.c: New test.
	* gcc.dg/tree-ssa/pr116024-2-fwrapv.c: Ditto.
	* gcc.target/aarch64/gtu_to_ltu_cmp_1.c: Adjust.

diff --git a/gcc/match.pd b/gcc/match.pd
index baa6d2f5fd7d35fd98e7c3505e8a33dbed226e3a..e73bb7e2109b8238ab39e09c97b9603217240ebe 100644 (file)
--- a/gcc/match.pd
+++ b/gcc/match.pd
@@ -9030,6 +9030,7 @@ DEFINE_INT_AND_FLOAT_ROUND_FN (RINT)
        (cmp @0 { TREE_OVERFLOW (res)
                 ? drop_tree_overflow (res) : res; }))))))))
 (for cmp (lt le gt ge)
+     rcmp (gt ge lt le)
  (for op (plus minus)
       rop (minus plus)
   (simplify
@@ -9057,7 +9058,47 @@ DEFINE_INT_AND_FLOAT_ROUND_FN (RINT)
                                  "X cmp C2 -+ C1"),
                                 WARN_STRICT_OVERFLOW_COMPARISON);
        }
-       (cmp @0 { res; })))))))))
+       (cmp @0 { res; })))))
+/* For wrapping types, simplify the following cases of X +- C1 CMP C2:
+
+   (a) If CMP is <= and C2 -+ C1 == +INF (1), simplify to X >= -INF -+ C1
+       by observing the following:
+
+       X +- C1 <= C2
+  ==>  -INF <= X +- C1 <= C2 (add left hand side which holds for any X, C1)
+  ==>  -INF -+ C1 <= X <= C2 -+ C1 (add -+C1 to all 3 expressions)
+  ==>  -INF -+ C1 <= X <= +INF (due to (1))
+  ==>  -INF -+ C1 <= X (eliminate the right hand side since it holds for any X)
+
+    (b) Similarly, if CMP is >= and C2 -+ C1 == -INF (1):
+
+       X +- C1 >= C2
+  ==>  +INF >= X +- C1 >= C2 (add left hand side which holds for any X, C1)
+  ==>  +INF -+ C1 >= X >= C2 -+ C1 (add -+C1 to all 3 expressions)
+  ==>  +INF -+ C1 >= X >= -INF (due to (1))
+  ==>  +INF -+ C1 >= X (eliminate the right hand side since it holds for any X)
+
+    (c) The > and < cases are negations of (a) and (b), respectively.  */
+   (if (TYPE_OVERFLOW_WRAPS (TREE_TYPE (@0)))
+     (with
+       {
+       wide_int max = wi::max_value (TREE_TYPE (@0));
+       wide_int min = wi::min_value (TREE_TYPE (@0));
+
+       wide_int c2 = rop == PLUS_EXPR
+                             ? wi::add (wi::to_wide (@2), wi::to_wide (@1))
+                             : wi::sub (wi::to_wide (@2), wi::to_wide (@1));
+       }
+       (if (((cmp == LE_EXPR || cmp == GT_EXPR) && wi::eq_p (c2, max))
+           || ((cmp == LT_EXPR || cmp == GE_EXPR) && wi::eq_p (c2, min)))
+         (with
+          {
+            wide_int c1 = rop == PLUS_EXPR
+                          ? wi::add (wi::bit_not (c2), wi::to_wide (@1))
+                          : wi::sub (wi::bit_not (c2), wi::to_wide (@1));
+            tree c1_cst = wide_int_to_tree (TREE_TYPE (@0), c1);
+          }
+          (rcmp @0 { c1_cst; })))))))))
 
 /* Invert sign of X in comparisons of the form C1 - X CMP C2.  */
 

diff --git a/gcc/testsuite/gcc.dg/tree-ssa/pr116024-2-fwrapv.c b/gcc/testsuite/gcc.dg/tree-ssa/pr116024-2-fwrapv.c
new file mode 100644 (file)
index 0000000..b9e88ba
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/tree-ssa/pr116024-2-fwrapv.c
@@ -0,0 +1,38 @@
+/* PR tree-optimization/116024 */
+/* { dg-do compile } */
+/* { dg-options "-O1 -fdump-tree-forwprop1-details -fwrapv" } */
+
+#include <stdint.h>
+#include <limits.h>
+
+uint32_t f(void);
+
+int32_t i3(void)
+{
+  int32_t l = -10 + (int32_t)f();
+  return l <= INT32_MAX - 10; // f() >= INT32_MIN + 10
+}
+
+int32_t i3a(void)
+{
+  int32_t l = -20 + (int32_t)f();
+  return l < INT32_MAX - 19; // f() > INT32_MAX + 20
+}
+
+int32_t i3b(void)
+{
+  int32_t l = 30 + (int32_t)f();
+  return l >= INT32_MIN + 30; // f() <= INT32_MAX - 30
+}
+
+int32_t i3c(void)
+{
+  int32_t l = 40 + (int32_t)f();
+  return l > INT32_MIN + 39; // f() < INT32_MIN - 40
+}
+
+/* { dg-final { scan-tree-dump-times "Removing dead stmt:.*? \\+" 4 "forwprop1" } } */
+/* { dg-final { scan-tree-dump-times "gimple_simplified to.* >= -2147483638" 1 "forwprop1" } } */
+/* { dg-final { scan-tree-dump-times "gimple_simplified to.* >= -2147483628" 1 "forwprop1" } } */
+/* { dg-final { scan-tree-dump-times "gimple_simplified to.* <= 2147483617" 1 "forwprop1" } } */
+/* { dg-final { scan-tree-dump-times "gimple_simplified to.* <= 2147483607" 1 "forwprop1" } } */

diff --git a/gcc/testsuite/gcc.dg/tree-ssa/pr116024-2.c b/gcc/testsuite/gcc.dg/tree-ssa/pr116024-2.c
new file mode 100644 (file)
index 0000000..f7ff077
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/tree-ssa/pr116024-2.c
@@ -0,0 +1,37 @@
+/* PR tree-optimization/116024 */
+/* { dg-do compile } */
+/* { dg-options "-O1 -fdump-tree-forwprop1-details" } */
+
+#include <stdint.h>
+
+uint32_t f(void);
+
+int32_t i3(void)
+{
+  uint32_t l = 10 + (uint32_t)f();
+  return l <= 9; // f() >= -10u
+}
+
+int32_t i3a(void)
+{
+  uint32_t l = 20 + (uint32_t)f();
+  return l < 20; // f() > -21u
+}
+
+int32_t i3b(void)
+{
+  uint32_t l = 30 + (uint32_t)f();
+  return l >= 30; // f() <= -31u
+}
+
+int32_t i3c(void)
+{
+  uint32_t l = 40 + (uint32_t)f();
+  return l > 39; // f() < -39u
+}
+
+/* { dg-final { scan-tree-dump-times "Removing dead stmt:.*? \\+" 4 "forwprop1" } } */
+/* { dg-final { scan-tree-dump-times "gimple_simplified to.* > 4294967285" 1 "forwprop1" } } */
+/* { dg-final { scan-tree-dump-times "gimple_simplified to.* > 4294967275" 1 "forwprop1" } } */
+/* { dg-final { scan-tree-dump-times "gimple_simplified to.* <= 4294967265" 1 "forwprop1" } } */
+/* { dg-final { scan-tree-dump-times "gimple_simplified to.* <= 4294967255" 1 "forwprop1" } } */

diff --git a/gcc/testsuite/gcc.target/aarch64/gtu_to_ltu_cmp_1.c b/gcc/testsuite/gcc.target/aarch64/gtu_to_ltu_cmp_1.c
index 81c536c90afe38932c48ed0af24f55e73eeff80e..bfcec6719deb9ce6907055ba3d3b2d2075a8e8b7 100644 (file)
--- a/gcc/testsuite/gcc.target/aarch64/gtu_to_ltu_cmp_1.c
+++ b/gcc/testsuite/gcc.target/aarch64/gtu_to_ltu_cmp_1.c
@@ -10,4 +10,4 @@ f1 (int x, int t)
   return t;
 }
 
-/* { dg-final { scan-assembler-times "cmn\\tw\[0-9\]+, #2" 1 } } */
+/* { dg-final { scan-assembler-times "cmn\\tw\[0-9\]+, #3" 1 } } */