[PATCH]middle-end convert negate + right shift into compare greater.

Tamar Christina Tamar.Christina@arm.com
Wed Nov 3 13:21:19 GMT 2021


Hi,

I have addressed all the feedback and updated patch attached:

Bootstrapped Regtested on aarch64-none-linux-gnu,
x86_64-pc-linux-gnu and no regressions.

Ok for master?

Thanks,
Tamar

gcc/ChangeLog:

	* match.pd: New negate+shift pattern.

gcc/testsuite/ChangeLog:

	* gcc.dg/signbit-2.c: New test.
	* gcc.dg/signbit-3.c: New test.
	* gcc.dg/signbit-4.c: New test.
	* gcc.dg/signbit-5.c: New test.
	* gcc.dg/signbit-6.c: New test.
	* gcc.target/aarch64/signbit-1.c: New test.

--- inline copy of patch ---

diff --git a/gcc/match.pd b/gcc/match.pd
index 65a6591f75c03333602147bbdf6d59f9ccd4b1e5..fe93500d22e2388889c8c9faf4c58cee95dec7f9 100644
--- a/gcc/match.pd
+++ b/gcc/match.pd
@@ -38,7 +38,8 @@ along with GCC; see the file COPYING3.  If not see
    uniform_integer_cst_p
    HONOR_NANS
    uniform_vector_p
-   bitmask_inv_cst_vector_p)
+   bitmask_inv_cst_vector_p
+   expand_vec_cmp_expr_p)
 
 /* Operator lists.  */
 (define_operator_list tcc_comparison
@@ -832,6 +833,38 @@ DEFINE_INT_AND_FLOAT_ROUND_FN (RINT)
     { tree utype = unsigned_type_for (type); }
     (convert (rshift (lshift (convert:utype @0) @2) @3))))))
 
+/* Fold (-x >> C) into -(x > 0) where C = precision(type) - 1.  */
+(for cst (INTEGER_CST VECTOR_CST)
+ (simplify
+  (rshift (negate:s @0) cst@1)
+   (if (!TYPE_UNSIGNED (type)
+        && TYPE_OVERFLOW_UNDEFINED (type))
+    (with { tree stype = TREE_TYPE (@1);
+	    tree bt = truth_type_for (type);
+	    tree zeros = build_zero_cst (type); }
+     (switch
+      /* Handle scalar case.  */
+      (if (INTEGRAL_TYPE_P (type)
+	   /* If we apply the rule to the scalar type before vectorization
+	      we will enforce the result of the comparison being a bool
+	      which will require an extra AND on the result that will be
+	      indistinguishable from when the user did actually want 0
+	      or 1 as the result so it can't be removed.  */
+	   && canonicalize_math_after_vectorization_p ()
+	   && wi::eq_p (wi::to_wide (@1), TYPE_PRECISION (type) - 1))
+       (negate (convert (gt @0 { zeros; }))))
+      /* Handle vector case.  */
+      (if (VECTOR_INTEGER_TYPE_P (type)
+	   /* First check whether the target has the same mode for vector
+	      comparison results as it's operands do.  */
+	   && TYPE_MODE (bt) == TYPE_MODE (type)
+	   /* Then check to see if the target is able to expand the comparison
+	      with the given type later on, otherwise we may ICE.  */
+	   && expand_vec_cmp_expr_p (type, bt, { GT_EXPR }))
+       (with { tree cst = uniform_integer_cst_p (@1); }
+	(if (cst && wi::eq_p (wi::to_wide (cst), element_precision (type) - 1))
+	 (view_convert (gt:bt @0 { zeros; }))))))))))
+
 /* Fold (C1/X)*C2 into (C1*C2)/X.  */
 (simplify
  (mult (rdiv@3 REAL_CST@0 @1) REAL_CST@2)
diff --git a/gcc/testsuite/gcc.dg/signbit-2.c b/gcc/testsuite/gcc.dg/signbit-2.c
new file mode 100644
index 0000000000000000000000000000000000000000..fc0157cbc5c7996b481f2998bc30176c96a669bb
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/signbit-2.c
@@ -0,0 +1,19 @@
+/* { dg-do assemble } */
+/* { dg-options "-O3 --save-temps -fdump-tree-optimized" } */
+
+#include <stdint.h>
+
+void fun1(int32_t *x, int n)
+{
+    for (int i = 0; i < (n & -16); i++)
+      x[i] = (-x[i]) >> 31;
+}
+
+void fun2(int32_t *x, int n)
+{
+    for (int i = 0; i < (n & -16); i++)
+      x[i] = (-x[i]) >> 30;
+}
+
+/* { dg-final { scan-tree-dump-times {\s+>\s+\{ 0, 0, 0, 0 \}} 1 optimized } } */
+/* { dg-final { scan-tree-dump-not {\s+>>\s+31} optimized } } */
diff --git a/gcc/testsuite/gcc.dg/signbit-3.c b/gcc/testsuite/gcc.dg/signbit-3.c
new file mode 100644
index 0000000000000000000000000000000000000000..19e9c06c349b3287610f817628f00938ece60bf7
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/signbit-3.c
@@ -0,0 +1,13 @@
+/* { dg-do assemble } */
+/* { dg-options "-O1 --save-temps -fdump-tree-optimized" } */
+
+#include <stdint.h>
+
+void fun1(int32_t *x, int n)
+{
+    for (int i = 0; i < (n & -16); i++)
+      x[i] = (-x[i]) >> 31;
+}
+
+/* { dg-final { scan-tree-dump-times {\s+>\s+0;} 1 optimized } } */
+/* { dg-final { scan-tree-dump-not {\s+>>\s+31} optimized } } */
diff --git a/gcc/testsuite/gcc.dg/signbit-4.c b/gcc/testsuite/gcc.dg/signbit-4.c
new file mode 100644
index 0000000000000000000000000000000000000000..bc459ba60a760bdf49e94dbec762f378c24fe9b5
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/signbit-4.c
@@ -0,0 +1,65 @@
+/* { dg-do run } */
+/* { dg-options "-O1 -fwrapv" } */
+
+#include <stdint.h>
+#include <limits.h>
+#include <stdio.h>
+
+#ifndef N
+#define N 65
+#endif
+
+#ifndef TYPE
+#define TYPE int32_t
+#endif
+
+#ifndef DEBUG
+#define DEBUG 1
+#endif
+
+#define BASE ((TYPE) -1 < 0 ? -126 : 4)
+
+__attribute__ ((noinline, noipa))
+void fun1(TYPE *x, int n)
+{
+    for (int i = 0; i < n; i++)
+      x[i] = (-x[i]) >> 31;
+}
+
+__attribute__ ((noinline, noipa, optimize("O0")))
+void fun2(TYPE *x, int n)
+{
+    for (int i = 0; i < n; i++)
+      x[i] = (-x[i]) >> 31;
+}
+
+int main ()
+{
+  TYPE a[N];
+  TYPE b[N];
+
+  a[0] = INT_MIN;
+  b[0] = INT_MIN;
+
+  for (int i = 1; i < N; ++i)
+    {
+      a[i] = BASE + i * 13;
+      b[i] = BASE + i * 13;
+      if (DEBUG)
+        printf ("%d: 0x%x\n", i, a[i]);
+    }
+
+  fun1 (a, N);
+  fun2 (b, N);
+
+  for (int i = 0; i < N; ++i)
+    {
+      if (DEBUG)
+        printf ("%d = 0x%x == 0x%x\n", i, a[i], b[i]);
+
+      if (a[i] != b[i])
+        __builtin_abort ();
+    }
+  return 0;
+}
+
diff --git a/gcc/testsuite/gcc.dg/signbit-5.c b/gcc/testsuite/gcc.dg/signbit-5.c
new file mode 100644
index 0000000000000000000000000000000000000000..22a92704773e3282759524b74d35196a477d43dd
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/signbit-5.c
@@ -0,0 +1,65 @@
+/* { dg-do run } */
+/* { dg-options "-O3" } */
+
+#include <stdint.h>
+#include <limits.h>
+#include <stdio.h>
+
+#ifndef N
+#define N 65
+#endif
+
+#ifndef TYPE
+#define TYPE int32_t
+#endif
+
+#ifndef DEBUG
+#define DEBUG 1
+#endif
+
+#define BASE ((TYPE) -1 < 0 ? -126 : 4)
+
+__attribute__ ((noinline, noipa))
+void fun1(TYPE *x, int n)
+{
+    for (int i = 0; i < n; i++)
+      x[i] = (-x[i]) >> 31;
+}
+
+__attribute__ ((noinline, noipa, optimize("O1")))
+void fun2(TYPE *x, int n)
+{
+    for (int i = 0; i < n; i++)
+      x[i] = (-x[i]) >> 31;
+}
+
+int main ()
+{
+  TYPE a[N];
+  TYPE b[N];
+
+  a[0] = INT_MIN;
+  b[0] = INT_MIN;
+
+  for (int i = 1; i < N; ++i)
+    {
+      a[i] = BASE + i * 13;
+      b[i] = BASE + i * 13;
+      if (DEBUG)
+        printf ("%d: 0x%x\n", i, a[i]);
+    }
+
+  fun1 (a, N);
+  fun2 (b, N);
+
+  for (int i = 0; i < N; ++i)
+    {
+      if (DEBUG)
+        printf ("%d = 0x%x == 0x%x\n", i, a[i], b[i]);
+
+      if (a[i] != b[i])
+        __builtin_abort ();
+    }
+  return 0;
+}
+
diff --git a/gcc/testsuite/gcc.dg/signbit-6.c b/gcc/testsuite/gcc.dg/signbit-6.c
new file mode 100644
index 0000000000000000000000000000000000000000..da186624cfa057dfc3780c8af4f6b1335ba07e7e
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/signbit-6.c
@@ -0,0 +1,72 @@
+/* { dg-do run } */
+/* { dg-options "-O1" } */
+
+#include <stdint.h>
+#include <limits.h>
+#include <stdio.h>
+
+#ifndef N
+#define N 65
+#endif
+
+#ifndef TYPE
+#define TYPE int32_t
+#endif
+
+#ifndef DEBUG
+#define DEBUG 1
+#endif
+
+#define BASE ((TYPE) -1 < 0 ? -126 : 4)
+
+__attribute__ ((noinline, noipa))
+void fun1(TYPE *x, int n)
+{
+    for (int i = 0; i < n; i++)
+      x[i] = (-x[i]) >> 31;
+}
+
+__attribute__ ((noinline, noipa, optimize("O0")))
+void fun2(TYPE *x, int n)
+{
+    for (int i = 0; i < n; i++)
+      x[i] = (-x[i]) >> 31;
+}
+
+int main ()
+{
+  TYPE a[N];
+  TYPE b[N];
+
+  a[0] = INT_MIN;
+  b[0] = INT_MIN;
+
+  for (int i = 1; i < N; ++i)
+    {
+      a[i] = BASE + i * 13;
+      b[i] = BASE + i * 13;
+      if (DEBUG)
+        printf ("%d: 0x%x\n", i, a[i]);
+    }
+
+  fun1 (a, N);
+  fun2 (b, N);
+
+  if (DEBUG)
+    printf ("%d = 0x%x == 0x%x\n", 0, a[0], b[0]);
+
+  if (a[0] != 0x0 || b[0] != -1)
+        __builtin_abort ();
+
+
+  for (int i = 1; i < N; ++i)
+    {
+      if (DEBUG)
+        printf ("%d = 0x%x == 0x%x\n", i, a[i], b[i]);
+
+      if (a[i] != b[i])
+        __builtin_abort ();
+    }
+  return 0;
+}
+
diff --git a/gcc/testsuite/gcc.target/aarch64/signbit-1.c b/gcc/testsuite/gcc.target/aarch64/signbit-1.c
new file mode 100644
index 0000000000000000000000000000000000000000..3ebfb0586f37de29cf58635b27fe48503714447e
--- /dev/null
+++ b/gcc/testsuite/gcc.target/aarch64/signbit-1.c
@@ -0,0 +1,18 @@
+/* { dg-do assemble } */
+/* { dg-options "-O3 --save-temps" } */
+
+#include <stdint.h>
+
+void fun1(int32_t *x, int n)
+{
+    for (int i = 0; i < (n & -16); i++)
+      x[i] = (-x[i]) >> 31;
+}
+
+void fun2(int32_t *x, int n)
+{
+    for (int i = 0; i < (n & -16); i++)
+      x[i] = (-x[i]) >> 30;
+}
+
+/* { dg-final { scan-assembler-times {\tcmgt\t} 1 } } */
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