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

[Tamar Christina <Tamar.Christina@arm.com>]

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Hi all,

Here's a new version of the patch.

> >>> " If an exceptional condition occurs during the evaluation of an
> >>> expression
> >> (that is, if the result is not mathematically defined or not in the
> >> range of representable values for its type), the behavior is undefined."
> >>>
> >>> So it should still be acceptable to do in this case.
> >>
> >> -fwrapv
> >
> > If I understand correctly, you're happy with this is I guard it on ! flag_wrapv ?
> 
> I did some more digging.  Right shift of a negative value is IMP_DEF (not
> UNDEF - this keeps catching me out).  So yes, wrapping this with !wrapv
> would address my concern.
> 
> I've not reviewed the patch itself, though.  I've never even written a patch
> for match.pd, so don't feel qualified to do that.

No problem, thanks for catching this! I'm sure one of the Richards will review it when
they have a chance.

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.target/aarch64/signbit-1.c: New test.

--- inline copy of patch ---

diff --git a/gcc/match.pd b/gcc/match.pd
index 7d2a24dbc5e9644a09968f877e12a824d8ba1caa..3d48eda826f889483a83267409c3f278ee907b57 100644
--- a/gcc/match.pd
+++ b/gcc/match.pd
@@ -826,6 +826,38 @@ 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 (!flag_wrapv)
+    (with { tree ctype = TREE_TYPE (@0);
+	    tree stype = TREE_TYPE (@1);
+	    tree bt = truth_type_for (ctype); }
+     (switch
+      /* Handle scalar case.  */
+      (if (INTEGRAL_TYPE_P (ctype)
+	   && !VECTOR_TYPE_P (ctype)
+	   && !TYPE_UNSIGNED (ctype)
+	   && canonicalize_math_after_vectorization_p ()
+	   && wi::eq_p (wi::to_wide (@1), TYPE_PRECISION (stype) - 1))
+       (convert:bt (gt:bt @0 { build_zero_cst (stype); })))
+      /* Handle vector case with a scalar immediate.  */
+      (if (VECTOR_INTEGER_TYPE_P (ctype)
+	   && !VECTOR_TYPE_P (stype)
+	   && !TYPE_UNSIGNED (ctype)
+           && wi::eq_p (wi::to_wide (@1), TYPE_PRECISION (stype) - 1))
+       (convert:bt (gt:bt @0 { build_zero_cst (ctype); })))
+      /* Handle vector case with a vector immediate.   */
+      (if (VECTOR_INTEGER_TYPE_P (ctype)
+	   && VECTOR_TYPE_P (stype)
+	   && !TYPE_UNSIGNED (ctype)
+	   && uniform_vector_p (@1))
+       (with { tree cst = vector_cst_elt (@1, 0);
+	       tree t = TREE_TYPE (cst); }
+        (if (wi::eq_p (wi::to_wide (cst), TYPE_PRECISION (t) - 1))
+         (convert:bt (gt:bt @0 { build_zero_cst (ctype); }))))))))))
+
 /* 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.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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diff --git a/gcc/match.pd b/gcc/match.pd
index 7d2a24dbc5e9644a09968f877e12a824d8ba1caa..3d48eda826f889483a83267409c3f278ee907b57 100644
--- a/gcc/match.pd
+++ b/gcc/match.pd
@@ -826,6 +826,38 @@ 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 (!flag_wrapv)
+    (with { tree ctype = TREE_TYPE (@0);
+	    tree stype = TREE_TYPE (@1);
+	    tree bt = truth_type_for (ctype); }
+     (switch
+      /* Handle scalar case.  */
+      (if (INTEGRAL_TYPE_P (ctype)
+	   && !VECTOR_TYPE_P (ctype)
+	   && !TYPE_UNSIGNED (ctype)
+	   && canonicalize_math_after_vectorization_p ()
+	   && wi::eq_p (wi::to_wide (@1), TYPE_PRECISION (stype) - 1))
+       (convert:bt (gt:bt @0 { build_zero_cst (stype); })))
+      /* Handle vector case with a scalar immediate.  */
+      (if (VECTOR_INTEGER_TYPE_P (ctype)
+	   && !VECTOR_TYPE_P (stype)
+	   && !TYPE_UNSIGNED (ctype)
+           && wi::eq_p (wi::to_wide (@1), TYPE_PRECISION (stype) - 1))
+       (convert:bt (gt:bt @0 { build_zero_cst (ctype); })))
+      /* Handle vector case with a vector immediate.   */
+      (if (VECTOR_INTEGER_TYPE_P (ctype)
+	   && VECTOR_TYPE_P (stype)
+	   && !TYPE_UNSIGNED (ctype)
+	   && uniform_vector_p (@1))
+       (with { tree cst = vector_cst_elt (@1, 0);
+	       tree t = TREE_TYPE (cst); }
+        (if (wi::eq_p (wi::to_wide (cst), TYPE_PRECISION (t) - 1))
+         (convert:bt (gt:bt @0 { build_zero_cst (ctype); }))))))))))
+
 /* 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.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 } } */