Simplify floating point comparisons

This patch implements some of the optimizations discussed in PR71026.

Simplify (C / x >= 0.0) into x >= 0.0 with -funsafe-math-optimizations
(since C / x can underflow to zero if x is huge, it's not safe otherwise).
If C is negative the comparison is reversed.

Simplify (x * C1) > C2 into x > (C2 / C1) with -funsafe-math-optimizations.
If C1 is negative the comparison is reversed.

    gcc/
	PR 71026/tree-optimization
	* match.pd: Simplify floating point comparisons.

    gcc/testsuite/
	PR 71026/tree-optimization
	* gcc.dg/div-cmp-1.c: New test.
	* gcc.dg/div-cmp-2.c: New test.

Co-Authored-By: Jackson Woodruff <jackson.woodruff@arm.com>

From-SVN: r266142

5 files changed, 101 insertions, 0 deletions

diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index 6f9b26e..47d4930 100644
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,3 +1,9 @@
+2018-11-14  Wilco Dijkstra  <wdijkstr@arm.com>  
+	    Jackson Woodruff  <jackson.woodruff@arm.com>
+
+	PR 71026/tree-optimization
+	* match.pd: Simplify floating point comparisons.
+
 2018-11-14  Jakub Jelinek  <jakub@redhat.com>
 
 	PR rtl-optimization/87817
diff --git a/gcc/match.pd b/gcc/match.pd
index d47249a..e9f9e0c 100644
--- a/gcc/match.pd
+++ b/gcc/match.pd
@@ -405,6 +405,21 @@ DEFINE_INT_AND_FLOAT_ROUND_FN (RINT)
  (rdiv @0 (negate @1))
  (rdiv (negate @0) @1))
 
+(if (flag_unsafe_math_optimizations)
+ /* Simplify (C / x op 0.0) to x op 0.0 for C != 0, C != Inf/Nan.
+    Since C / x may underflow to zero, do this only for unsafe math.  */
+ (for op (lt le gt ge)
+      neg_op (gt ge lt le)
+  (simplify
+   (op (rdiv REAL_CST@0 @1) real_zerop@2)
+   (if (!HONOR_SIGNED_ZEROS (@1) && !HONOR_INFINITIES (@1))
+    (switch
+     (if (real_less (&dconst0, TREE_REAL_CST_PTR (@0)))
+      (op @1 @2))
+     /* For C < 0, use the inverted operator.  */
+     (if (real_less (TREE_REAL_CST_PTR (@0), &dconst0))
+      (neg_op @1 @2)))))))
+
 /* Optimize (X & (-A)) / A where A is a power of 2, to X >> log2(A) */
 (for div (trunc_div ceil_div floor_div round_div exact_div)
  (simplify
@@ -4098,6 +4113,22 @@ DEFINE_INT_AND_FLOAT_ROUND_FN (RINT)
        (rdiv @2 @1))
    (rdiv (op @0 @2) @1)))
 
+ (for cmp (lt le gt ge)
+      neg_cmp (gt ge lt le)
+  /* Simplify (x * C1) cmp C2 -> x cmp (C2 / C1), where C1 != 0.  */
+  (simplify
+   (cmp (mult @0 REAL_CST@1) REAL_CST@2)
+   (with
+    { tree tem = const_binop (RDIV_EXPR, type, @2, @1); }
+    (if (tem
+	 && !(REAL_VALUE_ISINF (TREE_REAL_CST (tem))
+	      || (real_zerop (tem) && !real_zerop (@1))))
+     (switch
+      (if (real_less (&dconst0, TREE_REAL_CST_PTR (@1)))
+       (cmp @0 { tem; }))
+      (if (real_less (TREE_REAL_CST_PTR (@1), &dconst0))
+       (neg_cmp @0 { tem; })))))))
+
  /* Simplify sqrt(x) * sqrt(y) -> sqrt(x*y).  */
  (for root (SQRT CBRT)
   (simplify
diff --git a/gcc/testsuite/ChangeLog b/gcc/testsuite/ChangeLog
index 5f58860..e56706c 100644
--- a/gcc/testsuite/ChangeLog
+++ b/gcc/testsuite/ChangeLog
@@ -1,3 +1,10 @@
+2018-11-14  Wilco Dijkstra  <wdijkstr@arm.com>  
+	    Jackson Woodruff  <jackson.woodruff@arm.com>
+
+	PR 71026/tree-optimization
+	* gcc.dg/div-cmp-1.c: New test.
+	* gcc.dg/div-cmp-2.c: New test.
+
 2018-11-14  Jakub Jelinek  <jakub@redhat.com>
 
 	PR other/88007
diff --git a/gcc/testsuite/gcc.dg/div-cmp-1.c b/gcc/testsuite/gcc.dg/div-cmp-1.c
new file mode 100644
index 0000000..cd1a5cd
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/div-cmp-1.c
@@ -0,0 +1,29 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -funsafe-math-optimizations -fdump-tree-optimized-raw" } */
+
+int
+cmp_mul_1 (float x)
+{
+  return x * 3 <= 100;
+}
+
+int
+cmp_mul_2 (float x)
+{
+  return x * -5 > 100;
+}
+
+int
+div_cmp_1 (float x, float y)
+{
+  return x / 3 <= y;
+}
+
+int
+div_cmp_2 (float x, float y)
+{
+  return x / 3 <= 1;
+}
+
+/* { dg-final { scan-tree-dump-times "mult_expr" 1 "optimized" } } */
+/* { dg-final { scan-tree-dump-not "rdiv_expr" "optimized" } } */
diff --git a/gcc/testsuite/gcc.dg/div-cmp-2.c b/gcc/testsuite/gcc.dg/div-cmp-2.c
new file mode 100644
index 0000000..95e5400
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/div-cmp-2.c
@@ -0,0 +1,28 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -funsafe-math-optimizations -ffinite-math-only -fdump-tree-optimized-raw" } */
+
+int
+cmp_1 (float x)
+{
+  return 5 / x >= 0;
+}
+
+int
+cmp_2 (float x)
+{
+  return 1 / x <= 0;
+}
+
+int
+cmp_3 (float x)
+{
+  return -2 / x >= 0;
+}
+
+int
+cmp_4 (float x)
+{
+  return -5 / x <= 0;
+}
+
+/* { dg-final { scan-tree-dump-not "rdiv_expr" "optimized" } } */