diff --git a/gcc/match.pd b/gcc/match.pd
index 097ed2e5dff..a063a1577b5 100644
--- a/gcc/match.pd
+++ b/gcc/match.pd
@@ -4482,9 +4482,20 @@ DEFINE_INT_AND_FLOAT_ROUND_FN (RINT)
    /* a CMP (-0) -> a CMP 0  */
    (if (REAL_VALUE_MINUS_ZERO (TREE_REAL_CST (@1)))
     (cmp @0 { build_real (TREE_TYPE (@1), dconst0); }))
+   /* (-0) CMP b -> 0 CMP b.  */
+   (if (TREE_CODE (@0) == REAL_CST
+	&& REAL_VALUE_MINUS_ZERO (TREE_REAL_CST (@0)))
+    (cmp { build_real (TREE_TYPE (@0), dconst0); } @1))
    /* x != NaN is always true, other ops are always false.  */
    (if (REAL_VALUE_ISNAN (TREE_REAL_CST (@1))
-	&& ! HONOR_SNANS (@1))
+	&& !tree_expr_signaling_nan_p (@1)
+	&& !tree_expr_maybe_signaling_nan_p (@0))
+    { constant_boolean_node (cmp == NE_EXPR, type); })
+   /* NaN != y is always true, other ops are always false.  */
+   (if (TREE_CODE (@0) == REAL_CST
+	&& REAL_VALUE_ISNAN (TREE_REAL_CST (@0))
+        && !tree_expr_signaling_nan_p (@0)
+        && !tree_expr_signaling_nan_p (@1))
     { constant_boolean_node (cmp == NE_EXPR, type); })
    /* Fold comparisons against infinity.  */
    (if (REAL_VALUE_ISINF (TREE_REAL_CST (@1))
diff --git a/gcc/testsuite/c-c++-common/pr57371-4.c b/gcc/testsuite/c-c++-common/pr57371-4.c
index f43f7c22419..d938ecdd675 100644
--- a/gcc/testsuite/c-c++-common/pr57371-4.c
+++ b/gcc/testsuite/c-c++-common/pr57371-4.c
@@ -13,25 +13,25 @@ void nonfinite(unsigned short x) {
   {
     volatile int nonfinite_1;
     nonfinite_1 = (float) x > QNAN;
-    /* { dg-final { scan-tree-dump "nonfinite_1 = \\(float\\)" "original" } } */
+    /* { dg-final { scan-tree-dump "nonfinite_1 = 0" "original" } } */
   }
 
   {
     volatile int nonfinite_2;
     nonfinite_2 = (float) x >= QNAN;
-    /* { dg-final { scan-tree-dump "nonfinite_2 = \\(float\\)" "original" } } */
+    /* { dg-final { scan-tree-dump "nonfinite_2 = 0" "original" } } */
   }
 
   {
     volatile int nonfinite_3;
     nonfinite_3 = (float) x < QNAN;
-    /* { dg-final { scan-tree-dump "nonfinite_3 = \\(float\\)" "original" } } */
+    /* { dg-final { scan-tree-dump "nonfinite_3 = 0" "original" } } */
   }
 
   {
     volatile int nonfinite_4;
     nonfinite_4 = (float) x <= QNAN;
-    /* { dg-final { scan-tree-dump "nonfinite_4 = \\(float\\)" "original" } } */
+    /* { dg-final { scan-tree-dump "nonfinite_4 = 0" "original" } } */
   }
 
   {
diff --git a/gcc/testsuite/g++.dg/pr88173-1.C b/gcc/testsuite/g++.dg/pr88173-1.C
new file mode 100644
index 00000000000..08fcf97ff16
--- /dev/null
+++ b/gcc/testsuite/g++.dg/pr88173-1.C
@@ -0,0 +1,9 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -std=c++11" } */
+
+#define big __builtin_huge_val()
+#define nan __builtin_nan("")
+
+constexpr bool b1 = big > nan;
+constexpr bool b2 = nan < big;
+
diff --git a/gcc/testsuite/g++.dg/pr88173-2.C b/gcc/testsuite/g++.dg/pr88173-2.C
new file mode 100644
index 00000000000..aa7d7849913
--- /dev/null
+++ b/gcc/testsuite/g++.dg/pr88173-2.C
@@ -0,0 +1,9 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -fsignaling-nans -std=c++11" } */
+
+#define big __builtin_huge_val()
+#define nan __builtin_nan("")
+
+constexpr bool b1 = big > nan;
+constexpr bool b2 = nan < big;
+