[builtins] Divide shouldn't underflow if rounded result would be normal.

We were treating certain edge cases that are actually normal as denormal
results, and flushing them to zero; we shouldn't do that. Not sure this
is the cleanest way to implement this edge case, but I wanted to avoid
adding any code on the common path.

Differential Revision: https://reviews.llvm.org/D59070

llvm-svn: 356529

1 files changed, 45 insertions, 0 deletions

diff --git a/compiler-rt/test/builtins/Unit/divdf3_test.c b/compiler-rt/test/builtins/Unit/divdf3_test.c
new file mode 100644
index 00000000000..00b021f4ec7
--- /dev/null
+++ b/compiler-rt/test/builtins/Unit/divdf3_test.c
@@ -0,0 +1,45 @@
+// RUN: %clang_builtins %s %librt -o %t && %run %t
+//===--------------- divdf3_test.c - Test __divdf3 ------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+//
+// This file tests __divdf3 for the compiler_rt library.
+//
+//===----------------------------------------------------------------------===//
+
+#include "int_lib.h"
+#include <stdio.h>
+
+#include "fp_test.h"
+
+// Returns: a / b
+COMPILER_RT_ABI double __divdf3(double a, double b);
+
+int test__divdf3(double a, double b, uint64_t expected)
+{
+    double x = __divdf3(a, b);
+    int ret = compareResultD(x, expected);
+
+    if (ret){
+        printf("error in test__divdf3(%.20e, %.20e) = %.20e, "
+               "expected %.20e\n", a, b, x,
+               fromRep64(expected));
+    }
+    return ret;
+}
+
+int main()
+{
+    // 1/3
+    if (test__divdf3(1., 3., 0x3fd5555555555555ULL))
+      return 1;
+    // smallest normal result
+    if (test__divdf3(4.450147717014403e-308, 2., 0x10000000000000ULL))
+      return 1;
+
+    return 0;
+}