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authorGravatar Benjamin Barenblat <bbaren@google.com>2021-03-04 14:43:19 -0500
committerGravatar Benjamin Barenblat <bbaren@google.com>2021-03-04 14:43:19 -0500
commit006b28a982e3938d29952341a2ebdeae77b42b16 (patch)
tree81af5070e7a04c579354e90d7c9e1668f8af0762 /debian/patches
parent7879e9278a48b4bf7727b640ea1485bf3fb01eb8 (diff)
Make Abseil unit tests tolerate fused multiply/add contraction
Apply a patch from upstream to make tests pass when GCC replaces double addition and multiplication with fused multiply/add instructions.
Diffstat (limited to 'debian/patches')
-rw-r--r--debian/patches/fma-contraction.diff63
-rw-r--r--debian/patches/series1
2 files changed, 64 insertions, 0 deletions
diff --git a/debian/patches/fma-contraction.diff b/debian/patches/fma-contraction.diff
new file mode 100644
index 00000000..95181a36
--- /dev/null
+++ b/debian/patches/fma-contraction.diff
@@ -0,0 +1,63 @@
+From: Benjamin Barenblat <bbaren@google.com>
+Subject: Make tests tolerant of FMA contraction
+Forwarded: yes
+Applied-Upstream: https://github.com/abseil/abseil-cpp/commit/b0735979d778a768caee207f01f327535cbd2140
+
+Weaken Duration.ToDoubleSecondsCheckEdgeCases and
+Duration.ToDoubleSecondsCheckRandom to make them less sensitive to fused
+multiply/add contraction.
+
+The author works at Google. Upstream applied this patch as Piper
+revision 360297653 and exported it to GitHub; the the Applied-Upstream URL
+above points to the exported commit.
+
+--- a/absl/time/duration_test.cc
++++ b/absl/time/duration_test.cc
+@@ -1369,10 +1369,13 @@
+ EXPECT_THAT(ToTimeval(absl::Nanoseconds(2000)), TimevalMatcher(tv));
+ }
+
+-void VerifySameAsMul(double time_as_seconds, int* const misses) {
++void VerifyApproxSameAsMul(double time_as_seconds, int* const misses) {
+ auto direct_seconds = absl::Seconds(time_as_seconds);
+ auto mul_by_one_second = time_as_seconds * absl::Seconds(1);
+- if (direct_seconds != mul_by_one_second) {
++ // These are expected to differ by up to one tick due to fused multiply/add
++ // contraction.
++ if (absl::AbsDuration(direct_seconds - mul_by_one_second) >
++ absl::time_internal::MakeDuration(0, 1u)) {
+ if (*misses > 10) return;
+ ASSERT_LE(++(*misses), 10) << "Too many errors, not reporting more.";
+ EXPECT_EQ(direct_seconds, mul_by_one_second)
+@@ -1384,7 +1387,8 @@
+ // For a variety of interesting durations, we find the exact point
+ // where one double converts to that duration, and the very next double
+ // converts to the next duration. For both of those points, verify that
+-// Seconds(point) returns the same duration as point * Seconds(1.0)
++// Seconds(point) returns a duration near point * Seconds(1.0). (They may
++// not be exactly equal due to fused multiply/add contraction.)
+ TEST(Duration, ToDoubleSecondsCheckEdgeCases) {
+ constexpr uint32_t kTicksPerSecond = absl::time_internal::kTicksPerSecond;
+ constexpr auto duration_tick = absl::time_internal::MakeDuration(0, 1u);
+@@ -1423,8 +1427,8 @@
+ }
+ // Now low_edge is the highest double that converts to Duration d,
+ // and high_edge is the lowest double that converts to Duration after_d.
+- VerifySameAsMul(low_edge, &misses);
+- VerifySameAsMul(high_edge, &misses);
++ VerifyApproxSameAsMul(low_edge, &misses);
++ VerifyApproxSameAsMul(high_edge, &misses);
+ }
+ }
+ }
+@@ -1444,8 +1448,8 @@
+ int misses = 0;
+ for (int i = 0; i < 1000000; ++i) {
+ double d = std::exp(uniform(gen));
+- VerifySameAsMul(d, &misses);
+- VerifySameAsMul(-d, &misses);
++ VerifyApproxSameAsMul(d, &misses);
++ VerifyApproxSameAsMul(-d, &misses);
+ }
+ }
+
diff --git a/debian/patches/series b/debian/patches/series
index ceceb694..c07c5a22 100644
--- a/debian/patches/series
+++ b/debian/patches/series
@@ -7,3 +7,4 @@ nan-narrowing.diff
endian-hash.diff
endian-random.diff
ppc-float-conversion.diff
+fma-contraction.diff