Don't pass null to memcmp.

This will allow us to add nonnull-attribute to the UBSAN bot.

We are in fact hitting a case where one of the arguments is null and the other
not, which seems dicey.  I think the scenario is comparing the empty pathref
with another path ref that's just been COWed, without any verbs or points yet.

BUG=skia:

Review URL: https://codereview.chromium.org/732643002

2 files changed, 11 insertions, 1 deletions

diff --git a/src/core/SkPathRef.cpp b/src/core/SkPathRef.cpp
index dffb6a3646..ad85fd06a8 100644
--- a/src/core/SkPathRef.cpp
+++ b/src/core/SkPathRef.cpp
@@ -193,12 +193,18 @@ bool SkPathRef::operator== (const SkPathRef& ref) const {
         SkASSERT(!genIDMatch);
         return false;
     }
+    if (0 == ref.fVerbCnt) {
+        SkASSERT(0 == ref.fPointCnt);
+        return true;
+    }
+    SkASSERT(this->verbsMemBegin() && ref.verbsMemBegin());
     if (0 != memcmp(this->verbsMemBegin(),
                     ref.verbsMemBegin(),
                     ref.fVerbCnt * sizeof(uint8_t))) {
         SkASSERT(!genIDMatch);
         return false;
     }
+    SkASSERT(this->points() && ref.points());
     if (0 != memcmp(this->points(),
                     ref.points(),
                     ref.fPointCnt * sizeof(SkPoint))) {
diff --git a/tests/PathTest.cpp b/tests/PathTest.cpp
index bc3a3d7bdb..94b91d261b 100644
--- a/tests/PathTest.cpp
+++ b/tests/PathTest.cpp
@@ -3435,7 +3435,11 @@ static void compare_dump(skiatest::Reporter* reporter, const SkPath& path, bool
     path.dump(&wStream, force, dumpAsHex);
     SkAutoDataUnref data(wStream.copyToData());
     REPORTER_ASSERT(reporter, data->size() == strlen(str));
-    REPORTER_ASSERT(reporter, !memcmp(data->data(), str, strlen(str)));
+    if (strlen(str) > 0) {
+        REPORTER_ASSERT(reporter, !memcmp(data->data(), str, strlen(str)));
+    } else {
+        REPORTER_ASSERT(reporter, data->data() == NULL || !memcmp(data->data(), str, strlen(str)));
+    }
 }
 
 static void test_dump(skiatest::Reporter* reporter) {