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[Support] Fix behavior of StringRef::count with overlapping occurrences, add tests

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Summary:
Fix the behavior of StringRef::count(StringRef) to not count overlapping occurrences, as is stated in the documentation.
Fixes bug https://bugs.llvm.org/show_bug.cgi?id=44072

I added Krzysztof Parzyszek to review this change because a use of this function in HexagonInstrInfo::getInlineAsmLength might depend on the overlapping-behavior. I don't have enough domain knowledge to tell if this change could break anything there.

All other uses of this method in LLVM (besides the unit tests) only use single-character search strings. In those cases, search occurrences can not overlap anyway.

Patch by Benno (@Bensge)

Reviewed By: jdoerfert

Differential Revision: https://reviews.llvm.org/D70585
This commit is contained in:
Johannes Doerfert 2019-12-24 17:25:37 -06:00
parent 2d0a36fd96
commit c1d473a27d
2 changed files with 14 additions and 2 deletions
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9
lib/Support/StringRef.cpp
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@ -374,9 +374,14 @@ size_t StringRef::count(StringRef Str) const {
size_t N = Str.size();
if (N > Length)
return 0;
for (size_t i = 0, e = Length - N + 1; i != e; ++i)
if (substr(i, N).equals(Str))
for (size_t i = 0, e = Length - N + 1; i < e;) {
if (substr(i, N).equals(Str)) {
++Count;
i += N;
}
else
++i;
}
return Count;
}

7
unittests/ADT/StringRefTest.cpp
View File

@ -509,6 +509,13 @@ TEST(StringRefTest, Count) {
EXPECT_EQ(1U, Str.count("hello"));
EXPECT_EQ(1U, Str.count("ello"));
EXPECT_EQ(0U, Str.count("zz"));
StringRef OverlappingAbba("abbabba");
EXPECT_EQ(1U, OverlappingAbba.count("abba"));
StringRef NonOverlappingAbba("abbaabba");
EXPECT_EQ(2U, NonOverlappingAbba.count("abba"));
StringRef ComplexAbba("abbabbaxyzabbaxyz");
EXPECT_EQ(2U, ComplexAbba.count("abba"));
}
TEST(StringRefTest, EditDistance) {