[IR] Switch AttributeList to use an array for O(1) access
Summary:
Before this change, AttributeLists stored a pair of index and
AttributeSet. This is memory efficient if most arguments do not have
attributes. However, it requires doing a search over the pairs to test
an argument or function attribute. Profiling shows that this loop was
0.76% of the time in 'opt -O2' of sqlite3.c, because LLVM constantly
tests values for nullability.
This was worth about 2.5% of mid-level optimization cycles on the
sqlite3 amalgamation. Here are the full perf results:
https://reviews.llvm.org/P7995
Here are just the before and after cycle counts:
```
$ perf stat -r 5 ./opt_before -O2 sqlite3.bc -o /dev/null
13,274,181,184 cycles # 3.047 GHz ( +- 0.28% )
$ perf stat -r 5 ./opt_after -O2 sqlite3.bc -o /dev/null
12,906,927,263 cycles # 3.043 GHz ( +- 0.51% )
```
This patch *does not* change the indices used to query attributes, as
requested by reviewers. Tracking whether an index is usable for array
indexing is a huge pain that affects many of the internal APIs, so it
would be good to come back later and do a cleanup to remove this
internal adjustment.
Reviewers: pete, chandlerc
Subscribers: javed.absar, llvm-commits
Differential Revision: https://reviews.llvm.org/D32819
llvm-svn: 303654
diff --git a/llvm/lib/Transforms/Utils/FunctionComparator.cpp b/llvm/lib/Transforms/Utils/FunctionComparator.cpp
index 73a0b27..57468be 100644
--- a/llvm/lib/Transforms/Utils/FunctionComparator.cpp
+++ b/llvm/lib/Transforms/Utils/FunctionComparator.cpp
@@ -76,12 +76,14 @@
int FunctionComparator::cmpAttrs(const AttributeList L,
const AttributeList R) const {
- if (int Res = cmpNumbers(L.getNumSlots(), R.getNumSlots()))
+ if (int Res = cmpNumbers(L.getNumAttrSets(), R.getNumAttrSets()))
return Res;
- for (unsigned i = 0, e = L.getNumSlots(); i != e; ++i) {
- AttributeList::iterator LI = L.begin(i), LE = L.end(i), RI = R.begin(i),
- RE = R.end(i);
+ for (unsigned i = L.index_begin(), e = L.index_end(); i != e; ++i) {
+ AttributeSet LAS = L.getAttributes(i);
+ AttributeSet RAS = R.getAttributes(i);
+ AttributeSet::iterator LI = LAS.begin(), LE = LAS.end();
+ AttributeSet::iterator RI = RAS.begin(), RE = RAS.end();
for (; LI != LE && RI != RE; ++LI, ++RI) {
Attribute LA = *LI;
Attribute RA = *RI;