[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

1 files changed, 6 insertions, 0 deletions

diff --git a/llvm/lib/IR/Instructions.cpp b/llvm/lib/IR/Instructions.cpp
index 01d4ed6c8ee..00ac2037f1f 100644
--- a/llvm/lib/IR/Instructions.cpp
+++ b/llvm/lib/IR/Instructions.cpp
@@ -454,6 +454,9 @@ bool CallInst::dataOperandHasImpliedAttr(unsigned i,
   // question is a call argument; or be indirectly implied by the kind of its
   // containing operand bundle, if the operand is a bundle operand.
 
+  if (i == Attribute::ReturnIndex)
+    return hasRetAttr(Kind);
+
   // FIXME: Avoid these i - 1 calculations and update the API to use zero-based
   // indices.
   if (i < (getNumArgOperands() + 1))
@@ -779,6 +782,9 @@ bool InvokeInst::dataOperandHasImpliedAttr(unsigned i,
   // question is an invoke argument; or be indirectly implied by the kind of its
   // containing operand bundle, if the operand is a bundle operand.
 
+  if (i == Attribute::ReturnIndex)
+    return hasRetAttr(Kind);
+
   // FIXME: Avoid these i - 1 calculations and update the API to use zero-based
   // indices.
   if (i < (getNumArgOperands() + 1))