[llvm] r347464 - [llvm-mca] Use a SmallVector instead of std::vector to track register reads/writes. NFCI

[Andrea Di Biagio via llvm-commits]

Author: adibiagio
Date: Thu Nov 22 06:48:53 2018
New Revision: 347464

URL: http://llvm.org/viewvc/llvm-project?rev=347464&view=rev
Log:
[llvm-mca] Use a SmallVector instead of std::vector to track register reads/writes. NFCI

This avoids a heap allocation most of the times.
This patch gives a small but consistent 3% speedup on a release build (up to ~5%
on a debug build).

Modified:
    llvm/trunk/tools/llvm-mca/include/Instruction.h
    llvm/trunk/tools/llvm-mca/lib/Instruction.cpp

Modified: llvm/trunk/tools/llvm-mca/include/Instruction.h
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/tools/llvm-mca/include/Instruction.h?rev=347464&r1=347463&r2=347464&view=diff
==============================================================================
--- llvm/trunk/tools/llvm-mca/include/Instruction.h (original)
+++ llvm/trunk/tools/llvm-mca/include/Instruction.h Thu Nov 22 06:48:53 2018
@@ -26,8 +26,6 @@
 #endif
 
 #include <memory>
-#include <set>
-#include <vector>
 
 namespace llvm {
 namespace mca {
@@ -134,7 +132,7 @@ class WriteState {
   // gets notified with the actual CyclesLeft.
 
   // The 'second' element of a pair is a "ReadAdvance" number of cycles.
-  std::set<std::pair<ReadState *, int>> Users;
+  SmallVector<std::pair<ReadState *, int>, 4> Users;
 
 public:
   WriteState(const WriteDescriptor &Desc, unsigned RegID,
@@ -319,15 +317,16 @@ struct ResourceUsage {
 
 /// An instruction descriptor
 struct InstrDesc {
-  std::vector<WriteDescriptor> Writes; // Implicit writes are at the end.
-  std::vector<ReadDescriptor> Reads;   // Implicit reads are at the end.
+  SmallVector<WriteDescriptor, 4> Writes; // Implicit writes are at the end.
+  SmallVector<ReadDescriptor, 4> Reads;   // Implicit reads are at the end.
 
   // For every resource used by an instruction of this kind, this vector
   // reports the number of "consumed cycles".
-  std::vector<std::pair<uint64_t, ResourceUsage>> Resources;
+  SmallVector<std::pair<uint64_t, ResourceUsage>, 4> Resources;
 
   // A list of buffered resources consumed by this instruction.
-  std::vector<uint64_t> Buffers;
+  SmallVector<uint64_t, 4> Buffers;
+
   unsigned MaxLatency;
   // Number of MicroOps for this instruction.
   unsigned NumMicroOps;

Modified: llvm/trunk/tools/llvm-mca/lib/Instruction.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/tools/llvm-mca/lib/Instruction.cpp?rev=347464&r1=347463&r2=347464&view=diff
==============================================================================
--- llvm/trunk/tools/llvm-mca/lib/Instruction.cpp (original)
+++ llvm/trunk/tools/llvm-mca/lib/Instruction.cpp Thu Nov 22 06:48:53 2018
@@ -65,8 +65,11 @@ void WriteState::addUser(ReadState *User
     return;
   }
 
-  std::pair<ReadState *, int> NewPair(User, ReadAdvance);
-  Users.insert(NewPair);
+  if (llvm::find_if(Users, [&User](const std::pair<ReadState *, int> &Use) {
+        return Use.first == User;
+      }) == Users.end()) {
+    Users.emplace_back(User, ReadAdvance);
+  }
 }
 
 void WriteState::addUser(WriteState *User) {