[llvm] 17f7654 - [NFCI][MachineCopyPropagation] invalidateRegister(): use SmallSet<8> instead of DenseSet.

[Roman Lebedev via llvm-commits]

Author: Roman Lebedev
Date: 2020-06-12T23:10:54+03:00
New Revision: 17f765415245dc59bdf17d8e2b6911cba3aeb504

URL: https://github.com/llvm/llvm-project/commit/17f765415245dc59bdf17d8e2b6911cba3aeb504
DIFF: https://github.com/llvm/llvm-project/commit/17f765415245dc59bdf17d8e2b6911cba3aeb504.diff

LOG: [NFCI][MachineCopyPropagation] invalidateRegister(): use SmallSet<8> instead of DenseSet.

This decreases the time consumed by the pass [during RawSpeed unity build]
by 25% (0.0586 s -> 0.04388 s).

While that isn't really impressive overall, that wasn't the goal here.
The memory results here are noticeable.
The baseline results are:
```
total runtime: 55.65s.
calls to allocation functions: 19754254 (354960/s)
temporary memory allocations: 4951609 (88974/s)
peak heap memory consumption: 239.13MB
peak RSS (including heaptrack overhead): 463.79MB
total memory leaked: 198.01MB
```
While with this patch the results are:
```
total runtime: 55.37s.
calls to allocation functions: 19068237 (344403/s)   # -3.47 %
temporary memory allocations: 4261772 (76974/s)      # -13.93 % (!!!)
peak heap memory consumption: 239.13MB
peak RSS (including heaptrack overhead): 463.73MB
total memory leaked: 198.01MB
```

So we get rid of *a lot* of temporary allocations.

Using `SmallSet<8>` makes sense to me because at least here
for x86 BdVer2, the size of that set is *never* more than 3,
over all of llvm test-suite + RawSpeed.

The story might be different on other targets,
not sure if it will ever justify whole DenseSet,
but if it does SmallDenseSet might be a compromise.

Added: 
    

Modified: 
    llvm/lib/CodeGen/MachineCopyPropagation.cpp

Removed: 
    


################################################################################
diff  --git a/llvm/lib/CodeGen/MachineCopyPropagation.cpp b/llvm/lib/CodeGen/MachineCopyPropagation.cpp
index c316b167059b..70d6dcc2e3e2 100644
--- a/llvm/lib/CodeGen/MachineCopyPropagation.cpp
+++ b/llvm/lib/CodeGen/MachineCopyPropagation.cpp
@@ -51,6 +51,7 @@
 #include "llvm/ADT/DenseMap.h"
 #include "llvm/ADT/STLExtras.h"
 #include "llvm/ADT/SetVector.h"
+#include "llvm/ADT/SmallSet.h"
 #include "llvm/ADT/SmallVector.h"
 #include "llvm/ADT/Statistic.h"
 #include "llvm/ADT/iterator_range.h"
@@ -113,7 +114,8 @@ class CopyTracker {
     // Since Reg might be a subreg of some registers, only invalidate Reg is not
     // enough. We have to find the COPY defines Reg or registers defined by Reg
     // and invalidate all of them.
-    DenseSet<unsigned> RegsToInvalidate{Reg};
+    SmallSet<unsigned, 8> RegsToInvalidate;
+    RegsToInvalidate.insert(Reg);
     for (MCRegUnitIterator RUI(Reg, &TRI); RUI.isValid(); ++RUI) {
       auto I = Copies.find(*RUI);
       if (I != Copies.end()) {