[BOLT] CMOVConversion pass

Convert simple hammocks into cmov based on misprediction rate.

Test Plan:
- Assembly test: `cmov-conversion.s`
- Testing on a binary:
  # Bootstrap clang with `-x86-cmov-converter-force-all` and `-Wl,--emit-relocs`
  (Release build)
  # Collect perf.data:

    - `clang++ <opts> bolt/lib/Core/BinaryFunction.cpp -E > bf.cpp`
    - `perf record -e cycles:u -j any,u -- clang-15 bf.cpp -O2 -std=c++14 -c -o bf.o`
  # Optimize clang-15 with and w/o -cmov-conversion:
    - `llvm-bolt clang-15 -p perf.data -o clang-15.bolt`
    - `llvm-bolt clang-15 -p perf.data -cmov-conversion -o clang-15.bolt.cmovconv`
  # Run perf experiment:
    - test: `clang-15.bolt.cmovconv`,
    - control: `clang-15.bolt`,
    - workload (clang options): `bf.cpp -O2 -std=c++14 -c -o bf.o`
Results:
```
  task-clock [delta: -360.21 ± 356.75, delta(%): -1.7760 ± 1.7589, p-value: 0.047951, balance: -6]
  instructions  [delta: 44061118 ± 13246382, delta(%): 0.0690 ± 0.0207, p-value: 0.000001, balance: 50]
  icache-misses [delta: -5534468 ± 2779620, delta(%): -0.4331 ± 0.2175, p-value: 0.028014, balance: -28]
  branch-misses [delta: -1624270 ± 1113244, delta(%): -0.3456 ± 0.2368, p-value: 0.030300, balance: -22]
```

Reviewed By: rafauler

Differential Revision: https://reviews.llvm.org/D120177

1 files changed, 9 insertions, 0 deletions

diff --git a/bolt/lib/Rewrite/BinaryPassManager.cpp b/bolt/lib/Rewrite/BinaryPassManager.cpp
index 199ed5f..929b734 100644
--- a/bolt/lib/Rewrite/BinaryPassManager.cpp
+++ b/bolt/lib/Rewrite/BinaryPassManager.cpp
@@ -11,6 +11,7 @@
 #include "bolt/Passes/Aligner.h"
 #include "bolt/Passes/AllocCombiner.h"
 #include "bolt/Passes/AsmDump.h"
+#include "bolt/Passes/CMOVConversion.h"
 #include "bolt/Passes/FrameOptimizer.h"
 #include "bolt/Passes/IdenticalCodeFolding.h"
 #include "bolt/Passes/IndirectCallPromotion.h"
@@ -247,6 +248,11 @@ ThreeWayBranchFlag("three-way-branch",
   cl::desc("reorder three way branches"),
   cl::ZeroOrMore, cl::ReallyHidden, cl::cat(BoltOptCategory));
 
+static cl::opt<bool> CMOVConversionFlag("cmov-conversion",
+                                        cl::desc("fold jcc+mov into cmov"),
+                                        cl::ZeroOrMore, cl::ReallyHidden,
+                                        cl::cat(BoltOptCategory));
+
 } // namespace opts
 
 namespace llvm {
@@ -393,6 +399,9 @@ void BinaryFunctionPassManager::runAllPasses(BinaryContext &BC) {
   Manager.registerPass(std::make_unique<TailDuplication>(),
                        opts::TailDuplicationFlag);
 
+  Manager.registerPass(std::make_unique<CMOVConversion>(),
+                       opts::CMOVConversionFlag);
+
   // This pass syncs local branches with CFG. If any of the following
   // passes breaks the sync - they either need to re-run the pass or
   // fix branches consistency internally.