llvm-reduce: Add conditional reduction passes

Copy this technique from bugpoint. Before trying to blindly
delete blocks, try to fold branch conditions. This intuitively
makes more sense for a faster reduction, since you can find
dead paths in the function to prune out before trying to bisect
blocks in source order.

Seems to provide some speedup on my multi-hour reduction samples.

This does have the potential to produce testcases with unreachable
blocks. This is already a problem with the existing block
reduction pass. I'm struggling dealing with invalid reductions
in these cases, so in the future this should probably start
deleting those. However, I do sometimes try to reduce failures
in code that becomes unreachable, so I'm not totally sure
what to do here.

3 files changed, 40 insertions, 0 deletions

diff --git a/llvm/tools/llvm-reduce/DeltaManager.cpp b/llvm/tools/llvm-reduce/DeltaManager.cpp
index 048a83c..ee29b44 100644
--- a/llvm/tools/llvm-reduce/DeltaManager.cpp
+++ b/llvm/tools/llvm-reduce/DeltaManager.cpp
@@ -74,6 +74,8 @@ static cl::list<std::string>
     DELTA_PASS("function-bodies", reduceFunctionBodiesDeltaPass)               \
     DELTA_PASS("special-globals", reduceSpecialGlobalsDeltaPass)               \
     DELTA_PASS("aliases", reduceAliasesDeltaPass)                              \
+    DELTA_PASS("simplify-conditionals-true", reduceConditionalsTrueDeltaPass)  \
+    DELTA_PASS("simplify-conditionals-false", reduceConditionalsFalseDeltaPass)\
     DELTA_PASS("basic-blocks", reduceBasicBlocksDeltaPass)                     \
     DELTA_PASS("global-values", reduceGlobalValuesDeltaPass)                   \
     DELTA_PASS("global-objects", reduceGlobalObjectsDeltaPass)                 \
diff --git a/llvm/tools/llvm-reduce/deltas/ReduceUsingSimplifyCFG.cpp b/llvm/tools/llvm-reduce/deltas/ReduceUsingSimplifyCFG.cpp
index a45d571..416b165 100644
--- a/llvm/tools/llvm-reduce/deltas/ReduceUsingSimplifyCFG.cpp
+++ b/llvm/tools/llvm-reduce/deltas/ReduceUsingSimplifyCFG.cpp
@@ -13,6 +13,8 @@
 
 #include "ReduceUsingSimplifyCFG.h"
 #include "llvm/Analysis/TargetTransformInfo.h"
+#include "llvm/IR/Constants.h"
+#include "llvm/IR/Instructions.h"
 #include "llvm/Transforms/Utils/Local.h"
 
 using namespace llvm;
@@ -31,3 +33,37 @@ static void reduceUsingSimplifyCFG(Oracle &O, Module &Program) {
 void llvm::reduceUsingSimplifyCFGDeltaPass(TestRunner &Test) {
   runDeltaPass(Test, reduceUsingSimplifyCFG, "Reducing using SimplifyCFG");
 }
+static void reduceConditionals(Oracle &O, Module &M, bool Direction) {
+  SmallVector<BasicBlock *, 16> ToSimplify;
+
+  for (auto &F : M) {
+    for (auto &BB : F) {
+      auto *BR = dyn_cast<BranchInst>(BB.getTerminator());
+      if (!BR || !BR->isConditional() || O.shouldKeep())
+        continue;
+
+      if (Direction)
+        BR->setCondition(ConstantInt::getTrue(BR->getContext()));
+      else
+        BR->setCondition(ConstantInt::getFalse(BR->getContext()));
+
+      ToSimplify.push_back(&BB);
+    }
+  }
+
+  TargetTransformInfo TTI(M.getDataLayout());
+  for (auto *BB : ToSimplify)
+    simplifyCFG(BB, TTI);
+}
+
+void llvm::reduceConditionalsTrueDeltaPass(TestRunner &Test) {
+  runDeltaPass(
+      Test, [](Oracle &O, Module &M) { reduceConditionals(O, M, true); },
+      "Reducing conditional branches to true");
+}
+
+void llvm::reduceConditionalsFalseDeltaPass(TestRunner &Test) {
+  runDeltaPass(
+      Test, [](Oracle &O, Module &M) { reduceConditionals(O, M, false); },
+      "Reducing conditional branches to false");
+}
diff --git a/llvm/tools/llvm-reduce/deltas/ReduceUsingSimplifyCFG.h b/llvm/tools/llvm-reduce/deltas/ReduceUsingSimplifyCFG.h
index 56cd15a..01a1460 100644
--- a/llvm/tools/llvm-reduce/deltas/ReduceUsingSimplifyCFG.h
+++ b/llvm/tools/llvm-reduce/deltas/ReduceUsingSimplifyCFG.h
@@ -18,6 +18,8 @@
 
 namespace llvm {
 void reduceUsingSimplifyCFGDeltaPass(TestRunner &Test);
+void reduceConditionalsTrueDeltaPass(TestRunner &Test);
+void reduceConditionalsFalseDeltaPass(TestRunner &Test);
 } // namespace llvm
 
 #endif