llvm-reduce: Skip reducing branches that already have the condition to set

[arsenm]

Summary

This should reduce the number of steps when resuming a
reduction.

[aeubanks]

llvm/tools/llvm-reduce/deltas/ReduceUsingSimplifyCFG.cpp

45

we should prefer either zero or one over the other. if we prefer zero, don't try to to change a zero to a one. we do this in the ReduceOperands pass

[arsenm]

llvm/tools/llvm-reduce/deltas/ReduceUsingSimplifyCFG.cpp

45

The point here isn't to reduce the condition to zero or one. The point is to see what unconditionally branching to one side or the other can do.

[arsenm]

llvm/tools/llvm-reduce/deltas/ReduceUsingSimplifyCFG.cpp

45

Maybe this should proceed and try simplifyCFG anyway, even though that's redundant with the simplify-cfg reduction (which runs later)

[aeubanks]

llvm/tools/llvm-reduce/deltas/ReduceUsingSimplifyCFG.cpp

45

yes, I think that makes sense

[lebedev.ri]

(as per inline comments)

llvm/tools/llvm-reduce/deltas/ReduceUsingSimplifyCFG.cpp

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())
+      if (!BR || !BR->isConditional())
+        continue;
+
+      // Skip cases that already have the value we're going to set this to.
+      ConstantInt *Cond = dyn_cast<ConstantInt>(BR->getCondition());
+      if (Cond) {
+        if (Direction) {
+          if (Cond->isOne())
+            continue;
+        } else {
+          if (Cond->isZero())
+            continue;
+        }
+      }
+
+      if (O.shouldKeep())
         continue;
 
       if (Direction)
         BR->setCondition(ConstantInt::getTrue(BR->getContext()));
       else
         BR->setCondition(ConstantInt::getFalse(BR->getContext()));
 
       ToSimplify.push_back(&BB);