[pass-manager] Add an option -sil-disable-skipping-passes that ensures that the bottom up pass manager never skips functions.

This ensures that when one is bisecting on pass counts, regardless of whether or
not one removes code in the test case, the pass counts being run remain the
same.

Author: gottesmm

lib/SILOptimizer/PassManager/PassManager.cpp

@@ -95,6 +95,9 @@ llvm::cl::opt<bool> SILVerifyWithoutInvalidation(
     "sil-verify-without-invalidation", llvm::cl::init(false),
     llvm::cl::desc("Verify after passes even if the pass has not invalidated"));
 
+llvm::cl::opt<bool> SILDisableSkippingPasses(
+    "sil-disable-skipping-passes", llvm::cl::init(false),
+    llvm::cl::desc("Do not skip passes even if nothing was changed"));
 
 static llvm::ManagedStatic<std::vector<unsigned>> DebugPassNumbers;
 
@@ -290,7 +293,8 @@ void SILPassManager::runPassesOnFunction(PassList FuncTransforms,
 
     // If nothing changed since the last run of this pass, we can skip this
     // pass.
-    if (completedPasses.test((size_t)SFT->getPassKind())) {
+    if (completedPasses.test((size_t)SFT->getPassKind()) &&
+        !SILDisableSkippingPasses) {
       if (SILPrintPassName)
         llvm::dbgs() << "(Skip) Stage: " << StageName
                      << " Pass: " << SFT->getName()