[ARM] ParallelDSP: add option to disable the pass

[SjoerdMeijer]

Summary

Seems useful for debugging purposes.

[dmgreen]

This looks like a sensible idea.

The pass will also need "new pass manager" code at some point.

[dmgreen]

In D50511#1196431, @dmgreen wrote:

The pass will also need "new pass manager" code at some point.

Actually, that might not be true for how late in the pipeline this runs. I'm surprised how late this is, I'd expected it a little earlier.

[SjoerdMeijer]

Thanks for reviewing.

I'm surprised how late this is, I'd expected it a little earlier.

Main motivation to run it very late is that it is ARM specific, and we didn't want to interfere with other optimisations. Other than that, no good reason, and we could reconsider of course.

llvm/trunk/lib/Target/ARM/ARMParallelDSP.cpp

 
 using namespace llvm;
 using namespace PatternMatch;
 
 #define DEBUG_TYPE "arm-parallel-dsp"
 
 STATISTIC(NumSMLAD , "Number of smlad instructions generated");
 
+static cl::opt<bool>
+DisableParallelDSP("disable-arm-parallel-dsp", cl::Hidden, cl::init(false),
+                   cl::desc("Disable the ARM Parallel DSP pass"));
+
 namespace {
   struct OpChain;
   struct BinOpChain;
   struct Reduction;
 
   using OpChainList     = SmallVector<std::unique_ptr<OpChain>, 8>;
   using ReductionList   = SmallVector<Reduction, 8>;
   using ValueList       = SmallVector<Value*, 8>;
void getAnalysisUsage(AnalysisUsage &AU) const override {
       AU.addRequired<LoopInfoWrapperPass>();
       AU.addRequired<DominatorTreeWrapperPass>();
       AU.addRequired<TargetPassConfig>();
       AU.addPreserved<LoopInfoWrapperPass>();
       AU.setPreservesCFG();
     }
 
     bool runOnLoop(Loop *TheLoop, LPPassManager &) override {
+      if (DisableParallelDSP)
+        return false;
       L = TheLoop;
       SE = &getAnalysis<ScalarEvolutionWrapperPass>().getSE();
       AA = &getAnalysis<AAResultsWrapperPass>().getAAResults();
       TLI = &getAnalysis<TargetLibraryInfoWrapperPass>().getTLI();
       DT = &getAnalysis<DominatorTreeWrapperPass>().getDomTree();
       LI = &getAnalysis<LoopInfoWrapperPass>().getLoopInfo();
       auto &TPC = getAnalysis<TargetPassConfig>();