[Polly][ScopBuilder] Make -polly-stmt-granularity=scalar-indep the default.

[Meinersbur]

Summary

Splitting basic blocks into multiple statements if there are now additional scalar dependencies gives more freedom to the scheduler, but more statements also means higher compile-time complexity. Switch to finer statement granularity, the additional compile time should be limited by the number of operations quota.

[grosser]

LGTM

[Meinersbur]

Instead of adding -polly-stmt-granulairy=bb globally, only add the flag to the tests that need it.

This avoids additional discrepancy between Polly's default settings and neew regression tests.

Many differences stem from statements for cmp instructions being created, but then simplified-away because such statments contain no write.

[Meinersbur]

Waiting for confirmation this is ok before committing

[grosser]

LGTM.

lib/Analysis/ScopBuilder.cpp

static cl::opt<GranularityChoice> StmtGranularity(
     cl::desc(
         "Algorithm to use for splitting basic blocks into multiple statements"),
     cl::values(clEnumValN(GranularityChoice::BasicBlocks, "bb",
                           "One statement per basic block"),
                clEnumValN(GranularityChoice::ScalarIndependence, "scalar-indep",
                           "Scalar independence heuristic"),
                clEnumValN(GranularityChoice::Stores, "store",
                           "Store-level granularity")),
-    cl::init(GranularityChoice::BasicBlocks), cl::cat(PollyCategory));
+    cl::init(GranularityChoice::ScalarIndependence), cl::cat(PollyCategory),
+    cl::ZeroOrMore);
 
 void ScopBuilder::buildPHIAccesses(ScopStmt *PHIStmt, PHINode *PHI,
                                    Region *NonAffineSubRegion,
                                    bool IsExitBlock) {
   // PHI nodes that are in the exit block of the region, hence if IsExitBlock is
   // true, are not modeled as ordinary PHI nodes as they are not part of the
   // region. However, we model the operands in the predecessor blocks that are
   // part of the region as regular scalar accesses.

test/lit.site.cfg.in

config.substitutions.append(('%loadPolly', '-load '
                                  ))
 else:
     config.substitutions.append(('%loadPolly', ''
                                  + ' -polly-process-unprofitable '
                                  + ' -polly-remarks-minimal '
                                  + ' -polly-use-llvm-names '
                                  + ' -polly-import-jscop-dir=%S '
                                  + ' -polly-codegen-verify '
+                                 + ' -polly-stmt-granularity=bb '
                                  ))
 
 if config.enable_gpgpu_codegen == 'TRUE' :
     config.available_features.add('pollyacc')
 
 # Let the main config do the real work.
 lit_config.load_config(config, "@POLLY_SOURCE_DIR@/test/lit.cfg")