Disable unrolling in the loop vectorizer when disabled in the pass manager

When unrolling is disabled in the pass manager, the loop vectorizer should also
not unroll loops. This will allow the -fno-unroll-loops option in Clang to
behave as expected (even for vectorizable loops). The loop vectorizer's
-force-vector-unroll option will (continue to) override the pass-manager
setting (including -force-vector-unroll=0 to force use of the internal
auto-selection logic).

In order to test this, I added a flag to opt (-disable-loop-unrolling) to force
disable unrolling through opt (the analog of -fno-unroll-loops in Clang). Also,
this fixes a small bug in opt where the loop vectorizer was enabled only after
the pass manager populated the queue of passes (the global_alias.ll test needed
a slight update to the RUN line as a result of this fix).

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@189499 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 9 insertions, 3 deletions

diff --git a/tools/opt/opt.cpp b/tools/opt/opt.cpp
index ca82061786..691080aba3 100644
--- a/tools/opt/opt.cpp
+++ b/tools/opt/opt.cpp
@@ -136,6 +136,11 @@ UnitAtATime("funit-at-a-time",
             cl::init(true));
 
 static cl::opt<bool>
+DisableLoopUnrolling("disable-loop-unrolling",
+                     cl::desc("Disable loop unrolling in all relevant passes"),
+                     cl::init(false));
+
+static cl::opt<bool>
 DisableSimplifyLibCalls("disable-simplify-libcalls",
                         cl::desc("Disable simplify-libcalls"));
 
@@ -447,12 +452,13 @@ static void AddOptimizationPasses(PassManagerBase &MPM,FunctionPassManager &FPM,
     Builder.Inliner = createAlwaysInlinerPass();
   }
   Builder.DisableUnitAtATime = !UnitAtATime;
-  Builder.DisableUnrollLoops = OptLevel == 0;
+  Builder.DisableUnrollLoops = (DisableLoopUnrolling.getNumOccurrences() > 0) ?
+                               DisableLoopUnrolling : OptLevel == 0;
   
+  Builder.LoopVectorize = OptLevel > 1 && SizeLevel < 2;
+
   Builder.populateFunctionPassManager(FPM);
   Builder.populateModulePassManager(MPM);
-
-  Builder.LoopVectorize = OptLevel > 1 && SizeLevel < 2;
 }
 
 static void AddStandardCompilePasses(PassManagerBase &PM) {