commit 82f983e305acbee44b54cbac45c53709c0cba898
author Eric Christopher <echristo@gmail.com> Mon Oct 14 22:56:07 2019 +0000
committer Eric Christopher <echristo@gmail.com> Mon Oct 14 22:56:07 2019 +0000
tree f7ae0f94a620719ae99f365546afd2cb219ea244
parent dc1d7acad30bf7e81b324a6ed2be36cda50f665b

In the new pass manager use PTO.LoopUnrolling to determine when and how
we will unroll loops. Also comment a few occasions where we need to
know whether or not we're forcing the unwinder or not.

The default before and after this patch is for LoopUnroll to be enabled,
and for it to use a cost model to determine whether to unroll the loop
(`OnlyWhenForced = false`). Before this patch, disabling loop unroll
would not run the LoopUnroll pass. After this patch, the LoopUnroll pass
is being run, but it restricts unrolling to only the loops marked by a
pragma (`OnlyWhenForced = true`).

In addition, this patch disables the UnrollAndJam pass when disabling unrolling.

Testcase is in clang because it's controlling how the loop optimizer
is being set up and there's no other way to trigger the behavior.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@374838 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Passes/PassBuilder.cpp

diff --git a/lib/Passes/PassBuilder.cpp b/lib/Passes/PassBuilder.cpp
index 25558e1..1aaccb5 100644
--- a/lib/Passes/PassBuilder.cpp
+++ b/lib/Passes/PassBuilder.cpp
@@ -471,8 +471,8 @@
   if ((Phase != ThinLTOPhase::PreLink || !PGOOpt ||
        PGOOpt->Action != PGOOptions::SampleUse) &&
       PTO.LoopUnrolling)
-    LPM2.addPass(
-        LoopFullUnrollPass(Level, false, PTO.ForgetAllSCEVInLoopUnroll));
+    LPM2.addPass(LoopFullUnrollPass(Level, /*OnlyWhenForced=*/false,
+                                    PTO.ForgetAllSCEVInLoopUnroll));
 
   for (auto &C : LoopOptimizerEndEPCallbacks)
     C(LPM2, Level);
@@ -953,13 +953,13 @@
   // combiner for cleanup here so that the unrolling and LICM can be pipelined
   // across the loop nests.
   // We do UnrollAndJam in a separate LPM to ensure it happens before unroll
-  if (EnableUnrollAndJam) {
+  if (EnableUnrollAndJam && PTO.LoopUnrolling) {
     OptimizePM.addPass(
         createFunctionToLoopPassAdaptor(LoopUnrollAndJamPass(Level)));
   }
-  if (PTO.LoopUnrolling)
-    OptimizePM.addPass(LoopUnrollPass(
-        LoopUnrollOptions(Level, false, PTO.ForgetAllSCEVInLoopUnroll)));
+  OptimizePM.addPass(LoopUnrollPass(
+      LoopUnrollOptions(Level, /*OnlyWhenForced=*/!PTO.LoopUnrolling,
+                        PTO.ForgetAllSCEVInLoopUnroll)));
   OptimizePM.addPass(WarnMissedTransformationsPass());
   OptimizePM.addPass(InstCombinePass());
   OptimizePM.addPass(RequireAnalysisPass<OptimizationRemarkEmitterAnalysis, Function>());