1 files changed, 18 insertions, 7 deletions

diff --git a/llvm/lib/Transforms/IPO/PassManagerBuilder.cpp b/llvm/lib/Transforms/IPO/PassManagerBuilder.cpp
index 9e241aa335a..7491fe06841 100644
--- a/llvm/lib/Transforms/IPO/PassManagerBuilder.cpp
+++ b/llvm/lib/Transforms/IPO/PassManagerBuilder.cpp
@@ -158,6 +158,12 @@ cl::opt<bool> EnableOrderFileInstrumentation(
     "enable-order-file-instrumentation", cl::init(false), cl::Hidden,
     cl::desc("Enable order file instrumentation (default = off)"));
 
+cl::opt<bool> ForgetSCEVInLoopUnroll(
+    "forget-scev-loop-unroll", cl::init(false), cl::Hidden,
+    cl::desc("Forget everything in SCEV when doing LoopUnroll, instead of just"
+             " the current top-most loop. This is somtimes preferred to reduce"
+             " compile time."));
+
 PassManagerBuilder::PassManagerBuilder() {
     OptLevel = 2;
     SizeLevel = 0;
@@ -169,6 +175,7 @@ PassManagerBuilder::PassManagerBuilder() {
     RerollLoops = RunLoopRerolling;
     NewGVN = RunNewGVN;
     DisableGVNLoadPRE = false;
+    ForgetAllSCEVInLoopUnroll = ForgetSCEVInLoopUnroll;
     VerifyInput = false;
     VerifyOutput = false;
     MergeFunctions = false;
@@ -386,8 +393,9 @@ void PassManagerBuilder::addFunctionSimplificationPasses(
   if (EnableLoopInterchange)
     MPM.add(createLoopInterchangePass()); // Interchange loops
 
-  MPM.add(createSimpleLoopUnrollPass(OptLevel,
-                                     DisableUnrollLoops)); // Unroll small loops
+  // Unroll small loops
+  MPM.add(createSimpleLoopUnrollPass(OptLevel, DisableUnrollLoops,
+                                     ForgetAllSCEVInLoopUnroll));
   addExtensionsToPM(EP_LoopOptimizerEnd, MPM);
   // This ends the loop pass pipelines.
 
@@ -724,8 +732,9 @@ void PassManagerBuilder::populateModulePassManager(
     MPM.add(createLoopUnrollAndJamPass(OptLevel));
   }
 
-  MPM.add(createLoopUnrollPass(OptLevel,
-                               DisableUnrollLoops)); // Unroll small loops
+  // Unroll small loops
+  MPM.add(createLoopUnrollPass(OptLevel, DisableUnrollLoops,
+                               ForgetAllSCEVInLoopUnroll));
 
   if (!DisableUnrollLoops) {
     // LoopUnroll may generate some redundency to cleanup.
@@ -919,11 +928,13 @@ void PassManagerBuilder::addLTOOptimizationPasses(legacy::PassManagerBase &PM) {
   if (EnableLoopInterchange)
     PM.add(createLoopInterchangePass());
 
-  PM.add(createSimpleLoopUnrollPass(OptLevel,
-                                    DisableUnrollLoops)); // Unroll small loops
+  // Unroll small loops
+  PM.add(createSimpleLoopUnrollPass(OptLevel, DisableUnrollLoops,
+                                    ForgetAllSCEVInLoopUnroll));
   PM.add(createLoopVectorizePass(true, !LoopVectorize));
   // The vectorizer may have significantly shortened a loop body; unroll again.
-  PM.add(createLoopUnrollPass(OptLevel, DisableUnrollLoops));
+  PM.add(createLoopUnrollPass(OptLevel, DisableUnrollLoops,
+                              ForgetAllSCEVInLoopUnroll));
 
   PM.add(createWarnMissedTransformationsPass());