[LoopReroll] Fix reroll root legality checking.

The code checked that the first root was an appropriate distance from
the base value, but skipped checking the other roots. This could lead to
rerolling a loop that can't be legally rerolled (at least, not without
rewriting the loop in a non-trivial way).

Differential Revision: https://reviews.llvm.org/D56812

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@353779 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/lib/Transforms/Scalar/LoopRerollPass.cpp b/lib/Transforms/Scalar/LoopRerollPass.cpp
index 17aa442d86e9bc6a932ff36587f3cdaae3cde970..166b57f20b43fadb7a59c01e824dece53b2a37cb 100644 (file)
--- a/lib/Transforms/Scalar/LoopRerollPass.cpp
+++ b/lib/Transforms/Scalar/LoopRerollPass.cpp
@@ -891,12 +891,22 @@ bool LoopReroll::DAGRootTracker::validateRootSet(DAGRootSet &DRS) {
   const auto *ADR = dyn_cast<SCEVAddRecExpr>(SE->getSCEV(DRS.BaseInst));
   if (!ADR)
     return false;
+
+  // Check that the first root is evenly spaced.
   unsigned N = DRS.Roots.size() + 1;
   const SCEV *StepSCEV = SE->getMinusSCEV(SE->getSCEV(DRS.Roots[0]), ADR);
   const SCEV *ScaleSCEV = SE->getConstant(StepSCEV->getType(), N);
   if (ADR->getStepRecurrence(*SE) != SE->getMulExpr(StepSCEV, ScaleSCEV))
     return false;
 
+  // Check that the remainling roots are evenly spaced.
+  for (unsigned i = 1; i < N - 1; ++i) {
+    const SCEV *NewStepSCEV = SE->getMinusSCEV(SE->getSCEV(DRS.Roots[i]),
+                                               SE->getSCEV(DRS.Roots[i-1]));
+    if (NewStepSCEV != StepSCEV)
+      return false;
+  }
+
   return true;
 }
 

diff --git a/test/Transforms/LoopReroll/basic.ll b/test/Transforms/LoopReroll/basic.ll
index 6e2f2fcabf1316cdeffe69145c031bbd55862019..b415b2653ac87bfec0d952d1aa8cc039a2b8562e 100644 (file)
--- a/test/Transforms/LoopReroll/basic.ll
+++ b/test/Transforms/LoopReroll/basic.ll
@@ -785,6 +785,30 @@ bb19:                                             ; preds = %bb3
   ret void
 }
 
+define void @bad_step(i32* nocapture readnone %x) #0 {
+entry:
+  br label %for.body
+
+for.body:                                         ; preds = %for.body, %entry
+  %i.08 = phi i32 [ 0, %entry ], [ %add3, %for.body ]
+  %call = tail call i32 @foo(i32 %i.08) #1
+  %add = add nsw i32 %i.08, 2
+  %call1 = tail call i32 @foo(i32 %add) #1
+  %add2 = add nsw i32 %i.08, 3
+  %call3 = tail call i32 @foo(i32 %add2) #1
+  %add3 = add nsw i32 %i.08, 6
+  %exitcond = icmp sge i32 %add3, 500
+  br i1 %exitcond, label %for.end, label %for.body
+
+; CHECK-LABEL: @bad_step
+; CHECK: %add = add nsw i32 %i.08, 2
+; CHECK: %add2 = add nsw i32 %i.08, 3
+; CHECK: %add3 = add nsw i32 %i.08, 6
+
+for.end:                                          ; preds = %for.body
+  ret void
+}
+
 attributes #0 = { nounwind uwtable }
 attributes #1 = { nounwind }