LSR crashes on an empty IVUsers list.

rdar://9786536


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@135644 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Transforms/Scalar/LoopStrengthReduce.cpp

@@ -3740,6 +3740,9 @@ LSRInstance::LSRInstance(const TargetLowering *tli, Loop *l, Pass *P)
   OptimizeShadowIV();
   OptimizeLoopTermCond();
 
+  // If loop preparation eliminates all interesting IV users, bail.
+  if (IU.empty()) return;
+
   // Start collecting data and preparing for the solver.
   CollectInterestingTypesAndFactors();
   CollectFixupsAndInitialFormulae();

test/Transforms/LoopStrengthReduce/2011-07-20-DoubleIV.ll

@@ -0,0 +1,24 @@
+; RUN: opt < %s -loop-reduce -S | FileCheck %s
+;
+; Test LSR's OptimizeShadowIV. Handle a floating-point IV with a
+; nonzero initial value.
+; rdar://9786536
+
+; First, make sure LSR doesn't crash on an empty IVUsers list.
+; CHECK: @dummyIV
+; CHECK-NOT: phi
+; CHECK-NOT: sitofp
+; CHECK: br
+define void @dummyIV() nounwind {
+entry:
+  br label %loop
+
+loop:
+  %i.01 = phi i32 [ -39, %entry ], [ %inc, %loop ]
+  %conv7 = sitofp i32 %i.01 to double
+  %inc = add nsw i32 %i.01, 1
+  br i1 undef, label %loop, label %for.end
+
+for.end:
+  unreachable
+}