Don't skip debug instructions when looking for the insertion point of

the cast. If we do, we can end up with

   inst1
   ---------------  < Insertion point
   dbg inst
   new inst

instead of the desired

   inst1
   new inst
   ---------------  < Insertion point
   dbg inst

Another option would be for InsertNoopCastOfTo (or its callers) to move the
insertion point and we would end up with

   inst1
   dbg inst
   new inst
   ---------------  < Insertion point

but that complicates the callers. This fixes PR12018 (and firefox's build).

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@150884 91177308-0d34-0410-b5e6-96231b3b80d8

2 files changed, 46 insertions, 5 deletions

diff --git a/lib/Analysis/ScalarEvolutionExpander.cpp b/lib/Analysis/ScalarEvolutionExpander.cpp
index f559889799..58181fb09f 100644
--- a/lib/Analysis/ScalarEvolutionExpander.cpp
+++ b/lib/Analysis/ScalarEvolutionExpander.cpp
@@ -31,6 +31,12 @@ using namespace llvm;
 Value *SCEVExpander::ReuseOrCreateCast(Value *V, Type *Ty,
                                        Instruction::CastOps Op,
                                        BasicBlock::iterator IP) {
+  // All new or reused instructions must strictly dominate the Builder's
+  // InsertPt to ensure that the expression's expansion dominates its uses.
+  // Assert that the requested insertion point works at least for new
+  // instructions.
+  assert(SE.DT->dominates(IP, Builder.GetInsertPoint()));
+
   // Check to see if there is already a cast!
   for (Value::use_iterator UI = V->use_begin(), E = V->use_end();
        UI != E; ++UI) {
@@ -38,9 +44,7 @@ Value *SCEVExpander::ReuseOrCreateCast(Value *V, Type *Ty,
     if (U->getType() == Ty)
       if (CastInst *CI = dyn_cast<CastInst>(U))
         if (CI->getOpcode() == Op) {
-          // If the cast isn't where we want it, fix it. All new or reused
-          // instructions must strictly dominate the Builder's InsertPt to
-          // ensure that the expression's expansion dominates its uses.
+          // If the cast isn't where we want it, fix it.
           if (BasicBlock::iterator(CI) != IP
               || IP == Builder.GetInsertPoint()) {
             // Create a new cast, and leave the old cast in place in case
@@ -124,8 +128,7 @@ Value *SCEVExpander::InsertNoopCastOfTo(Value *V, Type *Ty) {
   BasicBlock::iterator IP = I; ++IP;
   if (InvokeInst *II = dyn_cast<InvokeInst>(I))
     IP = II->getNormalDest()->begin();
-  while (isa<PHINode>(IP) || isa<DbgInfoIntrinsic>(IP) ||
-         isa<LandingPadInst>(IP))
+  while (isa<PHINode>(IP) || isa<LandingPadInst>(IP))
     ++IP;
   return ReuseOrCreateCast(I, Ty, Op, IP);
 }
diff --git a/test/Transforms/LoopStrengthReduce/pr12018.ll b/test/Transforms/LoopStrengthReduce/pr12018.ll
new file mode 100644
index 0000000000..ee7b1e8883
--- /dev/null
+++ b/test/Transforms/LoopStrengthReduce/pr12018.ll
@@ -0,0 +1,38 @@
+; RUN: opt < %s -loop-reduce
+
+target datalayout = "e-p:32:32:32-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:32:64-f32:32:32-f64:32:64-v64:64:64-v128:128:128-a0:0:64-f80:128:128-n8:16:32-S128"
+
+%struct.nsTArray = type { i8 }
+%struct.nsTArrayHeader = type { i32 }
+
+define void @_Z6foobarR8nsTArray(%struct.nsTArray* %aValues, i32 %foo, %struct.nsTArrayHeader* %bar) nounwind {
+entry:
+  br label %for.body
+
+for.body:                                         ; preds = %_ZN8nsTArray9ElementAtEi.exit, %entry
+  %i.06 = phi i32 [ %add, %_ZN8nsTArray9ElementAtEi.exit ], [ 0, %entry ]
+  %call.i = call %struct.nsTArrayHeader* @_ZN8nsTArray4Hdr2Ev() nounwind
+  %add.ptr.i = getelementptr inbounds %struct.nsTArrayHeader* %call.i, i32 1
+  %tmp = bitcast %struct.nsTArrayHeader* %add.ptr.i to %struct.nsTArray*
+  %arrayidx = getelementptr inbounds %struct.nsTArray* %tmp, i32 %i.06
+  %add = add nsw i32 %i.06, 1
+  call void @llvm.dbg.value(metadata !{%struct.nsTArray* %aValues}, i64 0, metadata !0) nounwind
+  br label %_ZN8nsTArray9ElementAtEi.exit
+
+_ZN8nsTArray9ElementAtEi.exit:                    ; preds = %for.body
+  %arrayidx.i = getelementptr inbounds %struct.nsTArray* %tmp, i32 %add
+  call void @_ZN11nsTArray15ComputeDistanceERKS_Rd(%struct.nsTArray* %arrayidx, %struct.nsTArray* %arrayidx.i) nounwind
+  %cmp = icmp slt i32 %add, %foo
+  br i1 %cmp, label %for.body, label %for.end
+
+for.end:                                          ; preds = %_ZN8nsTArray9ElementAtEi.exit
+  ret void
+}
+
+declare void @_ZN11nsTArray15ComputeDistanceERKS_Rd(%struct.nsTArray*, %struct.nsTArray*)
+
+declare %struct.nsTArrayHeader* @_ZN8nsTArray4Hdr2Ev()
+
+declare void @llvm.dbg.value(metadata, i64, metadata) nounwind readnone
+
+!0 = metadata !{i32 786689}                       ; [ DW_TAG_arg_variable ]