[LoopDeletion] Handle users in unreachable block
This is a fix for PR35884.
When we want to delete dead loop we must clean uses in unreachable blocks
otherwise we'll get an assert during deletion of instructions from the loop.
Reviewers: anna, davide
Reviewed By: anna
Subscribers: llvm-commits, lebedev.ri
Differential Revision: https://reviews.llvm.org/D41943
llvm-svn: 322357
diff --git a/llvm/lib/Transforms/Utils/LoopUtils.cpp b/llvm/lib/Transforms/Utils/LoopUtils.cpp
index a5a305e..fab989c 100644
--- a/llvm/lib/Transforms/Utils/LoopUtils.cpp
+++ b/llvm/lib/Transforms/Utils/LoopUtils.cpp
@@ -1356,6 +1356,32 @@
DT->deleteEdge(Preheader, L->getHeader());
}
+ // Given LCSSA form is satisfied, we should not have users of instructions
+ // within the dead loop outside of the loop. However, LCSSA doesn't take
+ // unreachable uses into account. We handle them here.
+ // We could do it after drop all references (in this case all users in the
+ // loop will be already eliminated and we have less work to do but according
+ // to API doc of User::dropAllReferences only valid operation after dropping
+ // references, is deletion. So let's substitute all usages of
+ // instruction from the loop with undef value of corresponding type first.
+ for (auto *Block : L->blocks())
+ for (Instruction &I : *Block) {
+ auto *Undef = UndefValue::get(I.getType());
+ for (Value::use_iterator UI = I.use_begin(), E = I.use_end(); UI != E;) {
+ Use &U = *UI;
+ ++UI;
+ if (auto *Usr = dyn_cast<Instruction>(U.getUser()))
+ if (L->contains(Usr->getParent()))
+ continue;
+ // If we have a DT then we can check that uses outside a loop only in
+ // unreachable block.
+ if (DT)
+ assert(!DT->isReachableFromEntry(U) &&
+ "Unexpected user in reachable block");
+ U.set(Undef);
+ }
+ }
+
// Remove the block from the reference counting scheme, so that we can
// delete it freely later.
for (auto *Block : L->blocks())
diff --git a/llvm/test/Transforms/LoopDeletion/use-in-unreachable.ll b/llvm/test/Transforms/LoopDeletion/use-in-unreachable.ll
new file mode 100644
index 0000000..ff7bc75
--- /dev/null
+++ b/llvm/test/Transforms/LoopDeletion/use-in-unreachable.ll
@@ -0,0 +1,24 @@
+; RUN: opt < %s -loop-deletion -S | FileCheck %s
+
+; Checking that possible users of instruction from the loop in
+; unreachable blocks are handled.
+
+define i64 @foo() {
+entry:
+ br label %invloop
+; CHECK-LABEL-NOT: invloop
+invloop:
+ %indvar1 = phi i64 [ 3, %entry ], [ %indvar2, %invloop_iter ]
+ %check = icmp ult i64 %indvar1, 400
+ br i1 %check, label %invloop_iter, label %loopexit
+invloop_iter:
+ %indvar2 = add i64 %indvar1, 1
+ %baddef = add i64 0, 0
+ br label %invloop
+loopexit:
+ ret i64 0
+deadcode:
+; CHECK-LABEL: deadcode
+; CHECK: ret i64 undef
+ ret i64 %baddef
+}