Improve LSR's dead-phi detection to handle use-def cycles

with more than two nodes.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@52617 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 21 insertions, 0 deletions

diff --git a/test/Transforms/LoopStrengthReduce/dead-phi.ll b/test/Transforms/LoopStrengthReduce/dead-phi.ll
new file mode 100644
index 0000000000..a6aafa911d
--- /dev/null
+++ b/test/Transforms/LoopStrengthReduce/dead-phi.ll
@@ -0,0 +1,21 @@
+; RUN: llvm-as < %s | opt -loop-reduce | llvm-dis | grep phi | count 1
+
+define void @foo(i32 %n) {
+entry:
+  br label %loop
+
+loop:
+  %i = phi i32 [ 0, %entry ], [ %i.next, %loop ]
+
+  ; These three instructions form an isolated cycle and can be deleted.
+  %j = phi i32 [ 0, %entry ], [ %j.y, %loop ]
+  %j.x = add i32 %j, 1
+  %j.y = mul i32 %j.x, 2
+
+  %i.next = add i32 %i, 1
+  %c = icmp ne i32 %i.next, %n
+  br i1 %c, label %loop, label %exit
+
+exit:
+  ret void
+}