In LVI(Lazy Value Info), originally value on a BB can only be caculated once,

and the lattice will be updated to be a state other than "undefined". This
limiation could miss some opportunities of lowering "overdefined" to be an
even accurate value. So this patch ask the algorithm to try to lower the
lattice value again even if the value has been lowered to be "overdefined".

llvm-svn: 215343

1 files changed, 33 insertions, 0 deletions

diff --git a/llvm/test/Transforms/JumpThreading/jump_threading.ll b/llvm/test/Transforms/JumpThreading/jump_threading.ll
new file mode 100644
index 00000000000..f5a0ead3d90
--- /dev/null
+++ b/llvm/test/Transforms/JumpThreading/jump_threading.ll
@@ -0,0 +1,33 @@
+; RUN: opt < %s -jump-threading -S | FileCheck %s
+
+define i32 @test_jump_threading(i32* %arg1, i32 %arg2) {
+entry:
+  %cmp = icmp slt i32 %arg2, 0
+  br i1 %cmp, label %land.lhs.true, label %lor.rhs
+
+land.lhs.true:
+  %ident = getelementptr inbounds i32 * %arg1, i64 0
+  %0 = load i32* %ident, align 4
+  %cmp1 = icmp eq i32 %0, 1
+  br i1 %cmp1, label %lor.end, label %lor.rhs
+
+; CHECK: br i1 %cmp1, label %lor.end, label %lor.rhs.thread
+
+; CHECK: lor.rhs.thread:
+; CHECK-NEXT: br label %lor.end
+
+lor.rhs:
+  %cmp2 = icmp sgt i32 %arg2, 0
+  br i1 %cmp2, label %land.rhs, label %lor.end
+
+land.rhs:
+  %ident3 = getelementptr inbounds i32 * %arg1, i64 0
+  %1 = load i32* %ident3, align 4
+  %cmp4 = icmp eq i32 %1, 2
+  br label %lor.end
+
+lor.end:
+  %2 = phi i1 [ true, %land.lhs.true ], [ false, %lor.rhs ], [ %cmp4, %land.rhs ]
+  %lor.ext = zext i1 %2 to i32
+  ret i32 %lor.ext
+}