1 files changed, 99 insertions, 0 deletions
diff --git a/llvm/test/Transforms/JumpThreading/header-succ.ll b/llvm/test/Transforms/JumpThreading/header-succ.ll
new file mode 100644
index 00000000000..859d44cff29
--- /dev/null
+++ b/llvm/test/Transforms/JumpThreading/header-succ.ll
@@ -0,0 +1,99 @@
+; RUN: opt -S -jump-threading < %s | FileCheck %s
+
+; Check that the heuristic for avoiding accidental introduction of irreducible
+; loops doesn't also prevent us from threading simple constructs where this
+; isn't a problem.
+
+declare void @opaque_body()
+
+define void @jump_threading_loopheader() {
+; CHECK-LABEL: @jump_threading_loopheader
+top:
+    br label %entry
+
+entry:
+    %ind = phi i32 [0, %top], [%nextind, %latch]
+    %nextind = add i32 %ind, 1
+    %cmp = icmp ule i32 %ind, 10
+; CHECK: br i1 %cmp, label %latch, label %exit
+    br i1 %cmp, label %body, label %latch
+
+body:
+    call void @opaque_body()
+; CHECK: br label %entry
+    br label %latch
+
+latch:
+    %cond = phi i2 [1, %entry], [2, %body]
+    switch i2 %cond, label %unreach [
+        i2 2, label %entry
+        i2 1, label %exit
+    ]
+
+unreach:
+    unreachable
+
+exit:
+    ret void
+}
+
+; We also need to check the opposite order of the branches, in the switch
+; instruction because jump-threading relies on that to decide which edge to
+; try to thread first.
+define void @jump_threading_loopheader2() {
+; CHECK-LABEL: @jump_threading_loopheader2
+top:
+    br label %entry
+
+entry:
+    %ind = phi i32 [0, %top], [%nextind, %latch]
+    %nextind = add i32 %ind, 1
+    %cmp = icmp ule i32 %ind, 10
+; CHECK: br i1 %cmp, label %exit, label %latch
+    br i1 %cmp, label %body, label %latch
+
+body:
+    call void @opaque_body()
+; CHECK: br label %entry
+    br label %latch
+
+latch:
+    %cond = phi i2 [1, %entry], [2, %body]
+    switch i2 %cond, label %unreach [
+        i2 1, label %entry
+        i2 2, label %exit
+    ]
+
+unreach:
+    unreachable
+
+exit:
+    ret void
+}
+
+; Check if we can handle undef branch condition.
+define void @jump_threading_loopheader3() {
+; CHECK-LABEL: @jump_threading_loopheader3
+top:
+    br label %entry
+
+entry:
+    %ind = phi i32 [0, %top], [%nextind, %latch]
+    %nextind = add i32 %ind, 1
+    %cmp = icmp ule i32 %ind, 10
+; CHECK: br i1 %cmp, label %latch, label %exit
+    br i1 %cmp, label %body, label %latch
+
+body:
+    call void @opaque_body()
+; CHECK: br label %entry
+    br label %latch
+
+latch:
+   %phi = phi i32 [undef, %entry], [0, %body]
+   %cmp1 = icmp eq i32 %phi, 0
+   br i1 %cmp1, label %entry, label %exit
+
+exit:
+    ret void
+}