[JumpThreading] Split select that has constant conditions coming from the PHI node

Look for PHI/Select in the same BB of the form

bb:
  %p = phi [false, %bb1], [true, %bb2], [false, %bb3], [true, %bb4], ...
  %s = select p, trueval, falseval

And expand the select into a branch structure. This later enables
jump-threading over bb in this pass.

Using the similar approach of SimplifyCFG::FoldCondBranchOnPHI(), unfold
select if the associated PHI has at least one constant.  If the unfolded
select is not jump-threaded, it will be folded again in the later
optimizations.

llvm-svn: 257198

1 files changed, 37 insertions, 0 deletions

diff --git a/llvm/test/Transforms/JumpThreading/select.ll b/llvm/test/Transforms/JumpThreading/select.ll
index 595cacbcbf5..6a3cf7edd7d 100644
--- a/llvm/test/Transforms/JumpThreading/select.ll
+++ b/llvm/test/Transforms/JumpThreading/select.ll
@@ -250,3 +250,40 @@ if.end:                                           ; preds = %if.then, %cond.end4
 ; CHECK: br i1 %cmp6, label %if.then, label %if.end
 ; CHECK: br label %if.end
 }
+
+
+define i32 @unfold3(i32 %u, i32 %v, i32 %w, i32 %x, i32 %y, i32 %z, i32 %j) nounwind {
+entry:
+  %add3 = add nsw i32 %j, 2
+  %cmp.i = icmp slt i32 %u, %v
+  br i1 %cmp.i, label %.exit, label %cond.false.i
+
+cond.false.i:                                     ; preds = %entry
+  %cmp4.i = icmp sgt i32 %u, %v
+  br i1 %cmp4.i, label %.exit, label %cond.false.6.i
+
+cond.false.6.i:                                   ; preds = %cond.false.i
+  %cmp8.i = icmp slt i32 %w, %x
+  br i1 %cmp8.i, label %.exit, label %cond.false.10.i
+
+cond.false.10.i:                                  ; preds = %cond.false.6.i
+  %cmp13.i = icmp sgt i32 %w, %x
+  br i1 %cmp13.i, label %.exit, label %cond.false.15.i
+
+cond.false.15.i:                                  ; preds = %cond.false.10.i
+  %phitmp = icmp sge i32 %y, %z
+  br label %.exit
+
+.exit:                                  ; preds = %entry, %cond.false.i, %cond.false.6.i, %cond.false.10.i, %cond.false.15.i
+  %cond23.i = phi i1 [ false, %entry ], [ true, %cond.false.i ], [ false, %cond.false.6.i ], [ %phitmp, %cond.false.15.i ], [ true, %cond.false.10.i ]
+  %j.add3 = select i1 %cond23.i, i32 %j, i32 %add3
+  ret i32 %j.add3
+
+; CHECK-LABEL: @unfold3
+; CHECK: br i1 %cmp.i, label %.exit.thread2, label %cond.false.i 
+; CHECK: br i1 %cmp4.i, label %.exit.thread, label %cond.false.6.i
+; CHECK: br i1 %cmp8.i, label %.exit.thread2, label %cond.false.10.i
+; CHECK: br i1 %cmp13.i, label %.exit.thread, label %.exit
+; CHECK: br i1 %phitmp, label %.exit.thread, label %.exit.thread2
+; CHECK: br label %.exit.thread2
+}