When converting phi nodes into select instructions, we shouldn't promote PHI

nodes unless we KNOW that we are able to promote all of them.  In this case
promoting the phi to a select is silly because we will always have to do the
call conditionally.  As such, select promotion is actually a pessimization.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@16972 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/test/Transforms/SimplifyCFG/PhiNoEliminate.ll b/test/Transforms/SimplifyCFG/PhiNoEliminate.ll
new file mode 100644 (file)
index 0000000..6e7c9f5
--- /dev/null
+++ b/test/Transforms/SimplifyCFG/PhiNoEliminate.ll
@@ -0,0 +1,29 @@
+; RUN: llvm-as < %s | opt -simplifycfg | llvm-dis | not grep select
+
+;; The PHI node in this example should not be turned into a select, as we are
+;; not able to ifcvt the entire block.  As such, converting to a select just 
+;; introduces inefficiency without saving copies.
+
+int %bar(bool %C) {
+entry:
+        br bool %C, label %then, label %endif
+
+then:
+        %tmp.3 = call int %qux()
+        br label %endif
+
+endif:
+       %R = phi int [123, %entry], [12312, %then]
+       ;; stuff to disable tail duplication
+        call int %qux()
+        call int %qux()
+        call int %qux()
+        call int %qux()
+        call int %qux()
+        call int %qux()
+        call int %qux()
+        ret int %R
+}
+
+declare int %qux()
+