Dan recently disabled recursive inlining within a function, but we

were still inlining self-recursive functions into other functions.

Inlining a recursive function into itself has the potential to
reduce recursion depth by a factor of 2, inlining a recursive
function into something else reduces recursion depth by exactly 
1.  Since inlining a recursive function into something else is a
weird form of loop peeling, turn this off.

The deleted testcase was added by Dale in r62107, since then
we're leaning towards not inlining recursive stuff ever.  In any
case, if we like inlining recursive stuff, it should be done 
within the recursive function itself to get the algorithm 
recursion depth win.

llvm-svn: 102798

1 files changed, 32 insertions, 0 deletions

diff --git a/llvm/test/Transforms/Inline/noinline-recursive-fn.ll b/llvm/test/Transforms/Inline/noinline-recursive-fn.ll
new file mode 100644
index 00000000000..dcae0243300
--- /dev/null
+++ b/llvm/test/Transforms/Inline/noinline-recursive-fn.ll
@@ -0,0 +1,32 @@
+; The inliner should never inline recursive functions into other functions.
+; This effectively is just peeling off the first iteration of a loop, and the
+; inliner heuristics are not set up for this.
+
+; RUN: opt -inline %s -S | grep "call void @foo(i32 42)"
+
+target datalayout = "e-p:64:64:64-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:64:64-f32:32:32-f64:64:64-v64:64:64-v128:128:128-a0:0:64-s0:64:64-f80:128:128-n8:16:32:64"
+target triple = "x86_64-apple-darwin10.3"
+
+@g = common global i32 0                          ; <i32*> [#uses=1]
+
+define internal void @foo(i32 %x) nounwind ssp {
+entry:
+  %"alloca point" = bitcast i32 0 to i32          ; <i32> [#uses=0]
+  %0 = icmp slt i32 %x, 0                         ; <i1> [#uses=1]
+  br i1 %0, label %return, label %bb
+
+bb:                                               ; preds = %entry
+  %1 = sub nsw i32 %x, 1                          ; <i32> [#uses=1]
+  call void @foo(i32 %1) nounwind ssp
+  volatile store i32 1, i32* @g, align 4
+  ret void
+
+return:                                           ; preds = %entry
+  ret void
+}
+
+define void @bonk() nounwind ssp {
+entry:
+  call void @foo(i32 42) nounwind ssp
+  ret void
+}