Disable inlining of recursive calls. It can complicate tailcallelim and

dependent analyses, and increase code size, so doing it profitably would
require more complex heuristics.

llvm-svn: 101471

llvm/lib/Analysis/InlineCost.cpp

@@ -263,6 +263,13 @@ InlineCost InlineCostAnalyzer::getInlineCost(CallSite CS,
       CS.isNoInline())
     return llvm::InlineCost::getNever();
 
+  // Don't inline directly recursive calls, for now. Inlining a directly
+  // recursive call is effectively unrolling a loop, so it calls for different
+  // heuristics, which aren't implemented yet. Until then, err on the
+  // conservative side.
+  if (Callee == Caller)
+    return llvm::InlineCost::getNever();
+
   // InlineCost - This value measures how good of an inline candidate this call
   // site is to inline.  A lower inline cost make is more likely for the call to
   // be inlined.  This value may go negative.

llvm/test/Transforms/Inline/tail-recursion.ll

@@ -0,0 +1,29 @@
+; RUN: opt -inline -tailcallelim -indvars -loop-deletion -S < %s | FileCheck %s
+
+; Inline shouldn't inline foo into itself because it's a tailcallelim
+; candidate. Tailcallelim should convert the call into a loop. Indvars
+; should calculate the exit value, making the loop dead. Loop deletion
+; should delete the loop.
+; PR6842
+
+;      CHECK: define i32 @bar() nounwind {
+; CHECK-NEXT:     ret i32 10000
+; CHECK-NEXT: }
+
+define internal i32 @foo(i32 %x) nounwind {
+  %i = add i32 %x, 1                              ; <i32> [#uses=3]
+  %a = icmp slt i32 %i, 10000                     ; <i1> [#uses=1]
+  br i1 %a, label %more, label %done
+
+done:                                             ; preds = %0
+  ret i32 %i
+
+more:                                             ; preds = %0
+  %z = tail call i32 @foo(i32 %i)                  ; <i32> [#uses=1]
+  ret i32 %z
+}
+
+define i32 @bar() nounwind {
+  %z = call i32 @foo(i32 0)                        ; <i32> [#uses=1]
+  ret i32 %z
+}