Improve tail call elimination to handle the switch statement.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@86403 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Target/README.txt b/lib/Target/README.txt
index 7018b61..dce29b8 100644
--- a/lib/Target/README.txt
+++ b/lib/Target/README.txt
@@ -406,22 +406,6 @@
//===---------------------------------------------------------------------===//
-Tail recursion elimination is not transforming this function, because it is
-returning n, which fails the isDynamicConstant check in the accumulator
-recursion checks.
-
-long long fib(const long long n) {
- switch(n) {
- case 0:
- case 1:
- return n;
- default:
- return fib(n-1) + fib(n-2);
- }
-}
-
-//===---------------------------------------------------------------------===//
-
Tail recursion elimination should handle:
int pow2m1(int n) {
diff --git a/lib/Transforms/Scalar/TailRecursionElimination.cpp b/lib/Transforms/Scalar/TailRecursionElimination.cpp
index e059913..4119cb9 100644
--- a/lib/Transforms/Scalar/TailRecursionElimination.cpp
+++ b/lib/Transforms/Scalar/TailRecursionElimination.cpp
@@ -234,7 +234,7 @@
// We currently handle static constants and arguments that are not modified as
// part of the recursion.
//
-static bool isDynamicConstant(Value *V, CallInst *CI) {
+static bool isDynamicConstant(Value *V, CallInst *CI, ReturnInst *RI) {
if (isa<Constant>(V)) return true; // Static constants are always dyn consts
// Check to see if this is an immutable argument, if so, the value
@@ -252,6 +252,15 @@
if (CI->getOperand(ArgNo+1) == Arg)
return true;
}
+
+ // Switch cases are always constant integers. If the value is being switched
+ // on and the return is only reachable from one of its cases, it's
+ // effectively constant.
+ if (BasicBlock *UniquePred = RI->getParent()->getUniquePredecessor())
+ if (SwitchInst *SI = dyn_cast<SwitchInst>(UniquePred->getTerminator()))
+ if (SI->getCondition() == V)
+ return SI->getDefaultDest() != RI->getParent();
+
// Not a constant or immutable argument, we can't safely transform.
return false;
}
@@ -273,7 +282,7 @@
// evaluatable at the start of the initial invocation of the function,
// instead of at the end of the evaluation.
//
- if (!isDynamicConstant(RetOp, CI))
+ if (!isDynamicConstant(RetOp, CI, RI))
return 0;
if (ReturnedValue && RetOp != ReturnedValue)