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In guaranteed tailcall mode, don't decline the tailcall optimization 

for blocks ending in "unreachable".

llvm-svn: 95565
This commit is contained in:
Dan Gohman 2010-02-08 20:34:14 +00:00
parent 3464a5b609
commit bd374da130
2 changed files with 14 additions and 8 deletions
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17
llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
View File

@ -4205,13 +4205,16 @@ isInTailCallPosition(CallSite CS, Attributes CalleeRetAttr,
const ReturnInst *Ret = dyn_cast<ReturnInst>(Term);
const Function *F = ExitBB->getParent();
// The block must end in a return statement.
// FIXME: Disallow tailcall if the block ends in an unreachable for now.
// The way tailcall optimization is currently implemented means it will
// add an epilogue followed by a jump. That is not profitable. Also, if
// the callee is a special function (e.g. longjmp on x86), it can end up
// causing miscompilation that has not been fully understood.
if (!Ret) return false;
// The block must end in a return statement or unreachable.
//
// FIXME: Decline tailcall if it's not guaranteed and if the block ends in
// an unreachable, for now. The way tailcall optimization is currently
// implemented means it will add an epilogue followed by a jump. That is
// not profitable. Also, if the callee is a special function (e.g.
// longjmp on x86), it can end up causing miscompilation that has not
// been fully understood.
if (!Ret &&
(!GuaranteedTailCallOpt || !isa<UnreachableInst>(Term))) return false;
// If I will have a chain, make sure no other instruction that will have a
// chain interposes between I and the return.

5
llvm/test/CodeGen/X86/tailcall1.ll
View File

@ -1,4 +1,7 @@
; RUN: llc < %s -march=x86 -tailcallopt | grep TAILCALL | count 4
; RUN: llc < %s -march=x86 -tailcallopt | grep TAILCALL | count 5
; With -tailcallopt, CodeGen guarantees a tail call optimization
; for all of these.
declare fastcc i32 @tailcallee(i32 %a1, i32 %a2, i32 %a3, i32 %a4)