#include "llvm/Support/CFG.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/raw_ostream.h"
-#include "llvm/Support/ValueHandle.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/ADT/STLExtras.h"
using namespace llvm;
return new TailCallElim();
}
-/// CanTRE - Scan the specified basic block for alloca instructions.
-/// If it contains any that are variable-sized or not in the entry block,
-/// returns false.
-static bool CanTRE(AllocaInst *AI) {
- // Because of PR962, we don't TRE allocas outside the entry block.
-
- // If this alloca is in the body of the function, or if it is a variable
- // sized allocation, we cannot tail call eliminate calls marked 'tail'
- // with this mechanism.
- BasicBlock *BB = AI->getParent();
- return BB == &BB->getParent()->getEntryBlock() &&
- isa<ConstantInt>(AI->getArraySize());
+/// AllocaMightEscapeToCalls - Return true if this alloca may be accessed by
+/// callees of this function. We only do very simple analysis right now, this
+/// could be expanded in the future to use mod/ref information for particular
+/// call sites if desired.
+static bool AllocaMightEscapeToCalls(AllocaInst *AI) {
+ // FIXME: do simple 'address taken' analysis.
+ return true;
}
-struct AllocaCaptureTracker : public CaptureTracker {
- AllocaCaptureTracker() : Captured(false) {}
-
- void tooManyUses() { Captured = true; }
-
- bool shouldExplore(Use *U) {
- Value *V = U->getUser();
- if (isa<CallInst>(V) || isa<InvokeInst>(V))
- UsesAlloca.push_back(V);
-
- return true;
- }
-
- bool captured(Use *U) {
- if (isa<ReturnInst>(U->getUser()))
- return false;
-
- Captured = true;
- return true;
- }
-
- SmallVector<WeakVH, 64> UsesAlloca;
-
- bool Captured;
-};
+/// CheckForEscapingAllocas - Scan the specified basic block for alloca
+/// instructions. If it contains any that might be accessed by calls, return
+/// true.
+static bool CheckForEscapingAllocas(BasicBlock *BB,
+ bool &CannotTCETailMarkedCall) {
+ bool RetVal = false;
+ for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I)
+ if (AllocaInst *AI = dyn_cast<AllocaInst>(I)) {
+ RetVal |= AllocaMightEscapeToCalls(AI);
+
+ // If this alloca is in the body of the function, or if it is a variable
+ // sized allocation, we cannot tail call eliminate calls marked 'tail'
+ // with this mechanism.
+ if (BB != &BB->getParent()->getEntryBlock() ||
+ !isa<ConstantInt>(AI->getArraySize()))
+ CannotTCETailMarkedCall = true;
+ }
+ return RetVal;
+}
bool TailCallElim::runOnFunction(Function &F) {
// If this function is a varargs function, we won't be able to PHI the args
bool MadeChange = false;
bool FunctionContainsEscapingAllocas = false;
- // CanTRETailMarkedCall - If false, we cannot perform TRE on tail calls
+ // CannotTCETailMarkedCall - If true, we cannot perform TCE on tail calls
// marked with the 'tail' attribute, because doing so would cause the stack
- // size to increase (real TRE would deallocate variable sized allocas, TRE
+ // size to increase (real TCE would deallocate variable sized allocas, TCE
// doesn't).
- bool CanTRETailMarkedCall = true;
-
- // Find calls that can be marked tail.
- AllocaCaptureTracker ACT;
- for (Function::iterator BB = F.begin(), EE = F.end(); BB != EE; ++BB) {
- for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I) {
- if (AllocaInst *AI = dyn_cast<AllocaInst>(I)) {
- CanTRETailMarkedCall &= CanTRE(AI);
- PointerMayBeCaptured(AI, &ACT);
- if (ACT.Captured)
- return false;
- }
- }
+ bool CannotTCETailMarkedCall = false;
+
+ // Loop over the function, looking for any returning blocks, and keeping track
+ // of whether this function has any non-trivially used allocas.
+ for (Function::iterator BB = F.begin(), E = F.end(); BB != E; ++BB) {
+ if (FunctionContainsEscapingAllocas && CannotTCETailMarkedCall)
+ break;
+
+ FunctionContainsEscapingAllocas |=
+ CheckForEscapingAllocas(BB, CannotTCETailMarkedCall);
}
- // Second pass, change any tail recursive calls to loops.
+ /// FIXME: The code generator produces really bad code when an 'escaping
+ /// alloca' is changed from being a static alloca to being a dynamic alloca.
+ /// Until this is resolved, disable this transformation if that would ever
+ /// happen. This bug is PR962.
+ if (FunctionContainsEscapingAllocas)
+ return false;
+
+ // Second pass, change any tail calls to loops.
for (Function::iterator BB = F.begin(), E = F.end(); BB != E; ++BB) {
if (ReturnInst *Ret = dyn_cast<ReturnInst>(BB->getTerminator())) {
bool Change = ProcessReturningBlock(Ret, OldEntry, TailCallsAreMarkedTail,
- ArgumentPHIs, !CanTRETailMarkedCall);
+ ArgumentPHIs,CannotTCETailMarkedCall);
if (!Change && BB->getFirstNonPHIOrDbg() == Ret)
Change = FoldReturnAndProcessPred(BB, Ret, OldEntry,
TailCallsAreMarkedTail, ArgumentPHIs,
- !CanTRETailMarkedCall);
+ CannotTCETailMarkedCall);
MadeChange |= Change;
}
}
}
}
- // Finally, if this function contains no non-escaping allocas and doesn't
- // call setjmp, mark all calls in the function as eligible for tail calls
- // (there is no stack memory for them to access).
- std::sort(ACT.UsesAlloca.begin(), ACT.UsesAlloca.end());
-
+ // Finally, if this function contains no non-escaping allocas, or calls
+ // setjmp, mark all calls in the function as eligible for tail calls
+ //(there is no stack memory for them to access).
if (!FunctionContainsEscapingAllocas && !F.callsFunctionThatReturnsTwice())
for (Function::iterator BB = F.begin(), E = F.end(); BB != E; ++BB)
for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I)
- if (CallInst *CI = dyn_cast<CallInst>(I))
- if (!std::binary_search(ACT.UsesAlloca.begin(), ACT.UsesAlloca.end(),
- CI)) {
- CI->setTailCall();
- MadeChange = true;
- }
+ if (CallInst *CI = dyn_cast<CallInst>(I)) {
+ CI->setTailCall();
+ MadeChange = true;
+ }
return MadeChange;
}
+
/// CanMoveAboveCall - Return true if it is safe to move the specified
/// instruction from after the call to before the call, assuming that all
/// instructions between the call and this instruction are movable.
; RUN: opt %s -tailcallelim -S | FileCheck %s
+; XFAIL: *
declare void @use(i8* nocapture, i8* nocapture)
-declare void @boring()
-define i8* @test1(i8* nocapture %A, i1 %cond) {
+define i8* @foo(i8* nocapture %A, i1 %cond) {
; CHECK: tailrecurse:
; CHECK: %A.tr = phi i8* [ %A, %0 ], [ %B, %cond_true ]
; CHECK: %cond.tr = phi i1 [ %cond, %0 ], [ false, %cond_true ]
cond_true:
; CHECK: cond_true:
; CHECK: br label %tailrecurse
- call i8* @test1(i8* %B, i1 false)
+ call i8* @foo(i8* %B, i1 false)
ret i8* null
cond_false:
; CHECK: cond_false
call void @use(i8* %A, i8* %B)
-; CHECK: call void @use(i8* %A.tr, i8* %B)
- call void @boring()
-; CHECK: tail call void @boring()
+; CHECK: tail call void @use(i8* %A.tr, i8* %B)
ret i8* null
; CHECK: ret i8* null
}
-
-; PR14143
-define void @test2(i8* %a, i8* %b) {
-; CHECK: @test2
-; CHECK-NOT: tail call
-; CHECK: ret void
- %c = alloca [100 x i8], align 16
- %tmp = bitcast [100 x i8]* %c to i8*
- call void @llvm.memcpy.p0i8.p0i8.i64(i8* %b, i8* %tmp, i64 100, i32 1, i1 false)
- ret void
-}
-
-declare void @llvm.memcpy.p0i8.p0i8.i64(i8*, i8*, i64, i32, i1)
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