[llvm-commits] [llvm] r166407 - in /llvm/trunk: lib/Transforms/Scalar/TailRecursionElimination.cpp test/Transforms/TailCallElim/nocapture.ll
Nick Lewycky
nicholas at mxc.ca
Sun Oct 21 20:03:53 PDT 2012
Author: nicholas
Date: Sun Oct 21 22:03:52 2012
New Revision: 166407
URL: http://llvm.org/viewvc/llvm-project?rev=166407&view=rev
Log:
Reapply r166405, teaching tailcallelim to be smarter about nocapture, with a
very small but very important bugfix:
bool shouldExplore(Use *U) {
Value *V = U->get();
if (isa<CallInst>(V) || isa<InvokeInst>(V))
[...]
should have read:
bool shouldExplore(Use *U) {
Value *V = U->getUser();
if (isa<CallInst>(V) || isa<InvokeInst>(V))
Fixes PR14143!
Modified:
llvm/trunk/lib/Transforms/Scalar/TailRecursionElimination.cpp
llvm/trunk/test/Transforms/TailCallElim/nocapture.ll
Modified: llvm/trunk/lib/Transforms/Scalar/TailRecursionElimination.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Scalar/TailRecursionElimination.cpp?rev=166407&r1=166406&r2=166407&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/Scalar/TailRecursionElimination.cpp (original)
+++ llvm/trunk/lib/Transforms/Scalar/TailRecursionElimination.cpp Sun Oct 21 22:03:52 2012
@@ -69,6 +69,7 @@
#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;
@@ -117,35 +118,46 @@
return new TailCallElim();
}
-/// 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;
-}
+/// 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.
-/// 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;
+ // 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());
}
+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;
+};
+
bool TailCallElim::runOnFunction(Function &F) {
// If this function is a varargs function, we won't be able to PHI the args
// right, so don't even try to convert it...
@@ -157,38 +169,34 @@
bool MadeChange = false;
bool FunctionContainsEscapingAllocas = false;
- // CannotTCETailMarkedCall - If true, we cannot perform TCE on tail calls
+ // CanTRETailMarkedCall - If false, we cannot perform TRE on tail calls
// marked with the 'tail' attribute, because doing so would cause the stack
- // size to increase (real TCE would deallocate variable sized allocas, TCE
+ // size to increase (real TRE would deallocate variable sized allocas, TRE
// doesn't).
- 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;
+ bool CanTRETailMarkedCall = true;
- FunctionContainsEscapingAllocas |=
- CheckForEscapingAllocas(BB, CannotTCETailMarkedCall);
+ // 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;
+ }
+ }
}
- /// 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.
+ // Second pass, change any tail recursive 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,CannotTCETailMarkedCall);
+ ArgumentPHIs, !CanTRETailMarkedCall);
if (!Change && BB->getFirstNonPHIOrDbg() == Ret)
Change = FoldReturnAndProcessPred(BB, Ret, OldEntry,
TailCallsAreMarkedTail, ArgumentPHIs,
- CannotTCETailMarkedCall);
+ !CanTRETailMarkedCall);
MadeChange |= Change;
}
}
@@ -210,21 +218,24 @@
}
}
- // 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).
+ // 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());
+
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)) {
- CI->setTailCall();
- MadeChange = true;
- }
+ if (CallInst *CI = dyn_cast<CallInst>(I))
+ if (!std::binary_search(ACT.UsesAlloca.begin(), ACT.UsesAlloca.end(),
+ CI)) {
+ 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.
Modified: llvm/trunk/test/Transforms/TailCallElim/nocapture.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/TailCallElim/nocapture.ll?rev=166407&r1=166406&r2=166407&view=diff
==============================================================================
--- llvm/trunk/test/Transforms/TailCallElim/nocapture.ll (original)
+++ llvm/trunk/test/Transforms/TailCallElim/nocapture.ll Sun Oct 21 22:03:52 2012
@@ -1,9 +1,9 @@
; RUN: opt %s -tailcallelim -S | FileCheck %s
-; XFAIL: *
declare void @use(i8* nocapture, i8* nocapture)
+declare void @boring()
-define i8* @foo(i8* nocapture %A, i1 %cond) {
+define i8* @test1(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 ]
@@ -14,12 +14,27 @@
cond_true:
; CHECK: cond_true:
; CHECK: br label %tailrecurse
- call i8* @foo(i8* %B, i1 false)
+ call i8* @test1(i8* %B, i1 false)
ret i8* null
cond_false:
; CHECK: cond_false
call void @use(i8* %A, i8* %B)
-; CHECK: tail call void @use(i8* %A.tr, i8* %B)
+; CHECK: call void @use(i8* %A.tr, i8* %B)
+ call void @boring()
+; CHECK: tail call void @boring()
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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