Revision 14d665b3e84ac3164977b801b0003efe5d754d1a authored by Chris Lattner on 17 January 2016, 20:40:43 UTC, committed by Doug Gregor on 25 January 2016, 18:55:45 UTC
1 parent f2cd3f0
SILGenEpilog.cpp
//===--- SILGenEpilog.cpp - Function epilogue emission --------------------===//
//
// This source file is part of the Swift.org open source project
//
// Copyright (c) 2014 - 2016 Apple Inc. and the Swift project authors
// Licensed under Apache License v2.0 with Runtime Library Exception
//
// See http://swift.org/LICENSE.txt for license information
// See http://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
//
//===----------------------------------------------------------------------===//
#include "SILGen.h"
#include "SILGenFunction.h"
#include "ASTVisitor.h"
#include "swift/SIL/SILArgument.h"
using namespace swift;
using namespace Lowering;
void SILGenFunction::prepareEpilog(Type resultType, bool isThrowing,
CleanupLocation CleanupL) {
auto *epilogBB = createBasicBlock();
// If we have a non-null, non-void, non-address-only return type, receive the
// return value via a BB argument.
NeedsReturn = resultType && !resultType->isVoid();
if (NeedsReturn) {
auto &resultTI = getTypeLowering(resultType);
if (!resultTI.isAddressOnly())
new (F.getModule()) SILArgument(epilogBB, resultTI.getLoweredType());
}
ReturnDest = JumpDest(epilogBB, getCleanupsDepth(), CleanupL);
if (isThrowing) {
prepareRethrowEpilog(CleanupL);
}
}
void SILGenFunction::prepareRethrowEpilog(CleanupLocation cleanupLoc) {
auto exnType = SILType::getExceptionType(getASTContext());
SILBasicBlock *rethrowBB = createBasicBlock(FunctionSection::Postmatter);
new (F.getModule()) SILArgument(rethrowBB, exnType);
ThrowDest = JumpDest(rethrowBB, getCleanupsDepth(), cleanupLoc);
}
std::pair<Optional<SILValue>, SILLocation>
SILGenFunction::emitEpilogBB(SILLocation TopLevel) {
assert(ReturnDest.getBlock() && "no epilog bb prepared?!");
SILBasicBlock *epilogBB = ReturnDest.getBlock();
SILLocation ImplicitReturnFromTopLevel =
ImplicitReturnLocation::getImplicitReturnLoc(TopLevel);
SILValue returnValue;
Optional<SILLocation> returnLoc = None;
// If the current BB isn't terminated, and we require a return, then we
// are not allowed to fall off the end of the function and can't reach here.
if (NeedsReturn && B.hasValidInsertionPoint())
B.createUnreachable(ImplicitReturnFromTopLevel);
if (epilogBB->pred_empty()) {
bool hadArg = !epilogBB->bbarg_empty();
// If the epilog was not branched to at all, kill the BB and
// just emit the epilog into the current BB.
while (!epilogBB->empty())
epilogBB->back().eraseFromParent();
eraseBasicBlock(epilogBB);
// If the current bb is terminated then the epilog is just unreachable.
if (!B.hasValidInsertionPoint())
return { None, TopLevel };
// We emit the epilog at the current insertion point.
assert(!hadArg && "NeedsReturn is false but epilog had argument?!");
(void)hadArg;
returnLoc = ImplicitReturnFromTopLevel;
} else if (std::next(epilogBB->pred_begin()) == epilogBB->pred_end()
&& !B.hasValidInsertionPoint()) {
// If the epilog has a single predecessor and there's no current insertion
// point to fall through from, then we can weld the epilog to that
// predecessor BB.
bool needsArg = false;
if (!epilogBB->bbarg_empty()) {
assert(epilogBB->bbarg_size() == 1 && "epilog should take 0 or 1 args");
needsArg = true;
}
// Steal the branch argument as the return value if present.
SILBasicBlock *pred = *epilogBB->pred_begin();
BranchInst *predBranch = cast<BranchInst>(pred->getTerminator());
assert(predBranch->getArgs().size() == (needsArg ? 1 : 0) &&
"epilog predecessor arguments does not match block params");
if (needsArg) {
returnValue = predBranch->getArgs()[0];
// RAUW the old BB argument (if any) with the new value.
SILValue(*epilogBB->bbarg_begin(),0).replaceAllUsesWith(returnValue);
}
// If we are optimizing, we should use the return location from the single,
// previously processed, return statement if any.
if (predBranch->getLoc().is<ReturnLocation>()) {
returnLoc = predBranch->getLoc();
} else {
returnLoc = ImplicitReturnFromTopLevel;
}
// Kill the branch to the now-dead epilog BB.
pred->erase(predBranch);
// Move any instructions from the EpilogBB to the end of the 'pred' block.
pred->spliceAtEnd(epilogBB);
// Finally we can erase the epilog BB.
eraseBasicBlock(epilogBB);
// Emit the epilog into its former predecessor.
B.setInsertionPoint(pred);
} else {
// Move the epilog block to the end of the ordinary section.
auto endOfOrdinarySection =
(StartOfPostmatter ? SILFunction::iterator(StartOfPostmatter) : F.end());
B.moveBlockTo(epilogBB, endOfOrdinarySection);
// Emit the epilog into the epilog bb. Its argument is the return value.
if (!epilogBB->bbarg_empty()) {
assert(epilogBB->bbarg_size() == 1 && "epilog should take 0 or 1 args");
returnValue = epilogBB->bbarg_begin()[0];
}
// If we are falling through from the current block, the return is implicit.
B.emitBlock(epilogBB, ImplicitReturnFromTopLevel);
}
// Emit top-level cleanups into the epilog block.
assert(!Cleanups.hasAnyActiveCleanups(getCleanupsDepth(),
ReturnDest.getDepth()) &&
"emitting epilog in wrong scope");
auto cleanupLoc = CleanupLocation::get(TopLevel);
Cleanups.emitCleanupsForReturn(cleanupLoc);
// If the return location is known to be that of an already
// processed return, use it. (This will get triggered when the
// epilog logic is simplified.)
//
// Otherwise make the ret instruction part of the cleanups.
if (!returnLoc) returnLoc = cleanupLoc;
return { returnValue, *returnLoc };
}
SILLocation SILGenFunction::
emitEpilog(SILLocation TopLevel, bool UsesCustomEpilog) {
Optional<SILValue> maybeReturnValue;
SILLocation returnLoc(TopLevel);
std::tie(maybeReturnValue, returnLoc) = emitEpilogBB(TopLevel);
SILBasicBlock *ResultBB = nullptr;
if (!maybeReturnValue) {
// Nothing to do.
} else if (UsesCustomEpilog) {
// If the epilog is reachable, and the caller provided an epilog, just
// remember the block so the caller can continue it.
ResultBB = B.getInsertionBB();
assert(ResultBB && "Didn't have an epilog block?");
B.clearInsertionPoint();
} else {
// Otherwise, if the epilog block is reachable, return the return value.
SILValue returnValue = *maybeReturnValue;
// Return () if no return value was given.
if (!returnValue)
returnValue = emitEmptyTuple(CleanupLocation::get(TopLevel));
B.createReturn(returnLoc, returnValue);
}
emitRethrowEpilog(TopLevel);
if (ResultBB)
B.setInsertionPoint(ResultBB);
return returnLoc;
}
void SILGenFunction::emitRethrowEpilog(SILLocation topLevel) {
assert(!B.hasValidInsertionPoint());
// If we don't have a rethrow destination, we're done.
if (!ThrowDest.isValid())
return;
// If the rethrow destination isn't used, we're done.
SILBasicBlock *rethrowBB = ThrowDest.getBlock();
if (rethrowBB->pred_empty()) {
ThrowDest = JumpDest::invalid();
eraseBasicBlock(rethrowBB);
return;
}
SILLocation throwLoc = topLevel;
SILValue exn = rethrowBB->bbarg_begin()[0];
bool reposition = true;
// If the rethrow destination has a single branch predecessor,
// consider emitting the rethrow into it.
SILBasicBlock *predBB = *rethrowBB->pred_begin();
if (std::next(rethrowBB->pred_begin()) == rethrowBB->pred_end()) {
if (auto branch = dyn_cast<BranchInst>(predBB->getTerminator())) {
assert(branch->getArgs().size() == 1);
// Save the location and operand information from the branch,
// then destroy it.
throwLoc = branch->getLoc();
exn = branch->getArgs()[0];
predBB->erase(branch);
// Erase the rethrow block.
eraseBasicBlock(rethrowBB);
rethrowBB = predBB;
reposition = false;
}
}
// Reposition the rethrow block to the end of the postmatter section
// unless we're emitting into a single predecessor.
if (reposition) {
B.moveBlockTo(rethrowBB, F.end());
}
B.setInsertionPoint(rethrowBB);
Cleanups.emitCleanupsForReturn(ThrowDest.getCleanupLocation());
B.createThrow(throwLoc, exn);
ThrowDest = JumpDest::invalid();
}
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