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Revert "[JumpThreading] Unfold selects that depend on the same condition" 

This reverts commit ac54d0066c478a09c7cd28d15d0f9ff8af984afc.

llvm-svn: 286976
This commit is contained in:
Pablo Barrio 2016-11-15 15:42:23 +00:00
parent 5f782bb048
commit 4f80c93a2e
3 changed files with 40 additions and 126 deletions
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2
llvm/include/llvm/Transforms/Scalar/JumpThreading.h
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@ -129,8 +129,6 @@ private:
BasicBlock *NewBB, BasicBlock *SuccBB);
/// Check if the block has profile metadata for its outgoing edges.
bool doesBlockHaveProfileData(BasicBlock *BB);
SelectInst *getSelectFedByPhi(PHINode *PN);
void expandSelect(SelectInst *SI);
};
} // end namespace llvm

119
llvm/lib/Transforms/Scalar/JumpThreading.cpp
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@ -1963,100 +1963,61 @@ bool JumpThreadingPass::TryToUnfoldSelect(CmpInst *CondCmp, BasicBlock *BB) {
return false;
}
/// GetSelectFedByPhi - Look for PHI/Select in the same BB of the form
/// TryToUnfoldSelectInCurrBB - Look for PHI/Select in the same BB of the form
/// bb:
/// %p = phi [false, %bb1], [true, %bb2], [false, %bb3], [true, %bb4], ...
/// %s = select p, trueval, falseval
///
/// And return the select. Unfolding it into a branch structure later enables
/// And expand the select into a branch structure. This later enables
/// jump-threading over bb in this pass.
///
/// Using the similar approach of SimplifyCFG::FoldCondBranchOnPHI(), return
/// select if the associated PHI has at least one constant.
SelectInst *JumpThreadingPass::getSelectFedByPhi(PHINode *PN) {
unsigned NumPHIValues = PN->getNumIncomingValues();
if (NumPHIValues == 0 || !PN->hasOneUse())
return nullptr;
SelectInst *SI = dyn_cast<SelectInst>(PN->user_back());
BasicBlock *BB = PN->getParent();
if (!SI || SI->getParent() != BB)
return nullptr;
Value *Cond = SI->getCondition();
if (!Cond || Cond != PN || !Cond->getType()->isIntegerTy(1))
return nullptr;
for (unsigned i = 0; i != NumPHIValues; ++i) {
if (PN->getIncomingBlock(i) == BB)
return nullptr;
if (isa<ConstantInt>(PN->getIncomingValue(i)))
return SI;
}
return nullptr;
}
/// ExpandSelect - Expand a select into an if-then-else construct.
void JumpThreadingPass::expandSelect(SelectInst *SI) {
BasicBlock *BB = SI->getParent();
TerminatorInst *Term =
SplitBlockAndInsertIfThen(SI->getCondition(), SI, false);
PHINode *NewPN = PHINode::Create(SI->getType(), 2, "", SI);
NewPN->addIncoming(SI->getTrueValue(), Term->getParent());
NewPN->addIncoming(SI->getFalseValue(), BB);
SI->replaceAllUsesWith(NewPN);
SI->eraseFromParent();
}
/// TryToUnfoldSelectInCurrBB - Unfold selects that could be jump-threaded were
/// they if-then-elses. If the unfolded selects are not jump-threaded, it will
/// be folded again in the later optimizations.
/// Using the similar approach of SimplifyCFG::FoldCondBranchOnPHI(), unfold
/// select if the associated PHI has at least one constant. If the unfolded
/// select is not jump-threaded, it will be folded again in the later
/// optimizations.
bool JumpThreadingPass::TryToUnfoldSelectInCurrBB(BasicBlock *BB) {
// If threading this would thread across a loop header, don't thread the edge.
// See the comments above FindLoopHeaders for justifications and caveats.
if (LoopHeaders.count(BB))
return false;
bool Changed = false;
for (auto &I : *BB) {
// Look for a Phi/Select pair in the same basic block. The Phi feeds the
// condition of the Select and at least one of the incoming values is a
// constant.
PHINode *PN;
SelectInst *SI;
if ((PN = dyn_cast<PHINode>(&I)) && (SI = getSelectFedByPhi(PN))) {
expandSelect(SI);
Changed = true;
// Look for a Phi/Select pair in the same basic block. The Phi feeds the
// condition of the Select and at least one of the incoming values is a
// constant.
for (BasicBlock::iterator BI = BB->begin();
PHINode *PN = dyn_cast<PHINode>(BI); ++BI) {
unsigned NumPHIValues = PN->getNumIncomingValues();
if (NumPHIValues == 0 || !PN->hasOneUse())
continue;
SelectInst *SI = dyn_cast<SelectInst>(PN->user_back());
if (!SI || SI->getParent() != BB)
continue;
Value *Cond = SI->getCondition();
if (!Cond || Cond != PN || !Cond->getType()->isIntegerTy(1))
continue;
bool HasConst = false;
for (unsigned i = 0; i != NumPHIValues; ++i) {
if (PN->getIncomingBlock(i) == BB)
return false;
if (isa<ConstantInt>(PN->getIncomingValue(i)))
HasConst = true;
}
if (I.getType()->isIntegerTy(1)) {
SmallVector<SelectInst *, 4> Selects;
// Look for scalar booleans used in selects as conditions. If there are
// several selects that use the same boolean, they are candidates for jump
// threading and therefore we should unfold them.
for (Value *U : I.users())
if (auto *SI = dyn_cast<SelectInst>(U))
Selects.push_back(SI);
if (Selects.size() <= 1)
continue;
// Remove duplicates
std::sort(Selects.begin(), Selects.end());
auto NewEnd = std::unique(Selects.begin(), Selects.end());
Changed = true;
for (auto SI = Selects.begin(); SI != NewEnd; ++SI)
expandSelect(*SI);
if (HasConst) {
// Expand the select.
TerminatorInst *Term =
SplitBlockAndInsertIfThen(SI->getCondition(), SI, false);
PHINode *NewPN = PHINode::Create(SI->getType(), 2, "", SI);
NewPN->addIncoming(SI->getTrueValue(), Term->getParent());
NewPN->addIncoming(SI->getFalseValue(), BB);
SI->replaceAllUsesWith(NewPN);
SI->eraseFromParent();
return true;
}
}
return Changed;
return false;
}

45
llvm/test/Transforms/JumpThreading/unfold-selects-same-cond.ll
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@ -1,45 +0,0 @@
; RUN: opt < %s -jump-threading -instcombine -simplifycfg -S | FileCheck %s
; The three selects are jump-threaded so that instcombine can optimize, and
; simplifycfg should turn the result into a single select.
define i32 @f(i32 %a, i32 %b) {
; CHECK: select
; CHECK-NOT: select
entry:
%0 = and i32 %a, 1
%1 = and i32 %b, 1
%xor = xor i32 %1, %a
%shr32 = lshr i32 %a, 1
%cmp10 = icmp eq i32 %xor, 1
%2 = xor i32 %b, 12345
%b.addr.1 = select i1 %cmp10, i32 %2, i32 %b
%shr1633 = lshr i32 %b.addr.1, 1
%3 = or i32 %shr1633, 54321
%b.addr.2 = select i1 %cmp10, i32 %3, i32 %shr1633
%shr1634 = lshr i32 %b.addr.2, 2
%4 = or i32 %shr1634, 54320
%b.addr.3 = select i1 %cmp10, i32 %4, i32 %shr1634
ret i32 %b.addr.3
}
; Case where the condition is not only used as condition but also as the
; true or false value in at least one of the selects.
define i1 @g(i32 %a, i32 %b) {
; CHECK: select
; CHECK-NOT: select
entry:
%0 = and i32 %a, 1
%1 = and i32 %b, 1
%xor = xor i32 %1, %a
%shr32 = lshr i32 %a, 1
%cmp10 = icmp eq i32 %xor, 1
%2 = xor i32 %b, 12345
%b.addr.1 = select i1 %cmp10, i32 %2, i32 %b
%shr1633 = lshr i32 %b.addr.1, 1
%3 = or i32 %shr1633, 54321
%b.addr.2 = select i1 %cmp10, i32 %3, i32 %shr1633
%shr1634 = lshr i32 %b.addr.2, 2
%4 = icmp eq i32 %shr1634, 54320
%b.addr.3 = select i1 %cmp10, i1 %4, i1 %cmp10
ret i1 %b.addr.3
}