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[JumpThreading] Add a pattern to TryToUnfoldSelectInCurrBB() 

Add the following pattern to TryToUnfoldSelectInCurrBB()

bb:
   %p = phi [0, %bb1], [1, %bb2], [0, %bb3], [1, %bb4], ...
   %c = cmp %p, 0
   %s = select %c, trueval, falseval

The Select in the above pattern will be unfolded and then jump-threaded. The
current implementation does not allow CMP in the middle of PHI and Select.

Differential Revision: https://reviews.llvm.org/D34762

llvm-svn: 308050
This commit is contained in:
Haicheng Wu 2017-07-14 19:16:47 +00:00
parent 302a9d41c6
commit 476adcca6b
2 changed files with 126 additions and 33 deletions
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82
llvm/lib/Transforms/Scalar/JumpThreading.cpp
View File

@ -2168,11 +2168,19 @@ bool JumpThreadingPass::TryToUnfoldSelect(CmpInst *CondCmp, BasicBlock *BB) {
return false;
}
/// TryToUnfoldSelectInCurrBB - Look for PHI/Select in the same BB of the form
/// TryToUnfoldSelectInCurrBB - Look for PHI/Select or PHI/CMP/Select in the
/// same BB in the form
/// bb:
/// %p = phi [false, %bb1], [true, %bb2], [false, %bb3], [true, %bb4], ...
/// %s = select p, trueval, falseval
/// %s = select %p, trueval, falseval
///
/// or
///
/// bb:
/// %p = phi [0, %bb1], [1, %bb2], [0, %bb3], [1, %bb4], ...
/// %c = cmp %p, 0
/// %s = select %c, trueval, falseval
//
/// And expand the select into a branch structure. This later enables
/// jump-threading over bb in this pass.
///
@ -2186,44 +2194,54 @@ bool JumpThreadingPass::TryToUnfoldSelectInCurrBB(BasicBlock *BB) {
if (LoopHeaders.count(BB))
return false;
// 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())
// Look for a Phi having at least one constant incoming value.
if (llvm::all_of(PN->incoming_values(),
[](Value *V) { return !isa<ConstantInt>(V); }))
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)
auto isUnfoldCandidate = [BB](SelectInst *SI, Value *V) {
// Check if SI is in BB and use V as condition.
if (SI->getParent() != BB)
return false;
if (isa<ConstantInt>(PN->getIncomingValue(i)))
HasConst = true;
Value *Cond = SI->getCondition();
return (Cond && Cond == V && Cond->getType()->isIntegerTy(1));
};
SelectInst *SI = nullptr;
for (Use &U : PN->uses()) {
if (ICmpInst *Cmp = dyn_cast<ICmpInst>(U.getUser())) {
// Look for a ICmp in BB that compares PN with a constant and is the
// condition of a Select.
if (Cmp->getParent() == BB && Cmp->hasOneUse() &&
isa<ConstantInt>(Cmp->getOperand(1 - U.getOperandNo())))
if (SelectInst *SelectI = dyn_cast<SelectInst>(Cmp->user_back()))
if (isUnfoldCandidate(SelectI, Cmp->use_begin()->get())) {
SI = SelectI;
break;
}
} else if (SelectInst *SelectI = dyn_cast<SelectInst>(U.getUser())) {
// Look for a Select in BB that uses PN as condtion.
if (isUnfoldCandidate(SelectI, U.get())) {
SI = SelectI;
break;
}
}
}
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;
}
if (!SI)
continue;
// 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 false;
}

77
llvm/test/Transforms/JumpThreading/select.ll
View File

@ -280,10 +280,85 @@ cond.false.15.i: ; preds = %cond.false.10.i
ret i32 %j.add3
; CHECK-LABEL: @unfold3
; CHECK: br i1 %cmp.i, label %.exit.thread2, label %cond.false.i
; CHECK: br i1 %cmp.i, label %.exit.thread2, label %cond.false.i
; CHECK: br i1 %cmp4.i, label %.exit.thread, label %cond.false.6.i
; CHECK: br i1 %cmp8.i, label %.exit.thread2, label %cond.false.10.i
; CHECK: br i1 %cmp13.i, label %.exit.thread, label %.exit
; CHECK: br i1 %phitmp, label %.exit.thread, label %.exit.thread2
; CHECK: br label %.exit.thread2
}
define i32 @unfold4(i32 %u, i32 %v, i32 %w, i32 %x, i32 %y, i32 %z, i32 %j) nounwind {
entry:
%add3 = add nsw i32 %j, 2
%cmp.i = icmp slt i32 %u, %v
br i1 %cmp.i, label %.exit, label %cond.false.i
cond.false.i: ; preds = %entry
%cmp4.i = icmp sgt i32 %u, %v
br i1 %cmp4.i, label %.exit, label %cond.false.6.i
cond.false.6.i: ; preds = %cond.false.i
%cmp8.i = icmp slt i32 %w, %x
br i1 %cmp8.i, label %.exit, label %cond.false.10.i
cond.false.10.i: ; preds = %cond.false.6.i
%cmp13.i = icmp sgt i32 %w, %x
br i1 %cmp13.i, label %.exit, label %cond.false.15.i
cond.false.15.i: ; preds = %cond.false.10.i
%cmp19.i = icmp sge i32 %y, %z
%conv = zext i1 %cmp19.i to i32
br label %.exit
.exit: ; preds = %entry, %cond.false.i, %cond.false.6.i, %cond.false.10.i, %cond.false.15.i
%cond23.i = phi i32 [ 1, %entry ], [ 0, %cond.false.i ], [ 1, %cond.false.6.i ], [ %conv, %cond.false.15.i ], [ 0, %cond.false.10.i ]
%lnot.i18 = icmp eq i32 %cond23.i, 1
%j.add3 = select i1 %lnot.i18, i32 %j, i32 %add3
ret i32 %j.add3
; CHECK-LABEL: @unfold4
; CHECK: br i1 %cmp.i, label %.exit.thread, label %cond.false.i
; CHECK: br i1 %cmp4.i, label %.exit.thread3, label %cond.false.6.i
; CHECK: br i1 %cmp8.i, label %.exit.thread, label %cond.false.10.i
; CHECK: br i1 %cmp13.i, label %.exit.thread3, label %.exit
; CHECK: br i1 %lnot.i18, label %.exit.thread, label %.exit.thread3
; CHECK: br label %.exit.thread3
}
define i32 @unfold5(i32 %u, i32 %v, i32 %w, i32 %x, i32 %y, i32 %z, i32 %j) nounwind {
entry:
%add3 = add nsw i32 %j, 2
%cmp.i = icmp slt i32 %u, %v
br i1 %cmp.i, label %.exit, label %cond.false.i
cond.false.i: ; preds = %entry
%cmp4.i = icmp sgt i32 %u, %v
br i1 %cmp4.i, label %.exit, label %cond.false.6.i
cond.false.6.i: ; preds = %cond.false.i
%cmp8.i = icmp slt i32 %w, %x
br i1 %cmp8.i, label %.exit, label %cond.false.10.i
cond.false.10.i: ; preds = %cond.false.6.i
%cmp13.i = icmp sgt i32 %w, %x
br i1 %cmp13.i, label %.exit, label %cond.false.15.i
cond.false.15.i: ; preds = %cond.false.10.i
%cmp19.i = icmp sge i32 %y, %z
%conv = zext i1 %cmp19.i to i32
br label %.exit
.exit: ; preds = %entry, %cond.false.i, %cond.false.6.i, %cond.false.10.i, %cond.false.15.i
%cond23.i = phi i32 [ 2, %entry ], [ 3, %cond.false.i ], [ 1, %cond.false.6.i ], [ %conv, %cond.false.15.i ], [ 7, %cond.false.10.i ]
%lnot.i18 = icmp sgt i32 %cond23.i, 5
%j.add3 = select i1 %lnot.i18, i32 %j, i32 %cond23.i
ret i32 %j.add3
; CHECK-LABEL: @unfold5
; CHECK: br i1 %cmp.i, label %.exit, label %cond.false.i
; CHECK: br i1 %cmp4.i, label %.exit, label %cond.false.6.i
; CHECK: br i1 %cmp8.i, label %.exit, label %cond.false.10.i
; CHECK: br i1 %cmp13.i, label %.exit, label %cond.false.15.i
; CHECK: br label %.exit
}