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-rw-r--r--include/llvm/Analysis/Dominators.h15
-rw-r--r--lib/Transforms/Scalar/GVN.cpp95
-rw-r--r--lib/VMCore/Dominators.cpp25
-rw-r--r--test/Transforms/GVN/edge.ll60
4 files changed, 133 insertions, 62 deletions
diff --git a/include/llvm/Analysis/Dominators.h b/include/llvm/Analysis/Dominators.h
index 1289edd..a1cc196 100644
--- a/include/llvm/Analysis/Dominators.h
+++ b/include/llvm/Analysis/Dominators.h
@@ -705,7 +705,20 @@ DominatorTreeBase<NodeT>::properlyDominates(const NodeT *A, const NodeT *B) {
EXTERN_TEMPLATE_INSTANTIATION(class DominatorTreeBase<BasicBlock>);
-class BasicBlockEdge;
+class BasicBlockEdge {
+ const BasicBlock *Start;
+ const BasicBlock *End;
+public:
+ BasicBlockEdge(const BasicBlock *Start_, const BasicBlock *End_) :
+ Start(Start_), End(End_) { }
+ const BasicBlock *getStart() const {
+ return Start;
+ }
+ const BasicBlock *getEnd() const {
+ return End;
+ }
+ bool isSingleEdge() const;
+};
//===-------------------------------------
/// DominatorTree Class - Concrete subclass of DominatorTreeBase that is used to
diff --git a/lib/Transforms/Scalar/GVN.cpp b/lib/Transforms/Scalar/GVN.cpp
index 120175d..4822fd0 100644
--- a/lib/Transforms/Scalar/GVN.cpp
+++ b/lib/Transforms/Scalar/GVN.cpp
@@ -613,8 +613,8 @@ namespace {
void verifyRemoved(const Instruction *I) const;
bool splitCriticalEdges();
unsigned replaceAllDominatedUsesWith(Value *From, Value *To,
- const BasicBlock *Root);
- bool propagateEquality(Value *LHS, Value *RHS, const BasicBlock *Root);
+ const BasicBlockEdge &Root);
+ bool propagateEquality(Value *LHS, Value *RHS, const BasicBlockEdge &Root);
};
char GVN::ID = 0;
@@ -2004,22 +2004,13 @@ Value *GVN::findLeader(const BasicBlock *BB, uint32_t num) {
/// use is dominated by the given basic block. Returns the number of uses that
/// were replaced.
unsigned GVN::replaceAllDominatedUsesWith(Value *From, Value *To,
- const BasicBlock *Root) {
+ const BasicBlockEdge &Root) {
unsigned Count = 0;
for (Value::use_iterator UI = From->use_begin(), UE = From->use_end();
UI != UE; ) {
Use &U = (UI++).getUse();
- // If From occurs as a phi node operand then the use implicitly lives in the
- // corresponding incoming block. Otherwise it is the block containing the
- // user that must be dominated by Root.
- BasicBlock *UsingBlock;
- if (PHINode *PN = dyn_cast<PHINode>(U.getUser()))
- UsingBlock = PN->getIncomingBlock(U);
- else
- UsingBlock = cast<Instruction>(U.getUser())->getParent();
-
- if (DT->dominates(Root, UsingBlock)) {
+ if (DT->dominates(Root, U)) {
U.set(To);
++Count;
}
@@ -2027,13 +2018,34 @@ unsigned GVN::replaceAllDominatedUsesWith(Value *From, Value *To,
return Count;
}
+/// isOnlyReachableViaThisEdge - There is an edge from 'Src' to 'Dst'. Return
+/// true if every path from the entry block to 'Dst' passes via this edge. In
+/// particular 'Dst' must not be reachable via another edge from 'Src'.
+static bool isOnlyReachableViaThisEdge(const BasicBlockEdge &E,
+ DominatorTree *DT) {
+ // While in theory it is interesting to consider the case in which Dst has
+ // more than one predecessor, because Dst might be part of a loop which is
+ // only reachable from Src, in practice it is pointless since at the time
+ // GVN runs all such loops have preheaders, which means that Dst will have
+ // been changed to have only one predecessor, namely Src.
+ const BasicBlock *Pred = E.getEnd()->getSinglePredecessor();
+ const BasicBlock *Src = E.getStart();
+ assert((!Pred || Pred == Src) && "No edge between these basic blocks!");
+ (void)Src;
+ return Pred != 0;
+}
+
/// propagateEquality - The given values are known to be equal in every block
/// dominated by 'Root'. Exploit this, for example by replacing 'LHS' with
/// 'RHS' everywhere in the scope. Returns whether a change was made.
-bool GVN::propagateEquality(Value *LHS, Value *RHS, const BasicBlock *Root) {
+bool GVN::propagateEquality(Value *LHS, Value *RHS,
+ const BasicBlockEdge &Root) {
SmallVector<std::pair<Value*, Value*>, 4> Worklist;
Worklist.push_back(std::make_pair(LHS, RHS));
bool Changed = false;
+ // For speed, compute a conservative fast approximation to
+ // DT->dominates(Root, Root.getEnd());
+ bool RootDominatesEnd = isOnlyReachableViaThisEdge(Root, DT);
while (!Worklist.empty()) {
std::pair<Value*, Value*> Item = Worklist.pop_back_val();
@@ -2065,9 +2077,6 @@ bool GVN::propagateEquality(Value *LHS, Value *RHS, const BasicBlock *Root) {
LVN = RVN;
}
}
- assert((!isa<Instruction>(RHS) ||
- DT->properlyDominates(cast<Instruction>(RHS)->getParent(), Root)) &&
- "Instruction doesn't dominate scope!");
// If value numbering later sees that an instruction in the scope is equal
// to 'LHS' then ensure it will be turned into 'RHS'. In order to preserve
@@ -2076,8 +2085,10 @@ bool GVN::propagateEquality(Value *LHS, Value *RHS, const BasicBlock *Root) {
// if RHS is an instruction (if an instruction in the scope is morphed into
// LHS then it will be turned into RHS by the next GVN iteration anyway, so
// using the leader table is about compiling faster, not optimizing better).
- if (!isa<Instruction>(RHS))
- addToLeaderTable(LVN, RHS, Root);
+ // The leader table only tracks basic blocks, not edges. Only add to if we
+ // have the simple case where the edge dominates the end.
+ if (RootDominatesEnd && !isa<Instruction>(RHS))
+ addToLeaderTable(LVN, RHS, Root.getEnd());
// Replace all occurrences of 'LHS' with 'RHS' everywhere in the scope. As
// LHS always has at least one use that is not dominated by Root, this will
@@ -2136,7 +2147,7 @@ bool GVN::propagateEquality(Value *LHS, Value *RHS, const BasicBlock *Root) {
// If the number we were assigned was brand new then there is no point in
// looking for an instruction realizing it: there cannot be one!
if (Num < NextNum) {
- Value *NotCmp = findLeader(Root, Num);
+ Value *NotCmp = findLeader(Root.getEnd(), Num);
if (NotCmp && isa<Instruction>(NotCmp)) {
unsigned NumReplacements =
replaceAllDominatedUsesWith(NotCmp, NotVal, Root);
@@ -2146,7 +2157,10 @@ bool GVN::propagateEquality(Value *LHS, Value *RHS, const BasicBlock *Root) {
}
// Ensure that any instruction in scope that gets the "A < B" value number
// is replaced with false.
- addToLeaderTable(Num, NotVal, Root);
+ // The leader table only tracks basic blocks, not edges. Only add to if we
+ // have the simple case where the edge dominates the end.
+ if (RootDominatesEnd)
+ addToLeaderTable(Num, NotVal, Root.getEnd());
continue;
}
@@ -2155,22 +2169,6 @@ bool GVN::propagateEquality(Value *LHS, Value *RHS, const BasicBlock *Root) {
return Changed;
}
-/// isOnlyReachableViaThisEdge - There is an edge from 'Src' to 'Dst'. Return
-/// true if every path from the entry block to 'Dst' passes via this edge. In
-/// particular 'Dst' must not be reachable via another edge from 'Src'.
-static bool isOnlyReachableViaThisEdge(BasicBlock *Src, BasicBlock *Dst,
- DominatorTree *DT) {
- // While in theory it is interesting to consider the case in which Dst has
- // more than one predecessor, because Dst might be part of a loop which is
- // only reachable from Src, in practice it is pointless since at the time
- // GVN runs all such loops have preheaders, which means that Dst will have
- // been changed to have only one predecessor, namely Src.
- BasicBlock *Pred = Dst->getSinglePredecessor();
- assert((!Pred || Pred == Src) && "No edge between these basic blocks!");
- (void)Src;
- return Pred != 0;
-}
-
/// processInstruction - When calculating availability, handle an instruction
/// by inserting it into the appropriate sets
bool GVN::processInstruction(Instruction *I) {
@@ -2210,18 +2208,20 @@ bool GVN::processInstruction(Instruction *I) {
BasicBlock *TrueSucc = BI->getSuccessor(0);
BasicBlock *FalseSucc = BI->getSuccessor(1);
+ // Avoid multiple edges early.
+ if (TrueSucc == FalseSucc)
+ return false;
+
BasicBlock *Parent = BI->getParent();
bool Changed = false;
- if (isOnlyReachableViaThisEdge(Parent, TrueSucc, DT))
- Changed |= propagateEquality(BranchCond,
- ConstantInt::getTrue(TrueSucc->getContext()),
- TrueSucc);
+ Value *TrueVal = ConstantInt::getTrue(TrueSucc->getContext());
+ BasicBlockEdge TrueE(Parent, TrueSucc);
+ Changed |= propagateEquality(BranchCond, TrueVal, TrueE);
- if (isOnlyReachableViaThisEdge(Parent, FalseSucc, DT))
- Changed |= propagateEquality(BranchCond,
- ConstantInt::getFalse(FalseSucc->getContext()),
- FalseSucc);
+ Value *FalseVal = ConstantInt::getFalse(FalseSucc->getContext());
+ BasicBlockEdge FalseE(Parent, FalseSucc);
+ Changed |= propagateEquality(BranchCond, FalseVal, FalseE);
return Changed;
}
@@ -2234,8 +2234,9 @@ bool GVN::processInstruction(Instruction *I) {
for (SwitchInst::CaseIt i = SI->case_begin(), e = SI->case_end();
i != e; ++i) {
BasicBlock *Dst = i.getCaseSuccessor();
- if (isOnlyReachableViaThisEdge(Parent, Dst, DT))
- Changed |= propagateEquality(SwitchCond, i.getCaseValue(), Dst);
+ BasicBlockEdge E(Parent, Dst);
+ if (E.isSingleEdge())
+ Changed |= propagateEquality(SwitchCond, i.getCaseValue(), E);
}
return Changed;
}
diff --git a/lib/VMCore/Dominators.cpp b/lib/VMCore/Dominators.cpp
index 682d928..60bdeac 100644
--- a/lib/VMCore/Dominators.cpp
+++ b/lib/VMCore/Dominators.cpp
@@ -39,20 +39,17 @@ static cl::opt<bool,true>
VerifyDomInfoX("verify-dom-info", cl::location(VerifyDomInfo),
cl::desc("Verify dominator info (time consuming)"));
-namespace llvm {
- class BasicBlockEdge {
- const BasicBlock *Start;
- const BasicBlock *End;
- public:
- BasicBlockEdge(const BasicBlock *Start_, const BasicBlock *End_) :
- Start(Start_), End(End_) { }
- const BasicBlock *getStart() const {
- return Start;
- }
- const BasicBlock *getEnd() const {
- return End;
- }
- };
+bool BasicBlockEdge::isSingleEdge() const {
+ const TerminatorInst *TI = Start->getTerminator();
+ unsigned NumEdgesToEnd = 0;
+ for (unsigned int i = 0, n = TI->getNumSuccessors(); i < n; ++i) {
+ if (TI->getSuccessor(i) == End)
+ ++NumEdgesToEnd;
+ if (NumEdgesToEnd >= 2)
+ return false;
+ }
+ assert(NumEdgesToEnd == 1);
+ return true;
}
//===----------------------------------------------------------------------===//
diff --git a/test/Transforms/GVN/edge.ll b/test/Transforms/GVN/edge.ll
new file mode 100644
index 0000000..32392f3
--- /dev/null
+++ b/test/Transforms/GVN/edge.ll
@@ -0,0 +1,60 @@
+; RUN: opt %s -gvn -S -o - | FileCheck %s
+
+define i32 @f1(i32 %x) {
+ ; CHECK: define i32 @f1(
+bb0:
+ %cmp = icmp eq i32 %x, 0
+ br i1 %cmp, label %bb2, label %bb1
+bb1:
+ br label %bb2
+bb2:
+ %cond = phi i32 [ %x, %bb0 ], [ 0, %bb1 ]
+ %foo = add i32 %cond, %x
+ ret i32 %foo
+ ; CHECK: bb2:
+ ; CHECK: ret i32 %x
+}
+
+define i32 @f2(i32 %x) {
+ ; CHECK: define i32 @f2(
+bb0:
+ %cmp = icmp ne i32 %x, 0
+ br i1 %cmp, label %bb1, label %bb2
+bb1:
+ br label %bb2
+bb2:
+ %cond = phi i32 [ %x, %bb0 ], [ 0, %bb1 ]
+ %foo = add i32 %cond, %x
+ ret i32 %foo
+ ; CHECK: bb2:
+ ; CHECK: ret i32 %x
+}
+
+define i32 @f3(i32 %x) {
+ ; CHECK: define i32 @f3(
+bb0:
+ switch i32 %x, label %bb1 [ i32 0, label %bb2]
+bb1:
+ br label %bb2
+bb2:
+ %cond = phi i32 [ %x, %bb0 ], [ 0, %bb1 ]
+ %foo = add i32 %cond, %x
+ ret i32 %foo
+ ; CHECK: bb2:
+ ; CHECK: ret i32 %x
+}
+
+declare void @g(i1)
+define void @f4(i8 * %x) {
+; CHECK: define void @f4(
+bb0:
+ %y = icmp eq i8* null, %x
+ br i1 %y, label %bb2, label %bb1
+bb1:
+ br label %bb2
+bb2:
+ %zed = icmp eq i8* null, %x
+ call void @g(i1 %zed)
+; CHECK: call void @g(i1 %y)
+ ret void
+}
generated by cgit v1.1 at 2025-01-08 18:46:48 +0000