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Enhance GVN to propagate simple conditionals. This fixes PR3921.

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git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@68172 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Owen Anderson 2009-04-01 01:20:45 +00:00
parent b0426e86af
commit f41fcbb60d
2 changed files with 90 additions and 10 deletions
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48
lib/Transforms/Scalar/GVN.cpp
View File

@ -121,6 +121,7 @@ namespace {
AliasAnalysis* AA;
MemoryDependenceAnalysis* MD;
DominatorTree* DT;
uint32_t true_vn, false_vn;
uint32_t nextValueNumber;
@ -138,7 +139,14 @@ namespace {
Expression create_expression(CallInst* C);
Expression create_expression(Constant* C);
public:
ValueTable() : nextValueNumber(1) { }
ValueTable() : nextValueNumber(1) {
true_vn = lookup_or_add(ConstantInt::getTrue());
false_vn = lookup_or_add(ConstantInt::getFalse());
}
uint32_t getTrueVN() { return true_vn; }
uint32_t getFalseVN() { return false_vn; }
uint32_t lookup_or_add(Value* V);
uint32_t lookup(Value* V) const;
void add(Value* V, uint32_t num);
@ -1294,9 +1302,27 @@ bool GVN::processInstruction(Instruction *I,
uint32_t nextNum = VN.getNextUnusedValueNumber();
unsigned num = VN.lookup_or_add(I);
if (BranchInst* BI = dyn_cast<BranchInst>(I)) {
localAvail[I->getParent()]->table.insert(std::make_pair(num, I));
if (!BI->isConditional() || isa<Constant>(BI->getCondition()))
return false;
Value* branchCond = BI->getCondition();
uint32_t condVN = VN.lookup_or_add(branchCond);
BasicBlock* trueSucc = BI->getSuccessor(0);
BasicBlock* falseSucc = BI->getSuccessor(1);
localAvail[trueSucc]->table.insert(std::make_pair(condVN,
ConstantInt::getTrue()));
localAvail[falseSucc]->table.insert(std::make_pair(condVN,
ConstantInt::getFalse()));
return false;
// Allocations are always uniquely numbered, so we can save time and memory
// by fast failing them.
if (isa<AllocationInst>(I) || isa<TerminatorInst>(I)) {
// by fast failing them.
} else if (isa<AllocationInst>(I) || isa<TerminatorInst>(I)) {
localAvail[I->getParent()]->table.insert(std::make_pair(num, I));
return false;
}
@ -1405,18 +1431,11 @@ bool GVN::runOnFunction(Function& F) {
bool GVN::processBlock(BasicBlock* BB) {
DomTreeNode* DTN = DT->getNode(BB);
// FIXME: Kill off toErase by doing erasing eagerly in a helper function (and
// incrementing BI before processing an instruction).
SmallVector<Instruction*, 8> toErase;
bool changed_function = false;
if (DTN->getIDom())
localAvail[BB] =
new ValueNumberScope(localAvail[DTN->getIDom()->getBlock()]);
else
localAvail[BB] = new ValueNumberScope(0);
for (BasicBlock::iterator BI = BB->begin(), BE = BB->end();
BI != BE;) {
changed_function |= processInstruction(BI, toErase);
@ -1607,6 +1626,15 @@ bool GVN::performPRE(Function& F) {
bool GVN::iterateOnFunction(Function &F) {
cleanupGlobalSets();
for (df_iterator<DomTreeNode*> DI = df_begin(DT->getRootNode()),
DE = df_end(DT->getRootNode()); DI != DE; ++DI) {
if (DI->getIDom())
localAvail[DI->getBlock()] =
new ValueNumberScope(localAvail[DI->getIDom()->getBlock()]);
else
localAvail[DI->getBlock()] = new ValueNumberScope(0);
}
// Top-down walk of the dominator tree
bool changed = false;
#if 0

52
test/Transforms/GVN/condprop.ll Normal file
View File

@ -0,0 +1,52 @@
; RUN: llvm-as < %s | opt -gvn | llvm-dis | grep {br i1 false}
@a = external global i32 ; <i32*> [#uses=7]
define i32 @foo() nounwind {
entry:
%0 = load i32* @a, align 4 ; <i32> [#uses=1]
%1 = icmp eq i32 %0, 4 ; <i1> [#uses=1]
br i1 %1, label %bb, label %bb1
bb: ; preds = %entry
br label %bb8
bb1: ; preds = %entry
%2 = load i32* @a, align 4 ; <i32> [#uses=1]
%3 = icmp eq i32 %2, 5 ; <i1> [#uses=1]
br i1 %3, label %bb2, label %bb3
bb2: ; preds = %bb1
br label %bb8
bb3: ; preds = %bb1
%4 = load i32* @a, align 4 ; <i32> [#uses=1]
%5 = icmp eq i32 %4, 4 ; <i1> [#uses=1]
br i1 %5, label %bb4, label %bb5
bb4: ; preds = %bb3
%6 = load i32* @a, align 4 ; <i32> [#uses=1]
%7 = add i32 %6, 5 ; <i32> [#uses=1]
br label %bb8
bb5: ; preds = %bb3
%8 = load i32* @a, align 4 ; <i32> [#uses=1]
%9 = icmp eq i32 %8, 5 ; <i1> [#uses=1]
br i1 %9, label %bb6, label %bb7
bb6: ; preds = %bb5
%10 = load i32* @a, align 4 ; <i32> [#uses=1]
%11 = add i32 %10, 4 ; <i32> [#uses=1]
br label %bb8
bb7: ; preds = %bb5
%12 = load i32* @a, align 4 ; <i32> [#uses=1]
br label %bb8
bb8: ; preds = %bb7, %bb6, %bb4, %bb2, %bb
%.0 = phi i32 [ %12, %bb7 ], [ %11, %bb6 ], [ %7, %bb4 ], [ 4, %bb2 ], [ 5, %bb ] ; <i32> [#uses=1]
br label %return
return: ; preds = %bb8
ret i32 %.0
}