return GlobalSwapBenefits > 0;
}
+/// \brief Check that one use is in the same block as the definition and all
+/// other uses are in blocks dominated by a given block
+///
+/// \param DI Definition
+/// \param UI Use
+/// \param DB Block that must dominate all uses of \p DI outside
+/// the parent block. Note there can be a use of \p DI in \p DB.
+/// \return true when \p UI is the only use of \p DI in the parent block
+/// and all other uses of \p DI are in blocks dominated by \p DB.
+///
+bool InstCombiner::dominatesAllUses(const Instruction *DI,
+ const Instruction *UI,
+ const BasicBlock *DB) const {
+ assert(DI && DI->getParent() == UI->getParent() &&
+ "definition and use must be in the same block");
+ // DominatorTree available?
+ if (!DT)
+ return false;
+ for (const User *U : DI->users()) {
+ auto *Usr = cast<Instruction>(U);
+ if (Usr != UI && !DT->dominates(DB, Usr->getParent()))
+ return false;
+ }
+ return true;
+}
+
+///
+/// true when the instruction sequence within a block is select-cmp-br.
+///
+static bool isChainSelectCmpBranch(const SelectInst *SI) {
+ const BasicBlock *BB = SI->getParent();
+ if (!BB)
+ return false;
+ auto *BI = dyn_cast_or_null<BranchInst>(BB->getTerminator());
+ if (!BI || BI->getNumSuccessors() != 2)
+ return false;
+ auto *IC = dyn_cast<ICmpInst>(BI->getCondition());
+ if (!IC || (IC->getOperand(0) != SI && IC->getOperand(1) != SI))
+ return false;
+ return true;
+}
+
+///
+/// \brief True when a select result is replaced by one of its operands
+/// in select-icmp sequence. This will eventually result in the elimination
+/// of the select.
+///
+/// \param SI Select instruction
+/// \param Icmp Compare instruction
+/// \param CI1 'true' when first select operand is equal to RHSC of Icmp
+/// \param CI2 'true' when second select operand is equal to RHSC of Icmp
+///
+/// Notes:
+/// - The replacement is global and requires dominator information
+/// - The caller is responsible for the actual replacement
+///
+/// Example:
+///
+/// entry:
+/// %4 = select i1 %3, %C* %0, %C* null
+/// %5 = icmp eq %C* %4, null
+/// br i1 %5, label %9, label %7
+/// ...
+/// ; <label>:7 ; preds = %entry
+/// %8 = getelementptr inbounds %C* %4, i64 0, i32 0
+/// ...
+///
+/// can be transformed to
+///
+/// %5 = icmp eq %C* %0, null
+/// %6 = select i1 %3, i1 %5, i1 true
+/// br i1 %6, label %9, label %7
+/// ...
+/// ; <label>:7 ; preds = %entry
+/// %8 = getelementptr inbounds %C* %0, i64 0, i32 0 // replace by %0!
+///
+/// Similar when the first operand of the select is a constant or/and
+/// the compare is for not equal rather than equal.
+///
+/// FIXME: Currently the function considers equal compares only. It should be
+/// possbile to extend it to not equal compares also.
+///
+bool InstCombiner::replacedSelectWithOperand(SelectInst *SI,
+ const ICmpInst *Icmp,
+ const ConstantInt *CI1,
+ const ConstantInt *CI2) {
+ if (isChainSelectCmpBranch(SI) && Icmp->isEquality()) {
+ // Code sequence is select - icmp.[eq|ne] - br
+ unsigned ReplaceWithOpd = 0;
+ if (CI1 && !CI1->isZero())
+ // The first constant operand of the select and the RHS of
+ // the compare match, so try to substitute
+ // the select results with its second operand
+ // Example:
+ // %4 = select i1 %3, %C* null, %C* %0
+ // %5 = icmp eq %C* %4, null
+ // ==> could replace select with second operand
+ ReplaceWithOpd = 2;
+ else if (CI2 && !CI2->isZero())
+ // Similar when the second operand of the select is a constant
+ // Example:
+ // %4 = select i1 %3, %C* %0, %C* null
+ // %5 = icmp eq %C* %4, null
+ // ==> could replace select with first operand
+ ReplaceWithOpd = 1;
+ if (ReplaceWithOpd) {
+ // Replace select with operand on else path for EQ compares.
+ // Replace select with operand on then path for NE compares.
+ BasicBlock *Succ =
+ Icmp->getPredicate() == ICmpInst::ICMP_EQ
+ ? SI->getParent()->getTerminator()->getSuccessor(1)
+ : SI->getParent()->getTerminator()->getSuccessor(0);
+ if (InstCombiner::dominatesAllUses(SI, Icmp, Succ)) {
+ SI->replaceAllUsesWith(SI->getOperand(ReplaceWithOpd));
+ return true;
+ }
+ }
+ }
+ return false;
+}
+
Instruction *InstCombiner::visitICmpInst(ICmpInst &I) {
bool Changed = false;
Value *Op0 = I.getOperand(0), *Op1 = I.getOperand(1);
// fold to a constant (in which case the icmp is replaced with a select
// which will usually simplify) or this is the only user of the
// select (in which case we are trading a select+icmp for a simpler
- // select+icmp).
- if ((Op1 && Op2) || (LHSI->hasOneUse() && (Op1 || Op2))) {
+ // select+icmp) or all uses of the select can be replaced based on
+ // dominance information ("Global cases").
+ bool Transform = false;
+ if (Op1 && Op2)
+ Transform = true;
+ else if (Op1 || Op2) {
+ if (LHSI->hasOneUse())
+ Transform = true;
+ else
+ // Global cases
+ Transform = replacedSelectWithOperand(
+ cast<SelectInst>(LHSI), &I, dyn_cast_or_null<ConstantInt>(Op1),
+ dyn_cast_or_null<ConstantInt>(Op2));
+ }
+ if (Transform) {
if (!Op1)
Op1 = Builder->CreateICmp(I.getPredicate(), LHSI->getOperand(1),
RHSC, I.getName());
projects / oota-llvm.git / blobdiff