pranavk updated this revision to Diff 521114.
pranavk added a comment.
[AArch64][InstCombine] Bail out for bitselect instructions
Repository:
rG LLVM Github Monorepo
CHANGES SINCE LAST ACTION
https://reviews.llvm.org/D147266/new/
https://reviews.llvm.org/D147266
Files:
llvm/lib/Transforms/InstCombine/InstCombineVectorOps.cpp
Index: llvm/lib/Transforms/InstCombine/InstCombineVectorOps.cpp
===================================================================
--- llvm/lib/Transforms/InstCombine/InstCombineVectorOps.cpp
+++ llvm/lib/Transforms/InstCombine/InstCombineVectorOps.cpp
@@ -56,6 +56,29 @@
///
/// FIXME: It's possible to create more instructions than previously existed.
static bool cheapToScalarize(Value *V, Value *EI) {
+ // Pattern: or(and(a, mask), and(b, ~mask)) can be efficiently folded to
bitselect instructions
+ // where ~mask = xor mask, -1
+ if (isa<Instruction>(V)) {
+ Instruction *TI = cast<Instruction>(V);
+ if (TI->getOpcode() == Instruction::Or) {
+ Value *LHS = TI->getOperand(0);
+ Value *RHS = TI->getOperand(1);
+ Value *MaskValue = nullptr;
+ Value *MaskConst = nullptr;
+
+ if (match(LHS, m_And(m_Value(), m_Value(MaskValue))) &&
+ match(RHS, m_And(m_Value(), m_Xor(m_Specific(MaskValue),
m_Value(MaskConst))))) {
+ if (auto *CI = dyn_cast<ConstantDataVector>(MaskConst)) {
+ Constant *C = CI->getSplatValue();
+ if (C->isAllOnesValue()) {
+ llvm::outs() << "return false from cheap\n";
+ return false;
+ }
+ }
+ }
+ }
+ }
+
ConstantInt *CEI = dyn_cast<ConstantInt>(EI);
// If we can pick a scalar constant value out of a vector, that is free.
Index: llvm/lib/Transforms/InstCombine/InstCombineVectorOps.cpp
===================================================================
--- llvm/lib/Transforms/InstCombine/InstCombineVectorOps.cpp
+++ llvm/lib/Transforms/InstCombine/InstCombineVectorOps.cpp
@@ -56,6 +56,29 @@
///
/// FIXME: It's possible to create more instructions than previously existed.
static bool cheapToScalarize(Value *V, Value *EI) {
+ // Pattern: or(and(a, mask), and(b, ~mask)) can be efficiently folded to bitselect instructions
+ // where ~mask = xor mask, -1
+ if (isa<Instruction>(V)) {
+ Instruction *TI = cast<Instruction>(V);
+ if (TI->getOpcode() == Instruction::Or) {
+ Value *LHS = TI->getOperand(0);
+ Value *RHS = TI->getOperand(1);
+ Value *MaskValue = nullptr;
+ Value *MaskConst = nullptr;
+
+ if (match(LHS, m_And(m_Value(), m_Value(MaskValue))) &&
+ match(RHS, m_And(m_Value(), m_Xor(m_Specific(MaskValue), m_Value(MaskConst))))) {
+ if (auto *CI = dyn_cast<ConstantDataVector>(MaskConst)) {
+ Constant *C = CI->getSplatValue();
+ if (C->isAllOnesValue()) {
+ llvm::outs() << "return false from cheap\n";
+ return false;
+ }
+ }
+ }
+ }
+ }
+
ConstantInt *CEI = dyn_cast<ConstantInt>(EI);
// If we can pick a scalar constant value out of a vector, that is free.
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