Add a prototype of a new peephole optimizing pass that uses LazyValue info to simplify PHIs and select's.
This pass addresses the missed optimizations from PR2581 and PR4420.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@112325 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Transforms/Scalar/ValuePropagation.cpp b/lib/Transforms/Scalar/ValuePropagation.cpp
new file mode 100644
index 0000000..c1384bb
--- /dev/null
+++ b/lib/Transforms/Scalar/ValuePropagation.cpp
@@ -0,0 +1,113 @@
+//===- ValuePropagation.cpp - Propagate information derived control flow --===//
+//
+// The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This file implements the Value Propagation pass.
+//
+//===----------------------------------------------------------------------===//
+
+#define DEBUG_TYPE "value-propagation"
+#include "llvm/Transforms/Scalar.h"
+#include "llvm/Function.h"
+#include "llvm/Instructions.h"
+#include "llvm/Pass.h"
+#include "llvm/Analysis/LazyValueInfo.h"
+#include "llvm/Transforms/Utils/Local.h"
+using namespace llvm;
+
+namespace {
+ class ValuePropagation : public FunctionPass {
+ LazyValueInfo *LVI;
+
+ bool processSelect(SelectInst *SI);
+ bool processPHI(PHINode *P);
+
+ public:
+ static char ID;
+ ValuePropagation(): FunctionPass(ID) { }
+
+ bool runOnFunction(Function &F);
+
+ virtual void getAnalysisUsage(AnalysisUsage &AU) const {
+ AU.addRequired<LazyValueInfo>();
+ }
+ };
+}
+
+char ValuePropagation::ID = 0;
+INITIALIZE_PASS(ValuePropagation, "value-propagation",
+ "Value Propagation", false, false);
+
+// Public interface to the Value Propagation pass
+Pass *llvm::createValuePropagationPass() {
+ return new ValuePropagation();
+}
+
+bool ValuePropagation::processSelect(SelectInst *S) {
+ Constant *C = LVI->getConstant(S->getOperand(0), S->getParent());
+ if (!C) return false;
+
+ ConstantInt *CI = dyn_cast<ConstantInt>(C);
+ if (!CI) return false;
+
+ if (CI->isZero()) {
+ S->replaceAllUsesWith(S->getOperand(2));
+ S->eraseFromParent();
+ } else if (CI->isOne()) {
+ S->replaceAllUsesWith(S->getOperand(1));
+ S->eraseFromParent();
+ } else {
+ assert(0 && "Select on constant is neither 0 nor 1?");
+ }
+
+ return true;
+}
+
+bool ValuePropagation::processPHI(PHINode *P) {
+ bool changed = false;
+
+ BasicBlock *BB = P->getParent();
+ for (unsigned i = 0; i < P->getNumIncomingValues(); ++i) {
+ Constant *C = LVI->getConstantOnEdge(P->getIncomingValue(i),
+ P->getIncomingBlock(i),
+ BB);
+ if (!C || C == P->getIncomingValue(i)) continue;
+
+ P->setIncomingValue(i, C);
+ changed = true;
+ }
+
+ if (Value *ConstVal = P->hasConstantValue()) {
+ P->replaceAllUsesWith(ConstVal);
+ P->eraseFromParent();
+ changed = true;
+ }
+
+ return changed;
+}
+
+bool ValuePropagation::runOnFunction(Function &F) {
+ LVI = &getAnalysis<LazyValueInfo>();
+
+ bool changed = false;
+
+ for (Function::iterator FI = F.begin(), FE = F.end(); FI != FE; ++FI)
+ for (BasicBlock::iterator BI = FI->begin(), BE = FI->end(); BI != BE; ) {
+ Instruction *II = BI++;
+ if (SelectInst *SI = dyn_cast<SelectInst>(II))
+ changed |= processSelect(SI);
+ else if (PHINode *P = dyn_cast<PHINode>(II))
+ changed |= processPHI(P);
+ }
+
+ if (changed)
+ for (Function::iterator FI = F.begin(), FE = F.end(); FI != FE; ++FI)
+ SimplifyInstructionsInBlock(FI);
+
+ return changed;
+}
\ No newline at end of file