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

include/llvm/LinkAllPasses.h

@@ -149,6 +149,7 @@ namespace {
       (void) llvm::createLintPass();
       (void) llvm::createSinkingPass();
       (void) llvm::createLowerAtomicPass();
+      (void) llvm::createValuePropagationPass();
 
       (void)new llvm::IntervalPartition();
       (void)new llvm::FindUsedTypes();

include/llvm/Transforms/Scalar.h

@@ -343,6 +343,12 @@ FunctionPass *createSinkingPass();
 //
 Pass *createLowerAtomicPass();
 
+//===----------------------------------------------------------------------===//
+//
+// ValuePropagation - Propagate CFG-derived value information
+//
+Pass *createValuePropagationPass();
+
 } // End llvm namespace
 
 #endif

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;
+}

test/Transforms/ValuePropagation/dg.exp

@@ -0,0 +1,3 @@
+load_lib llvm.exp
+
+RunLLVMTests [lsort [glob -nocomplain $srcdir/$subdir/*.ll]]

test/Transforms/ValuePropagation/phi.ll

@@ -0,0 +1,17 @@
+; RUN: opt < %s -value-propagation -S | FileCheck %s
+; PR2581
+
+; CHECK: @run
+define i32 @run(i1 %C) nounwind  {
+        br i1 %C, label %exit, label %body
+
+body:           ; preds = %0
+; CHECK-NOT: select
+        %A = select i1 %C, i32 10, i32 11               ; <i32> [#uses=1]
+; CHECK: ret i32 11
+        ret i32 %A
+
+exit:           ; preds = %0
+; CHECK: ret i32 10
+        ret i32 10
+}

test/Transforms/ValuePropagation/select.ll

@@ -0,0 +1,25 @@
+; RUN: opt < %s -value-propagation -S | FileCheck %s
+; PR4420
+
+declare i1 @ext()
+; CHECK: @foo
+define i1 @foo() {
+entry:
+        %cond = tail call i1 @ext()             ; <i1> [#uses=2]
+        br i1 %cond, label %bb1, label %bb2
+
+bb1:            ; preds = %entry
+        %cond2 = tail call i1 @ext()            ; <i1> [#uses=1]
+        br i1 %cond2, label %bb3, label %bb2
+
+bb2:            ; preds = %bb1, %entry
+; CHECK-NOT: phi i1
+        %cond_merge = phi i1 [ %cond, %entry ], [ false, %bb1 ]         ; <i1> [#uses=1]
+; CHECK: ret i1 false
+        ret i1 %cond_merge
+
+bb3:            ; preds = %bb1
+        %res = tail call i1 @ext()              ; <i1> [#uses=1]
+; CHECK: ret i1 %res
+        ret i1 %res
+}