* Eliminate dead code that should have been removed in last revision
* Convert main constant propogation pass to be worklist driven instead of
iterative.
* -constprop pass no longer "constant propogates" terminator instructions
- CFG is now preserved!
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@2502 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Transforms/Scalar/ConstantProp.cpp b/lib/Transforms/Scalar/ConstantProp.cpp
index aa46f2b..b43f237 100644
--- a/lib/Transforms/Scalar/ConstantProp.cpp
+++ b/lib/Transforms/Scalar/ConstantProp.cpp
@@ -1,122 +1,43 @@
-//===- ConstantProp.cpp - Code to perform Constant Propogation ------------===//
+//===- ConstantProp.cpp - Code to perform Simple Constant Propogation -----===//
//
// This file implements constant propogation and merging:
//
// Specifically, this:
-// * Folds multiple identical constants in the constant pool together
-// Note that if one is named and the other is not, that the result gets the
-// original name.
-// * Converts instructions like "add int %1, %2" into a direct def of %3 in
-// the constant pool
-// * Converts conditional branches on a constant boolean value into direct
-// branches.
-// * Converts phi nodes with one incoming def to the incoming def directly
-// . Converts switch statements with one entry into a test & conditional
-// branch
-// . Converts switches on constant values into an unconditional branch.
+// * Converts instructions like "add int 1, 2" into 3
//
// Notice that:
// * This pass has a habit of making definitions be dead. It is a good idea
-// to to run a DCE pass sometime after running this pass.
+// to to run a DIE pass sometime after running this pass.
//
//===----------------------------------------------------------------------===//
#include "llvm/Transforms/Scalar/ConstantProp.h"
#include "llvm/ConstantHandling.h"
-#include "llvm/Module.h"
#include "llvm/Function.h"
#include "llvm/BasicBlock.h"
#include "llvm/iTerminators.h"
-#include "llvm/iPHINode.h"
-#include "llvm/iOther.h"
#include "llvm/Pass.h"
+#include "llvm/Support/InstIterator.h"
+#include <set>
-inline static bool
-ConstantFoldUnaryInst(BasicBlock *BB, BasicBlock::iterator &II,
- UnaryOperator *Op, Constant *D) {
- Constant *ReplaceWith = ConstantFoldUnaryInstruction(Op->getOpcode(), D);
+// FIXME: ConstantFoldInstruction & ConstantFoldTerminator should be moved out
+// to the Transformations library.
- if (!ReplaceWith) return false; // Nothing new to change...
+// ConstantFoldInstruction - If an instruction references constants, try to fold
+// them together...
+//
+bool doConstantPropogation(BasicBlock *BB, BasicBlock::iterator &II) {
+ Instruction *Inst = *II;
+ if (Constant *C = ConstantFoldInstruction(Inst)) {
+ // Replaces all of the uses of a variable with uses of the constant.
+ Inst->replaceAllUsesWith(C);
+
+ // Remove the instruction from the basic block...
+ delete BB->getInstList().remove(II);
+ return true;
+ }
- // Replaces all of the uses of a variable with uses of the constant.
- Op->replaceAllUsesWith(ReplaceWith);
-
- // Remove the operator from the list of definitions...
- Op->getParent()->getInstList().remove(II);
-
- // The new constant inherits the old name of the operator...
- if (Op->hasName())
- ReplaceWith->setName(Op->getName(), BB->getParent()->getSymbolTableSure());
-
- // Delete the operator now...
- delete Op;
- return true;
-}
-
-inline static bool
-ConstantFoldCast(BasicBlock *BB, BasicBlock::iterator &II,
- CastInst *CI, Constant *D) {
- Constant *ReplaceWith = ConstantFoldCastInstruction(D, CI->getType());
-
- if (!ReplaceWith) return false; // Nothing new to change...
-
- // Replaces all of the uses of a variable with uses of the constant.
- CI->replaceAllUsesWith(ReplaceWith);
-
- // Remove the cast from the list of definitions...
- CI->getParent()->getInstList().remove(II);
-
- // The new constant inherits the old name of the cast...
- if (CI->hasName())
- ReplaceWith->setName(CI->getName(), BB->getParent()->getSymbolTableSure());
-
- // Delete the cast now...
- delete CI;
- return true;
-}
-
-inline static bool
-ConstantFoldBinaryInst(BasicBlock *BB, BasicBlock::iterator &II,
- BinaryOperator *Op,
- Constant *D1, Constant *D2) {
- Constant *ReplaceWith = ConstantFoldBinaryInstruction(Op->getOpcode(), D1,D2);
- if (!ReplaceWith) return false; // Nothing new to change...
-
- // Replaces all of the uses of a variable with uses of the constant.
- Op->replaceAllUsesWith(ReplaceWith);
-
- // Remove the operator from the list of definitions...
- Op->getParent()->getInstList().remove(II);
-
- // The new constant inherits the old name of the operator...
- if (Op->hasName())
- ReplaceWith->setName(Op->getName(), BB->getParent()->getSymbolTableSure());
-
- // Delete the operator now...
- delete Op;
- return true;
-}
-
-inline static bool
-ConstantFoldShiftInst(BasicBlock *BB, BasicBlock::iterator &II,
- ShiftInst *Op,
- Constant *D1, Constant *D2) {
- Constant *ReplaceWith = ConstantFoldShiftInstruction(Op->getOpcode(), D1,D2);
- if (!ReplaceWith) return false; // Nothing new to change...
-
- // Replaces all of the uses of a variable with uses of the constant.
- Op->replaceAllUsesWith(ReplaceWith);
-
- // Remove the operator from the list of definitions...
- Op->getParent()->getInstList().remove(II);
-
- // The new constant inherits the old name of the operator...
- if (Op->hasName())
- ReplaceWith->setName(Op->getName(), BB->getParent()->getSymbolTableSure());
-
- // Delete the operator now...
- delete Op;
- return true;
+ return false;
}
// ConstantFoldTerminator - If a terminator instruction is predicated on a
@@ -174,60 +95,16 @@
return false;
}
-// ConstantFoldInstruction - If an instruction references constants, try to fold
-// them together...
-//
-bool doConstantPropogation(BasicBlock *BB, BasicBlock::iterator &II) {
- Instruction *Inst = *II;
- if (TerminatorInst *TInst = dyn_cast<TerminatorInst>(Inst)) {
- return ConstantFoldTerminator(BB, II, TInst);
- } else if (Constant *C = ConstantFoldInstruction(Inst)) {
- // Replaces all of the uses of a variable with uses of the constant.
- Inst->replaceAllUsesWith(C);
-
- // Remove the instruction from the basic block...
- delete BB->getInstList().remove(II);
- return true;
- }
-
- return false;
-}
-
-// DoConstPropPass - Propogate constants and do constant folding on instructions
-// this returns true if something was changed, false if nothing was changed.
-//
-static bool DoConstPropPass(Function *F) {
- bool SomethingChanged = false;
-
- for (Function::iterator BBI = F->begin(); BBI != F->end(); ++BBI) {
- BasicBlock *BB = *BBI;
- for (BasicBlock::iterator I = BB->begin(); I != BB->end(); )
- if (doConstantPropogation(BB, I))
- SomethingChanged = true;
- else
- ++I;
- }
- return SomethingChanged;
-}
namespace {
struct ConstantPropogation : public FunctionPass {
const char *getPassName() const { return "Simple Constant Propogation"; }
- inline bool runOnFunction(Function *F) {
- bool Modified = false;
-
- // Fold constants until we make no progress...
- while (DoConstPropPass(F)) Modified = true;
-
- return Modified;
- }
+ inline bool runOnFunction(Function *F);
virtual void getAnalysisUsage(AnalysisUsage &AU) const {
- // FIXME: This pass does not preserve the CFG because it folds terminator
- // instructions!
- //AU.preservesCFG();
+ AU.preservesCFG();
}
};
}
@@ -236,3 +113,30 @@
return new ConstantPropogation();
}
+
+bool ConstantPropogation::runOnFunction(Function *F) {
+ // Initialize the worklist to all of the instructions ready to process...
+ std::set<Instruction*> WorkList(inst_begin(F), inst_end(F));
+ bool Changed = false;
+
+ while (!WorkList.empty()) {
+ Instruction *I = *WorkList.begin();
+ WorkList.erase(WorkList.begin()); // Get an element from the worklist...
+
+ if (!I->use_empty()) // Don't muck with dead instructions...
+ if (Constant *C = ConstantFoldInstruction(I)) {
+ // Add all of the users of this instruction to the worklist, they might
+ // be constant propogatable now...
+ for (Value::use_iterator UI = I->use_begin(), UE = I->use_end();
+ UI != UE; ++UI)
+ WorkList.insert(cast<Instruction>(*UI));
+
+ // Replace all of the uses of a variable with uses of the constant.
+ I->replaceAllUsesWith(C);
+
+ // We made a change to the function...
+ Changed = true;
+ }
+ }
+ return Changed;
+}