[llvm-commits] CVS: llvm/lib/Transforms/IPO/IPConstantPropagation.cpp
Chris Lattner
lattner at cs.uiuc.edu
Thu Oct 23 11:53:02 PDT 2003
Changes in directory llvm/lib/Transforms/IPO:
IPConstantPropagation.cpp added (r1.1)
---
Log message:
Check in initial version of ipcp
---
Diffs of the changes: (+110 -0)
Index: llvm/lib/Transforms/IPO/IPConstantPropagation.cpp
diff -c /dev/null llvm/lib/Transforms/IPO/IPConstantPropagation.cpp:1.1
*** /dev/null Thu Oct 23 11:52:37 2003
--- llvm/lib/Transforms/IPO/IPConstantPropagation.cpp Thu Oct 23 11:52:27 2003
***************
*** 0 ****
--- 1,110 ----
+ //===-- IPConstantPropagation.cpp - Propagate constants through calls -----===//
+ //
+ // The LLVM Compiler Infrastructure
+ //
+ // This file was developed by the LLVM research group and is distributed under
+ // the University of Illinois Open Source License. See LICENSE.TXT for details.
+ //
+ //===----------------------------------------------------------------------===//
+ //
+ // This pass implements an _extremely_ simple interprocedural constant
+ // propagation pass. It could certainly be improved in many different ways,
+ // like using a worklist. This pass makes arguments dead, but does not remove
+ // them. The existing dead argument elimination pass should be run after this
+ // to clean up the mess.
+ //
+ //===----------------------------------------------------------------------===//
+
+ #include "llvm/Transforms/IPO.h"
+ #include "llvm/Module.h"
+ #include "llvm/Pass.h"
+ #include "llvm/Constants.h"
+ #include "llvm/Support/CallSite.h"
+ #include "Support/Statistic.h"
+
+ namespace {
+ Statistic<> NumArgumentsProped("ipconstprop",
+ "Number of args turned into constants");
+
+ /// IPCP - The interprocedural constant propagation pass
+ ///
+ struct IPCP : public Pass {
+ bool run(Module &M);
+ private:
+ bool processFunction(Function &F);
+ };
+ RegisterOpt<IPCP> X("ipconstprop", "Interprocedural constant propagation");
+ }
+
+ Pass *createIPConstantPropagationPass() { return new IPCP(); }
+
+ bool IPCP::run(Module &M) {
+ bool Changed = false;
+ for (Module::iterator I = M.begin(), E = M.end(); I != E; ++I)
+ if (!I->isExternal() && I->hasInternalLinkage())
+ Changed |= processFunction(*I);
+ return Changed;
+ }
+
+ /// processFunction - Look at all uses of the specified function. If all uses
+ /// are direct call sites, and all pass a particular constant in for an
+ /// argument, propagate that constant in as the argument.
+ ///
+ bool IPCP::processFunction(Function &F) {
+ if (F.aempty() || F.use_empty()) return false; // No arguments? Early exit.
+
+ std::vector<std::pair<Constant*, bool> > ArgumentConstants;
+ ArgumentConstants.resize(F.asize());
+
+ unsigned NumNonconstant = 0;
+
+ for (Value::use_iterator I = F.use_begin(), E = F.use_end(); I != E; ++I)
+ if (!isa<Instruction>(*I))
+ return false; // Used by a non-instruction, do not transform
+ else {
+ CallSite CS = CallSite::get(cast<Instruction>(*I));
+ if (CS.getInstruction() == 0 ||
+ CS.getCalledFunction() != &F)
+ return false; // Not a direct call site?
+
+ // Check out all of the potentially constant arguments
+ CallSite::arg_iterator AI = CS.arg_begin();
+ for (unsigned i = 0, e = ArgumentConstants.size(); i != e; ++i, ++AI) {
+ if (*AI == &F) return false; // Passes the function into itself
+
+ if (!ArgumentConstants[i].second) {
+ if (isa<Constant>(*AI) || isa<GlobalValue>(*AI)) {
+ Constant *C = dyn_cast<Constant>(*AI);
+ if (!C) C = ConstantPointerRef::get(cast<GlobalValue>(*AI));
+
+ if (!ArgumentConstants[i].first)
+ ArgumentConstants[i].first = C;
+ else if (ArgumentConstants[i].first != C) {
+ // Became non-constant
+ ArgumentConstants[i].second = true;
+ ++NumNonconstant;
+ if (NumNonconstant == ArgumentConstants.size()) return false;
+ }
+ } else {
+ // This is not a constant argument. Mark the argument as
+ // non-constant.
+ ArgumentConstants[i].second = true;
+ ++NumNonconstant;
+ if (NumNonconstant == ArgumentConstants.size()) return false;
+ }
+ }
+ }
+ }
+
+ // If we got to this point, there is a constant argument!
+ assert(NumNonconstant != ArgumentConstants.size());
+ Function::aiterator AI = F.abegin();
+ for (unsigned i = 0, e = ArgumentConstants.size(); i != e; ++i, ++AI)
+ // Do we have a constant argument!?
+ if (!ArgumentConstants[i].second) {
+ assert(ArgumentConstants[i].first && "Unknown constant value!");
+ AI->replaceAllUsesWith(ArgumentConstants[i].first);
+ ++NumArgumentsProped;
+ }
+ return true;
+ }
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