[llvm-commits] CVS: llvm/lib/Analysis/LoadValueNumbering.cpp
Chris Lattner
lattner at cs.uiuc.edu
Mon Mar 15 00:01:19 PST 2004
Changes in directory llvm/lib/Analysis:
LoadValueNumbering.cpp updated: 1.15 -> 1.16
---
Log message:
Implement CSE of call instructions in the most trivial case. This implements
GCSE/call_cse.ll
---
Diffs of the changes: (+139 -11)
Index: llvm/lib/Analysis/LoadValueNumbering.cpp
diff -u llvm/lib/Analysis/LoadValueNumbering.cpp:1.15 llvm/lib/Analysis/LoadValueNumbering.cpp:1.16
--- llvm/lib/Analysis/LoadValueNumbering.cpp:1.15 Thu Feb 5 11:20:00 2004
+++ llvm/lib/Analysis/LoadValueNumbering.cpp Sun Mar 14 23:44:59 2004
@@ -7,27 +7,31 @@
//
//===----------------------------------------------------------------------===//
//
-// This file implements a value numbering pass that value #'s load instructions.
-// To do this, it finds lexically identical load instructions, and uses alias
-// analysis to determine which loads are guaranteed to produce the same value.
+// This file implements a value numbering pass that value numbers load and call
+// instructions. To do this, it finds lexically identical load instructions,
+// and uses alias analysis to determine which loads are guaranteed to produce
+// the same value. To value number call instructions, it looks for calls to
+// functions that do not write to memory which do not have intervening
+// instructions that clobber the memory that is read from.
//
// This pass builds off of another value numbering pass to implement value
-// numbering for non-load instructions. It uses Alias Analysis so that it can
-// disambiguate the load instructions. The more powerful these base analyses
-// are, the more powerful the resultant analysis will be.
+// numbering for non-load and non-call instructions. It uses Alias Analysis so
+// that it can disambiguate the load instructions. The more powerful these base
+// analyses are, the more powerful the resultant value numbering will be.
//
//===----------------------------------------------------------------------===//
#include "llvm/Analysis/LoadValueNumbering.h"
+#include "llvm/Function.h"
+#include "llvm/iMemory.h"
+#include "llvm/iOther.h"
+#include "llvm/Pass.h"
+#include "llvm/Type.h"
#include "llvm/Analysis/ValueNumbering.h"
#include "llvm/Analysis/AliasAnalysis.h"
#include "llvm/Analysis/Dominators.h"
-#include "llvm/Target/TargetData.h"
-#include "llvm/Pass.h"
-#include "llvm/Type.h"
-#include "llvm/iMemory.h"
-#include "llvm/BasicBlock.h"
#include "llvm/Support/CFG.h"
+#include "llvm/Target/TargetData.h"
#include <set>
using namespace llvm;
@@ -50,6 +54,11 @@
///
virtual void getEqualNumberNodes(Value *V1,
std::vector<Value*> &RetVals) const;
+
+ /// getCallEqualNumberNodes - Given a call instruction, find other calls
+ /// that have the same value number.
+ void getCallEqualNumberNodes(CallInst *CI,
+ std::vector<Value*> &RetVals) const;
};
// Register this pass...
@@ -109,6 +118,122 @@
return true;
}
+/// getCallEqualNumberNodes - Given a call instruction, find other calls that
+/// have the same value number.
+void LoadVN::getCallEqualNumberNodes(CallInst *CI,
+ std::vector<Value*> &RetVals) const {
+ Function *CF = CI->getCalledFunction();
+ if (CF == 0) return; // Indirect call.
+ AliasAnalysis &AA = getAnalysis<AliasAnalysis>();
+ if (!AA.onlyReadsMemory(CF)) return; // Nothing we can do.
+
+ // Scan all of the arguments of the function, looking for one that is not
+ // global. In particular, we would prefer to have an argument or instruction
+ // operand to chase the def-use chains of.
+ Value *Op = CF;
+ for (unsigned i = 1, e = CI->getNumOperands(); i != e; ++i)
+ if (isa<Argument>(CI->getOperand(i)) ||
+ isa<Instruction>(CI->getOperand(i))) {
+ Op = CI->getOperand(i);
+ break;
+ }
+
+ // Identify all lexically identical calls in this function.
+ std::vector<CallInst*> IdenticalCalls;
+
+ Function *CIFunc = CI->getParent()->getParent();
+ for (Value::use_iterator UI = Op->use_begin(), E = Op->use_end(); UI != E;
+ ++UI)
+ if (CallInst *C = dyn_cast<CallInst>(*UI))
+ if (C->getNumOperands() == CI->getNumOperands() &&
+ C->getOperand(0) == CI->getOperand(0) &&
+ C->getParent()->getParent() == CIFunc && C != CI) {
+ bool AllOperandsEqual = true;
+ for (unsigned i = 1, e = CI->getNumOperands(); i != e; ++i)
+ if (C->getOperand(i) != CI->getOperand(i)) {
+ AllOperandsEqual = false;
+ break;
+ }
+
+ if (AllOperandsEqual)
+ IdenticalCalls.push_back(C);
+ }
+
+ if (IdenticalCalls.empty()) return;
+
+ // Eliminate duplicates, which could occur if we chose a value that is passed
+ // into a call site multiple times.
+ std::sort(IdenticalCalls.begin(), IdenticalCalls.end());
+ IdenticalCalls.erase(std::unique(IdenticalCalls.begin(),IdenticalCalls.end()),
+ IdenticalCalls.end());
+
+ // If the call reads memory, we must make sure that there are no stores
+ // between the calls in question.
+ //
+ // FIXME: This should use mod/ref information. What we really care about it
+ // whether an intervening instruction could modify memory that is read, not
+ // ANY memory.
+ //
+ if (!AA.doesNotAccessMemory(CF)) {
+ DominatorSet &DomSetInfo = getAnalysis<DominatorSet>();
+ BasicBlock *CIBB = CI->getParent();
+ for (unsigned i = 0; i != IdenticalCalls.size(); ++i) {
+ CallInst *C = IdenticalCalls[i];
+ bool CantEqual = false;
+
+ if (DomSetInfo.dominates(CIBB, C->getParent())) {
+ // FIXME: we currently only handle the case where both calls are in the
+ // same basic block.
+ if (CIBB != C->getParent()) {
+ CantEqual = true;
+ } else {
+ Instruction *First = CI, *Second = C;
+ if (!DomSetInfo.dominates(CI, C))
+ std::swap(First, Second);
+
+ // Scan the instructions between the calls, checking for stores or
+ // calls to dangerous functions.
+ BasicBlock::iterator I = First;
+ for (++First; I != BasicBlock::iterator(Second); ++I) {
+ if (isa<StoreInst>(I)) {
+ // FIXME: We could use mod/ref information to make this much
+ // better!
+ CantEqual = true;
+ break;
+ } else if (CallInst *CI = dyn_cast<CallInst>(I)) {
+ if (CI->getCalledFunction() == 0 ||
+ !AA.onlyReadsMemory(CI->getCalledFunction())) {
+ CantEqual = true;
+ break;
+ }
+ } else if (I->mayWriteToMemory()) {
+ CantEqual = true;
+ break;
+ }
+ }
+ }
+
+ } else if (DomSetInfo.dominates(C->getParent(), CIBB)) {
+ // FIXME: We could implement this, but we don't for now.
+ CantEqual = true;
+ } else {
+ // FIXME: if one doesn't dominate the other, we can't tell yet.
+ CantEqual = true;
+ }
+
+
+ if (CantEqual) {
+ // This call does not produce the same value as the one in the query.
+ std::swap(IdenticalCalls[i--], IdenticalCalls.back());
+ IdenticalCalls.pop_back();
+ }
+ }
+ }
+
+ // Any calls that are identical and not destroyed will produce equal values!
+ for (unsigned i = 0, e = IdenticalCalls.size(); i != e; ++i)
+ RetVals.push_back(IdenticalCalls[i]);
+}
// getEqualNumberNodes - Return nodes with the same value number as the
// specified Value. This fills in the argument vector with any equal values.
@@ -121,6 +246,9 @@
getAnalysis<AliasAnalysis>().getMustAliases(V, RetVals);
if (!isa<LoadInst>(V)) {
+ if (CallInst *CI = dyn_cast<CallInst>(V))
+ return getCallEqualNumberNodes(CI, RetVals);
+
// Not a load instruction? Just chain to the base value numbering
// implementation to satisfy the request...
assert(&getAnalysis<ValueNumbering>() != (ValueNumbering*)this &&
More information about the llvm-commits
mailing list