[llvmcommits] CVS: llvm/lib/Analysis/ScalarEvolution.cpp
Chris Lattner
lattner at cs.uiuc.edu
Sun Jun 20 01:31:02 PDT 2004
Changes in directory llvm/lib/Analysis:
ScalarEvolution.cpp updated: 1.18 > 1.19

Log message:
Do not sort SCEV objects by address: instead sort by complexity and group
by address. This prevents the resultant SCEV objects from depending on
where in memory other scev objects happen to live.

Diffs of the changes: (+60 18)
Index: llvm/lib/Analysis/ScalarEvolution.cpp
diff u llvm/lib/Analysis/ScalarEvolution.cpp:1.18 llvm/lib/Analysis/ScalarEvolution.cpp:1.19
 llvm/lib/Analysis/ScalarEvolution.cpp:1.18 Tue Apr 27 10:12:45 2004
+++ llvm/lib/Analysis/ScalarEvolution.cpp Sun Jun 20 01:23:15 2004
@@ 107,22 +107,6 @@
//======//
// Implementation of the SCEV class.
//
namespace {
 /// SCEVComplexityCompare  Return true if the complexity of the LHS is less
 /// than the complexity of the RHS. If the SCEVs have identical complexity,
 /// order them by their addresses. This comparator is used to canonicalize
 /// expressions.
 struct SCEVComplexityCompare {
 bool operator()(SCEV *LHS, SCEV *RHS) {
 if (LHS>getSCEVType() < RHS>getSCEVType())
 return true;
 if (LHS>getSCEVType() == RHS>getSCEVType())
 return LHS < RHS;
 return false;
 }
 };
}

SCEV::~SCEV() {}
void SCEV::dump() const {
print(std::cerr);
@@ 339,6 +323,64 @@
WriteAsOperand(OS, V, false);
}
+//======//
+// SCEV Utilities
+//======//
+
+namespace {
+ /// SCEVComplexityCompare  Return true if the complexity of the LHS is less
+ /// than the complexity of the RHS. This comparator is used to canonicalize
+ /// expressions.
+ struct SCEVComplexityCompare {
+ bool operator()(SCEV *LHS, SCEV *RHS) {
+ return LHS>getSCEVType() < RHS>getSCEVType();
+ }
+ };
+}
+
+/// GroupByComplexity  Given a list of SCEV objects, order them by their
+/// complexity, and group objects of the same complexity together by value.
+/// When this routine is finished, we know that any duplicates in the vector are
+/// consecutive and that complexity is monotonically increasing.
+///
+/// Note that we go take special precautions to ensure that we get determinstic
+/// results from this routine. In other words, we don't want the results of
+/// this to depend on where the addresses of various SCEV objects happened to
+/// land in memory.
+///
+static void GroupByComplexity(std::vector<SCEVHandle> &Ops) {
+ if (Ops.size() < 2) return; // Noop
+ if (Ops.size() == 2) {
+ // This is the common case, which also happens to be trivially simple.
+ // Special case it.
+ if (Ops[0]>getSCEVType() > Ops[1]>getSCEVType())
+ std::swap(Ops[0], Ops[1]);
+ return;
+ }
+
+ // Do the rough sort by complexity.
+ std::sort(Ops.begin(), Ops.end(), SCEVComplexityCompare());
+
+ // Now that we are sorted by complexity, group elements of the same
+ // complexity. Note that this is, at worst, N^2, but the vector is likely to
+ // be extremely short in practice. Note that we take this approach because we
+ // do not want to depend on the addresses of the objects we are grouping.
+ for (unsigned i = 0, e = Ops.size(); i != e1; ++i) {
+ SCEV *S = Ops[i];
+ unsigned Complexity = S>getSCEVType();
+
+ // If there are any objects of the same complexity and same value as this
+ // one, group them.
+ for (unsigned j = i+1; j != e && Ops[j]>getSCEVType() == Complexity; ++j) {
+ if (Ops[j] == S) { // Found a duplicate.
+ // Move it to immediately after i'th element.
+ std::swap(Ops[i+1], Ops[j]);
+ ++i; // no need to rescan it.
+ }
+ }
+ }
+}
+
//======//
@@ 509,7 +551,7 @@
if (Ops.size() == 1) return Ops[0];
// Sort by complexity, this groups all similar expression types together.
 std::sort(Ops.begin(), Ops.end(), SCEVComplexityCompare());
+ GroupByComplexity(Ops);
// If there are any constants, fold them together.
unsigned Idx = 0;
@@ 737,7 +779,7 @@
assert(!Ops.empty() && "Cannot get empty mul!");
// Sort by complexity, this groups all similar expression types together.
 std::sort(Ops.begin(), Ops.end(), SCEVComplexityCompare());
+ GroupByComplexity(Ops);
// If there are any constants, fold them together.
unsigned Idx = 0;
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