[llvm] r295582 - NewGVN: Make ranking prefer undef to constants. Fix direction of
Daniel Berlin via llvm-commits
llvm-commits at lists.llvm.org
Sat Feb 18 15:06:48 PST 2017
Author: dannyb
Date: Sat Feb 18 17:06:47 2017
New Revision: 295582
URL: http://llvm.org/viewvc/llvm-project?rev=295582&view=rev
Log:
NewGVN: Make ranking prefer undef to constants. Fix direction of
shouldSwapOperands to be correct.
Modified:
llvm/trunk/lib/Transforms/Scalar/NewGVN.cpp
Modified: llvm/trunk/lib/Transforms/Scalar/NewGVN.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Scalar/NewGVN.cpp?rev=295582&r1=295581&r2=295582&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/Scalar/NewGVN.cpp (original)
+++ llvm/trunk/lib/Transforms/Scalar/NewGVN.cpp Sat Feb 18 17:06:47 2017
@@ -2402,16 +2402,19 @@ bool NewGVN::eliminateInstructions(Funct
// we will simplify an operation with all constants so that it doesn't matter
// what order they appear in.
unsigned int NewGVN::getRank(const Value *V) const {
- if (isa<Constant>(V))
+ // Prefer undef to anything else
+ if (isa<UndefValue>(V))
return 0;
+ if (isa<Constant>(V))
+ return 1;
else if (auto *A = dyn_cast<Argument>(V))
- return 1 + A->getArgNo();
+ return 2 + A->getArgNo();
- // Need to shift the instruction DFS by number of arguments + 2 to account for
+ // Need to shift the instruction DFS by number of arguments + 3 to account for
// the constant and argument ranking above.
unsigned Result = InstrDFS.lookup(V);
if (Result > 0)
- return 2 + NumFuncArgs + Result;
+ return 3 + NumFuncArgs + Result;
// Unreachable or something else, just return a really large number.
return ~0;
}
@@ -2421,8 +2424,6 @@ unsigned int NewGVN::getRank(const Value
bool NewGVN::shouldSwapOperands(const Value *A, const Value *B) const {
// Because we only care about a total ordering, and don't rewrite expressions
// in this order, we order by rank, which will give a strict weak ordering to
- // everything but constants, and then we order by pointer address. This is
- // not deterministic for constants, but it should not matter because any
- // operation with only constants will be folded (except, usually, for undef).
- return std::make_pair(getRank(B), B) > std::make_pair(getRank(A), A);
+ // everything but constants, and then we order by pointer address.
+ return std::make_pair(getRank(A), A) > std::make_pair(getRank(B), B);
}
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