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author | Duncan Sands <baldrick@free.fr> | 2012-02-29 11:12:03 +0000 |
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committer | Duncan Sands <baldrick@free.fr> | 2012-02-29 11:12:03 +0000 |
commit | 2b4f4910458f9bfd15315444ed47b4f41473a93d (patch) | |
tree | 84191d96ccfd0245b9139d796b740ca4cb171d20 /lib/Transforms | |
parent | 84a1d2371c026490f8dc6de93fd63802bfc512eb (diff) | |
download | external_llvm-2b4f4910458f9bfd15315444ed47b4f41473a93d.zip external_llvm-2b4f4910458f9bfd15315444ed47b4f41473a93d.tar.gz external_llvm-2b4f4910458f9bfd15315444ed47b4f41473a93d.tar.bz2 |
Have GVN also do condition propagation when the right-hand side is not
a constant. This fixes PR1768.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@151713 91177308-0d34-0410-b5e6-96231b3b80d8
Diffstat (limited to 'lib/Transforms')
-rw-r--r-- | lib/Transforms/Scalar/GVN.cpp | 31 |
1 files changed, 20 insertions, 11 deletions
diff --git a/lib/Transforms/Scalar/GVN.cpp b/lib/Transforms/Scalar/GVN.cpp index 702d1d7..37e970b 100644 --- a/lib/Transforms/Scalar/GVN.cpp +++ b/lib/Transforms/Scalar/GVN.cpp @@ -1972,21 +1972,30 @@ bool GVN::propagateEquality(Value *LHS, Value *RHS, BasicBlock *Root) { if (isa<Constant>(LHS) && isa<Constant>(RHS)) return false; - // Make sure that any constants are on the right-hand side. In general the - // best results are obtained by placing the longest lived value on the RHS. - if (isa<Constant>(LHS)) + // Prefer a constant on the right-hand side, or an Argument if no constants. + if (isa<Constant>(LHS) || (isa<Argument>(LHS) && !isa<Constant>(RHS))) std::swap(LHS, RHS); - - // If neither term is constant then bail out. This is not for correctness, - // it's just that the non-constant case is much less useful: it occurs just - // as often as the constant case but handling it hardly ever results in an - // improvement. - if (!isa<Constant>(RHS)) - return false; + assert((isa<Argument>(LHS) || isa<Instruction>(LHS)) && "Unexpected value!"); + + // If there is no obvious reason to prefer the left-hand side over the right- + // hand side, ensure the longest lived term is on the right-hand side, so the + // shortest lived term will be replaced by the longest lived. This tends to + // expose more simplifications. + uint32_t LVN = VN.lookup_or_add(LHS); + if ((isa<Argument>(LHS) && isa<Argument>(RHS)) || + (isa<Instruction>(LHS) && isa<Instruction>(RHS))) { + // Move the 'oldest' value to the right-hand side, using the value number as + // a proxy for age. + uint32_t RVN = VN.lookup_or_add(RHS); + if (LVN < RVN) { + std::swap(LHS, RHS); + LVN = RVN; + } + } // If value numbering later deduces that an instruction in the scope is equal // to 'LHS' then ensure it will be turned into 'RHS'. - addToLeaderTable(VN.lookup_or_add(LHS), RHS, Root); + addToLeaderTable(LVN, RHS, Root); // Replace all occurrences of 'LHS' with 'RHS' everywhere in the scope. As // LHS always has at least one use that is not dominated by Root, this will |