diff options
| -rw-r--r-- | lib/CodeGen/MachineBlockPlacement.cpp | 58 | ||||
| -rw-r--r-- | test/CodeGen/X86/block-placement.ll | 25 |
2 files changed, 58 insertions, 25 deletions
diff --git a/lib/CodeGen/MachineBlockPlacement.cpp b/lib/CodeGen/MachineBlockPlacement.cpp index 2fef9c4..e83ae93 100644 --- a/lib/CodeGen/MachineBlockPlacement.cpp +++ b/lib/CodeGen/MachineBlockPlacement.cpp @@ -355,6 +355,10 @@ MachineBasicBlock *MachineBlockPlacement::selectBestSuccessor( DEBUG(dbgs() << " " << getBlockName(*SI) << " -> Already merged!\n"); continue; } + if (*SI != *SuccChain.begin()) { + DEBUG(dbgs() << " " << getBlockName(*SI) << " -> Mid chain!\n"); + continue; + } uint32_t SuccWeight = MBPI->getEdgeWeight(BB, *SI); BranchProbability SuccProb(SuccWeight / WeightScale, SumWeight); @@ -472,7 +476,6 @@ void MachineBlockPlacement::buildChain( assert(BB); assert(BlockToChain[BB] == &Chain); assert(*Chain.begin() == BB); - SmallVector<MachineOperand, 4> Cond; // For AnalyzeBranch. MachineFunction &F = *BB->getParent(); MachineFunction::iterator PrevUnplacedBlockIt = F.begin(); @@ -485,26 +488,9 @@ void MachineBlockPlacement::buildChain( assert(*llvm::prior(Chain.end()) == BB); MachineBasicBlock *BestSucc = 0; - // Check for unreasonable branches, and forcibly merge the existing layout - // successor for them. We can handle cases that AnalyzeBranch can't: jump - // tables etc are fine. The case we want to handle specially is when there - // is potential fallthrough, but the branch cannot be analyzed. This - // includes blocks without terminators as well as other cases. - Cond.clear(); - MachineBasicBlock *TBB = 0, *FBB = 0; // For AnalyzeBranch. - if (TII->AnalyzeBranch(*BB, TBB, FBB, Cond) && BB->canFallThrough()) { - MachineFunction::iterator I(BB), NextI(llvm::next(I)); - // Ensure that the layout successor is a viable block, as we know that - // fallthrough is a possibility. Note that this may not be a valid block - // in the loop, but we allow that to cope with degenerate situations. - assert(NextI != BB->getParent()->end()); - BestSucc = NextI; - } - - // Otherwise, look for the best viable successor if there is one to place - // immediately after this block. - if (!BestSucc) - BestSucc = selectBestSuccessor(BB, Chain, BlockFilter); + // Look for the best viable successor if there is one to place immediately + // after this block. + BestSucc = selectBestSuccessor(BB, Chain, BlockFilter); // If an immediate successor isn't available, look for the best viable // block among those we've identified as not violating the loop's CFG at @@ -624,9 +610,32 @@ void MachineBlockPlacement::buildLoopChains(MachineFunction &F, void MachineBlockPlacement::buildCFGChains(MachineFunction &F) { // Ensure that every BB in the function has an associated chain to simplify // the assumptions of the remaining algorithm. - for (MachineFunction::iterator FI = F.begin(), FE = F.end(); FI != FE; ++FI) - BlockToChain[&*FI] = - new (ChainAllocator.Allocate()) BlockChain(BlockToChain, &*FI); + SmallVector<MachineOperand, 4> Cond; // For AnalyzeBranch. + for (MachineFunction::iterator FI = F.begin(), FE = F.end(); FI != FE; ++FI) { + MachineBasicBlock *BB = FI; + BlockChain *&Chain = BlockToChain[BB]; + Chain = new (ChainAllocator.Allocate()) BlockChain(BlockToChain, BB); + // Also, merge any blocks which we cannot reason about and must preserve + // the exact fallthrough behavior for. + for (;;) { + Cond.clear(); + MachineBasicBlock *TBB = 0, *FBB = 0; // For AnalyzeBranch. + if (!TII->AnalyzeBranch(*BB, TBB, FBB, Cond) || !FI->canFallThrough()) + break; + + MachineFunction::iterator NextFI(llvm::next(FI)); + MachineBasicBlock *NextBB = NextFI; + // Ensure that the layout successor is a viable block, as we know that + // fallthrough is a possibility. + assert(NextFI != FE && "Can't fallthrough past the last block."); + DEBUG(dbgs() << "Pre-merging due to unanalyzable fallthrough: " + << getBlockName(BB) << " -> " << getBlockName(NextBB) + << "\n"); + Chain->merge(NextBB, 0); + FI = NextFI; + BB = NextBB; + } + } // Build any loop-based chains. for (MachineLoopInfo::iterator LI = MLI->begin(), LE = MLI->end(); LI != LE; @@ -692,7 +701,6 @@ void MachineBlockPlacement::buildCFGChains(MachineFunction &F) { // Splice the blocks into place. MachineFunction::iterator InsertPos = F.begin(); - SmallVector<MachineOperand, 4> Cond; // For AnalyzeBranch. for (BlockChain::iterator BI = FunctionChain.begin(), BE = FunctionChain.end(); BI != BE; ++BI) { diff --git a/test/CodeGen/X86/block-placement.ll b/test/CodeGen/X86/block-placement.ll index 6220ae3..859a702 100644 --- a/test/CodeGen/X86/block-placement.ll +++ b/test/CodeGen/X86/block-placement.ll @@ -393,3 +393,28 @@ exit: %merge = phi i32 [ 3, %step ], [ 6, %entry ] ret i32 %merge } + +define void @fpcmp_unanalyzable_branch(i1 %cond) { +entry: + br i1 %cond, label %entry.if.then_crit_edge, label %lor.lhs.false + +entry.if.then_crit_edge: + %.pre14 = load i8* undef, align 1, !tbaa !0 + br label %if.then + +lor.lhs.false: + br i1 undef, label %if.end, label %exit + +exit: + %cmp.i = fcmp une double 0.000000e+00, undef + br i1 %cmp.i, label %if.then, label %if.end + +if.then: + %0 = phi i8 [ %.pre14, %entry.if.then_crit_edge ], [ undef, %exit ] + %1 = and i8 %0, 1 + store i8 %1, i8* undef, align 4, !tbaa !0 + br label %if.end + +if.end: + ret void +} |