From: Evan Cheng Date: Tue, 17 Aug 2010 01:20:36 +0000 (+0000) Subject: PHI elimination should not break back edge. It can cause some significant code placem... X-Git-Url: http://plrg.eecs.uci.edu/git/?a=commitdiff_plain;h=97b9b97853d7e4fbb5c8460ef28126013c76e9a9;p=oota-llvm.git PHI elimination should not break back edge. It can cause some significant code placement issues. rdar://8263994 good: LBB0_2: mov r2, r0 . . . mov r1, r2 bne LBB0_2 bad: LBB0_2: mov r2, r0 . . . @ BB#3: mov r1, r2 b LBB0_2 git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@111221 91177308-0d34-0410-b5e6-96231b3b80d8 --- diff --git a/lib/CodeGen/MachineBasicBlock.cpp b/lib/CodeGen/MachineBasicBlock.cpp index a27ee479433..895653d18de 100644 --- a/lib/CodeGen/MachineBasicBlock.cpp +++ b/lib/CodeGen/MachineBasicBlock.cpp @@ -439,6 +439,14 @@ MachineBasicBlock::SplitCriticalEdge(MachineBasicBlock *Succ, Pass *P) { if (TII->AnalyzeBranch(*this, TBB, FBB, Cond)) return NULL; + // Avoid splitting backedges of loops. It would introduce small out-of-line + // blocks into the loop which is very bad for code placement. + if (this == Succ) + return NULL; + MachineLoopInfo *MLI = P->getAnalysisIfAvailable(); + if (MLI->isLoopHeader(Succ)) + return NULL; + MachineBasicBlock *NMBB = MF->CreateMachineBasicBlock(); MF->insert(llvm::next(MachineFunction::iterator(this)), NMBB); DEBUG(dbgs() << "PHIElimination splitting critical edge:" @@ -471,8 +479,7 @@ MachineBasicBlock::SplitCriticalEdge(MachineBasicBlock *Succ, Pass *P) { P->getAnalysisIfAvailable()) MDT->addNewBlock(NMBB, this); - if (MachineLoopInfo *MLI = - P->getAnalysisIfAvailable()) + if (MLI) if (MachineLoop *TIL = MLI->getLoopFor(this)) { // If one or the other blocks were not in a loop, the new block is not // either, and thus LI doesn't need to be updated. diff --git a/lib/CodeGen/PHIElimination.cpp b/lib/CodeGen/PHIElimination.cpp index 7bf0aa23af3..105f20b4489 100644 --- a/lib/CodeGen/PHIElimination.cpp +++ b/lib/CodeGen/PHIElimination.cpp @@ -20,6 +20,7 @@ #include "llvm/CodeGen/MachineDominators.h" #include "llvm/CodeGen/MachineInstr.h" #include "llvm/CodeGen/MachineInstrBuilder.h" +#include "llvm/CodeGen/MachineLoopInfo.h" #include "llvm/CodeGen/MachineRegisterInfo.h" #include "llvm/Target/TargetInstrInfo.h" #include "llvm/Function.h" @@ -44,9 +45,9 @@ char &llvm::PHIEliminationID = PHIElimination::ID; void llvm::PHIElimination::getAnalysisUsage(AnalysisUsage &AU) const { AU.addPreserved(); + AU.addRequired(); AU.addPreserved(); - // rdar://7401784 This would be nice: - // AU.addPreservedID(MachineLoopInfoID); + AU.addPreservedID(MachineLoopInfoID); MachineFunctionPass::getAnalysisUsage(AU); } @@ -382,6 +383,7 @@ bool llvm::PHIElimination::SplitPHIEdges(MachineFunction &MF, if (MBB.empty() || !MBB.front().isPHI() || MBB.isLandingPad()) return false; // Quick exit for basic blocks without PHIs. + bool Changed = false; for (MachineBasicBlock::const_iterator BBI = MBB.begin(), BBE = MBB.end(); BBI != BBE && BBI->isPHI(); ++BBI) { for (unsigned i = 1, e = BBI->getNumOperands(); i != e; i += 2) { @@ -391,7 +393,7 @@ bool llvm::PHIElimination::SplitPHIEdges(MachineFunction &MF, // (not considering PHI nodes). If the register is live in to this block // anyway, we would gain nothing from splitting. if (!LV.isLiveIn(Reg, MBB) && LV.isLiveOut(Reg, *PreMBB)) - PreMBB->SplitCriticalEdge(&MBB, this); + Changed |= PreMBB->SplitCriticalEdge(&MBB, this) != 0; } } return true; diff --git a/test/CodeGen/ARM/code-placement.ll b/test/CodeGen/ARM/code-placement.ll new file mode 100644 index 00000000000..25c556889fc --- /dev/null +++ b/test/CodeGen/ARM/code-placement.ll @@ -0,0 +1,29 @@ +; RUN: llc < %s -mtriple=armv7-apple-darwin | FileCheck %s +; PHI elimination shouldn't break backedge. +; rdar://8263994 + +%struct.list_data_s = type { i16, i16 } +%struct.list_head = type { %struct.list_head*, %struct.list_data_s* } + +define arm_apcscc %struct.list_head* @t(%struct.list_head* %list) nounwind { +entry: + %0 = icmp eq %struct.list_head* %list, null + br i1 %0, label %bb2, label %bb + +bb: +; CHECK: LBB0_2: +; CHECK: bne LBB0_2 +; CHECK-NOT: b LBB0_2 +; CHECK: bx lr + %list_addr.05 = phi %struct.list_head* [ %2, %bb ], [ %list, %entry ] + %next.04 = phi %struct.list_head* [ %list_addr.05, %bb ], [ null, %entry ] + %1 = getelementptr inbounds %struct.list_head* %list_addr.05, i32 0, i32 0 + %2 = load %struct.list_head** %1, align 4 + store %struct.list_head* %next.04, %struct.list_head** %1, align 4 + %3 = icmp eq %struct.list_head* %2, null + br i1 %3, label %bb2, label %bb + +bb2: + %next.0.lcssa = phi %struct.list_head* [ null, %entry ], [ %list_addr.05, %bb ] + ret %struct.list_head* %next.0.lcssa +} diff --git a/test/CodeGen/X86/lsr-reuse.ll b/test/CodeGen/X86/lsr-reuse.ll index b7e69b84bf8..d2ff58be105 100644 --- a/test/CodeGen/X86/lsr-reuse.ll +++ b/test/CodeGen/X86/lsr-reuse.ll @@ -464,7 +464,7 @@ bb5: ; preds = %bb3, %entry ; And the one at %bb68, where we want to be sure to use superhero mode: -; CHECK: BB10_10: +; CHECK: BB10_9: ; CHECK-NEXT: movaps 48(%r{{[^,]*}}), %xmm{{.*}} ; CHECK-NEXT: mulps %xmm{{.*}}, %xmm{{.*}} ; CHECK-NEXT: movaps 32(%r{{[^,]*}}), %xmm{{.*}} @@ -484,7 +484,7 @@ bb5: ; preds = %bb3, %entry ; CHECK-NEXT: addq $64, %r{{.*}} ; CHECK-NEXT: addq $64, %r{{.*}} ; CHECK-NEXT: addq $-16, %r{{.*}} -; CHECK-NEXT: BB10_11: +; CHECK-NEXT: BB10_10: ; CHECK-NEXT: cmpq $15, %r{{.*}} ; CHECK-NEXT: jg