[llvm-commits] [llvm] r84158 - in /llvm/trunk: lib/CodeGen/CodePlacementOpt.cpp test/CodeGen/X86/avoid-loop-align-2.ll test/CodeGen/X86/avoid-loop-align.ll
Evan Cheng
evan.cheng at apple.com
Wed Oct 14 22:33:24 PDT 2009
On Oct 14, 2009, at 5:36 PM, Dan Gohman wrote:
> Author: djg
> Date: Wed Oct 14 19:36:22 2009
> New Revision: 84158
>
> URL: http://llvm.org/viewvc/llvm-project?rev=84158&view=rev
> Log:
> Make CodePlacementOpt align loops, rather than loop headers. The
> header is just the entry block to the loop, and it needn't be at
> the top of the loop in the code layout.
Thanks. This is aligning the destination of the back edge, right?
Have you tested the performance and code size impact of this patch?
Evan
>
> Remove the code that suppressed loop alignment for outer loops,
> so that outer loops are aligned.
>
> Modified:
> llvm/trunk/lib/CodeGen/CodePlacementOpt.cpp
> llvm/trunk/test/CodeGen/X86/avoid-loop-align-2.ll
> llvm/trunk/test/CodeGen/X86/avoid-loop-align.ll
>
> Modified: llvm/trunk/lib/CodeGen/CodePlacementOpt.cpp
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/CodeGen/CodePlacementOpt.cpp?rev=84158&r1=84157&r2=84158&view=diff
>
> ==============================================================================
> --- llvm/trunk/lib/CodeGen/CodePlacementOpt.cpp (original)
> +++ llvm/trunk/lib/CodeGen/CodePlacementOpt.cpp Wed Oct 14 19:36:22 2009
> @@ -24,7 +24,7 @@
> #include "llvm/ADT/Statistic.h"
> using namespace llvm;
>
> -STATISTIC(NumHeaderAligned, "Number of loop header aligned");
> +STATISTIC(NumLoopsAligned, "Number of loops aligned");
> STATISTIC(NumIntraElim, "Number of intra loop branches eliminated");
> STATISTIC(NumIntraMoved, "Number of intra loop branches moved");
>
> @@ -42,9 +42,6 @@
> SmallVector<std::pair<MachineBasicBlock*,MachineBasicBlock*>, 4>
> UncondJmpMBBs;
>
> - /// LoopHeaders - A list of BBs which are loop headers.
> - SmallVector<MachineBasicBlock*, 4> LoopHeaders;
> -
> public:
> static char ID;
> CodePlacementOpt() : MachineFunctionPass(&ID) {}
> @@ -62,9 +59,8 @@
>
> private:
> bool OptimizeIntraLoopEdges();
> - bool HeaderShouldBeAligned(MachineBasicBlock *MBB, MachineLoop *L,
> - SmallPtrSet<MachineBasicBlock*, 4> &DoNotAlign);
> bool AlignLoops(MachineFunction &MF);
> + bool AlignLoop(MachineFunction &MF, MachineLoop *L, unsigned Align);
> };
>
> char CodePlacementOpt::ID = 0;
> @@ -233,57 +229,12 @@
> ChangedMBBs.insert(FtMBB);
> }
> Changed = true;
> -
> - // If BB is the loop latch, we may have a new loop headr.
> - if (MBB == L->getLoopLatch()) {
> - assert(MLI->isLoopHeader(SuccMBB) &&
> - "Only succ of loop latch is not the header?");
> - if (HasOneIntraSucc && IntraSucc)
> - std::replace(LoopHeaders.begin(),LoopHeaders.end(), SuccMBB, IntraSucc);
> - }
> }
>
> ++NumIntraMoved;
> return Changed;
> }
>
> -/// HeaderShouldBeAligned - Return true if the specified loop header block
> -/// should be aligned. For now, we will not align it if all the predcessors
> -/// (i.e. loop back edges) are laid out above the header. FIXME: Do not
> -/// align small loops.
> -bool
> -CodePlacementOpt::HeaderShouldBeAligned(MachineBasicBlock *MBB, MachineLoop *L,
> - SmallPtrSet<MachineBasicBlock*, 4> &DoNotAlign) {
> - if (DoNotAlign.count(MBB))
> - return false;
> -
> - bool BackEdgeBelow = false;
> - for (MachineBasicBlock::pred_iterator PI = MBB->pred_begin(),
> - PE = MBB->pred_end(); PI != PE; ++PI) {
> - MachineBasicBlock *PredMBB = *PI;
> - if (PredMBB == MBB || PredMBB->getNumber() > MBB->getNumber()) {
> - BackEdgeBelow = true;
> - break;
> - }
> - }
> -
> - if (!BackEdgeBelow)
> - return false;
> -
> - // Ok, we are going to align this loop header. If it's an inner loop,
> - // do not align its outer loop.
> - MachineBasicBlock *PreHeader = L->getLoopPreheader();
> - if (PreHeader) {
> - MachineLoop *L = MLI->getLoopFor(PreHeader);
> - if (L) {
> - MachineBasicBlock *HeaderBlock = L->getHeader();
> - HeaderBlock->setAlignment(0);
> - DoNotAlign.insert(HeaderBlock);
> - }
> - }
> - return true;
> -}
> -
> /// AlignLoops - Align loop headers to target preferred alignments.
> ///
> bool CodePlacementOpt::AlignLoops(MachineFunction &MF) {
> @@ -295,26 +246,37 @@
> if (!Align)
> return false; // Don't care about loop alignment.
>
> - // Make sure blocks are numbered in order
> - MF.RenumberBlocks();
> + bool Changed = false;
> +
> + for (MachineLoopInfo::iterator I = MLI->begin(), E = MLI->end();
> + I != E; ++I)
> + Changed |= AlignLoop(MF, *I, Align);
> +
> + return Changed;
> +}
>
> +bool CodePlacementOpt::AlignLoop(MachineFunction &MF, MachineLoop *L,
> + unsigned Align) {
> bool Changed = false;
> - SmallPtrSet<MachineBasicBlock*, 4> DoNotAlign;
> - for (unsigned i = 0, e = LoopHeaders.size(); i != e; ++i) {
> - MachineBasicBlock *HeaderMBB = LoopHeaders[i];
> - MachineBasicBlock *PredMBB = prior(MachineFunction::iterator(HeaderMBB));
> - MachineLoop *L = MLI->getLoopFor(HeaderMBB);
> - if (L == MLI->getLoopFor(PredMBB))
> - // If previously BB is in the same loop, don't align this BB. We want
> - // to prevent adding noop's inside a loop.
> - continue;
> - if (HeaderShouldBeAligned(HeaderMBB, L, DoNotAlign)) {
> - HeaderMBB->setAlignment(Align);
> - Changed = true;
> - ++NumHeaderAligned;
> - }
> +
> + // Do alignment for nested loops.
> + for (MachineLoop::iterator I = L->begin(), E = L->end(); I != E; ++I)
> + Changed |= AlignLoop(MF, *I, Align);
> +
> + MachineBasicBlock *TopMBB = L->getHeader();
> + if (TopMBB == MF.begin()) return Changed;
> +
> + MachineBasicBlock *PredMBB = prior(MachineFunction::iterator(TopMBB));
> + while (MLI->getLoopFor(PredMBB) == L) {
> + TopMBB = PredMBB;
> + if (TopMBB == MF.begin()) return Changed;
> + PredMBB = prior(MachineFunction::iterator(TopMBB));
> }
>
> + TopMBB->setAlignment(Align);
> + Changed = true;
> + ++NumLoopsAligned;
> +
> return Changed;
> }
>
> @@ -326,7 +288,7 @@
> TLI = MF.getTarget().getTargetLowering();
> TII = MF.getTarget().getInstrInfo();
>
> - // Analyze the BBs first and keep track of loop headers and BBs that
> + // Analyze the BBs first and keep track of BBs that
> // end with an unconditional jmp to another block in the same loop.
> for (MachineFunction::iterator I = MF.begin(), E = MF.end(); I != E; ++I) {
> MachineBasicBlock *MBB = I;
> @@ -335,8 +297,6 @@
> MachineLoop *L = MLI->getLoopFor(MBB);
> if (!L)
> continue;
> - if (MLI->isLoopHeader(MBB))
> - LoopHeaders.push_back(MBB);
>
> MachineBasicBlock *TBB = 0, *FBB = 0;
> SmallVector<MachineOperand, 4> Cond;
> @@ -352,7 +312,6 @@
>
> ChangedMBBs.clear();
> UncondJmpMBBs.clear();
> - LoopHeaders.clear();
>
> return Changed;
> }
>
> Modified: llvm/trunk/test/CodeGen/X86/avoid-loop-align-2.ll
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/CodeGen/X86/avoid-loop-align-2.ll?rev=84158&r1=84157&r2=84158&view=diff
>
> ==============================================================================
> --- llvm/trunk/test/CodeGen/X86/avoid-loop-align-2.ll (original)
> +++ llvm/trunk/test/CodeGen/X86/avoid-loop-align-2.ll Wed Oct 14 19:36:22 2009
> @@ -1,4 +1,8 @@
> -; RUN: llc < %s -march=x86 | grep align | count 3
> +; RUN: llc < %s -march=x86 | grep align | count 4
> +
> +; TODO: Is it a good idea to align inner loops? It's hard to know without
> +; knowing what their trip counts are, or other dynamic information. For
> +; now, CodeGen aligns all loops.
>
> @x = external global i32* ; <i32**> [#uses=1]
>
>
> Modified: llvm/trunk/test/CodeGen/X86/avoid-loop-align.ll
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/CodeGen/X86/avoid-loop-align.ll?rev=84158&r1=84157&r2=84158&view=diff
>
> ==============================================================================
> --- llvm/trunk/test/CodeGen/X86/avoid-loop-align.ll (original)
> +++ llvm/trunk/test/CodeGen/X86/avoid-loop-align.ll Wed Oct 14 19:36:22 2009
> @@ -1,4 +1,11 @@
> -; RUN: llc < %s -mtriple=i386-apple-darwin | grep align | count 1
> +; RUN: llc < %s -mtriple=i386-apple-darwin | FileCheck %s
> +
> +; CodeGen should align the top of the loop, which differs from the loop
> +; header in this case.
> +
> +; CHECK: jmp LBB1_2
> +; CHECK: .align
> +; CHECK: LBB1_1:
>
> @A = common global [100 x i32] zeroinitializer, align 32 ; <[100 x i32]*> [#uses=1]
>
>
>
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