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Add dominance check for the instruction being hoisted. 

For example, MachineLICM should not hoist a load that is not guaranteed to be executed.
Radar 10254254.

llvm-svn: 141689
This commit is contained in:
Devang Patel 2011-10-11 18:09:58 +00:00
parent ff2c52ce63
commit 453d401a51
5 changed files with 89 additions and 9 deletions
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47
llvm/lib/CodeGen/MachineLICM.cpp
View File

@ -91,6 +91,11 @@ namespace {
// For each opcode, keep a list of potential CSE instructions.
DenseMap<unsigned, std::vector<const MachineInstr*> > CSEMap;
// If a MBB does not dominate loop exiting blocks then it may not safe
// to hoist loads from this block.
bool CurrentMBBDominatesLoopExitingBlocks;
bool NeedToCheckMBBDominance;
public:
static char ID; // Pass identification, replacement for typeid
MachineLICM() :
@ -194,6 +199,10 @@ namespace {
/// hoist the given loop invariant.
bool IsProfitableToHoist(MachineInstr &MI);
/// IsGuaranteedToExecute - Check if this mbb is guaranteed to execute.
/// If not then a load from this mbb may not be safe to hoist.
bool IsGuaranteedToExecute(MachineBasicBlock *BB);
/// HoistRegion - Walk the specified region of the CFG (defined by all
/// blocks dominated by the specified block, and that are in the current
/// loop) in depth first order w.r.t the DominatorTree. This allows us to
@ -295,6 +304,9 @@ bool MachineLICM::runOnMachineFunction(MachineFunction &MF) {
MRI = &MF.getRegInfo();
InstrItins = TM->getInstrItineraryData();
AllocatableSet = TRI->getAllocatableSet(MF);
// Stay conservative.
CurrentMBBDominatesLoopExitingBlocks = false;
NeedToCheckMBBDominance = true;
if (PreRegAlloc) {
// Estimate register pressure during pre-regalloc pass.
@ -459,6 +471,7 @@ void MachineLICM::HoistRegionPostRA() {
++PhysRegDefs[*AS];
}
NeedToCheckMBBDominance = true;
for (MachineBasicBlock::iterator
MII = BB->begin(), E = BB->end(); MII != E; ++MII) {
MachineInstr *MI = &*MII;
@ -552,6 +565,30 @@ void MachineLICM::HoistPostRA(MachineInstr *MI, unsigned Def) {
Changed = true;
}
// IsGuaranteedToExecute - Check if this mbb is guaranteed to execute.
// If not then a load from this mbb may not be safe to hoist.
bool MachineLICM::IsGuaranteedToExecute(MachineBasicBlock *BB) {
// Do not check if we already have checked it once.
if (NeedToCheckMBBDominance == false)
return CurrentMBBDominatesLoopExitingBlocks;
NeedToCheckMBBDominance = false;
if (BB != CurLoop->getHeader()) {
// Check loop exiting blocks.
SmallVector<MachineBasicBlock*, 8> CurrentLoopExitingBlocks;
CurLoop->getExitingBlocks(CurrentLoopExitingBlocks);
for (unsigned i = 0, e = CurrentLoopExitingBlocks.size(); i != e; ++i)
if (!DT->dominates(BB, CurrentLoopExitingBlocks[i])) {
CurrentMBBDominatesLoopExitingBlocks = false;
return CurrentMBBDominatesLoopExitingBlocks;
}
}
CurrentMBBDominatesLoopExitingBlocks = true;
return CurrentMBBDominatesLoopExitingBlocks;
}
/// HoistRegion - Walk the specified region of the CFG (defined by all blocks
/// dominated by the specified block, and that are in the current loop) in depth
/// first order w.r.t the DominatorTree. This allows us to visit definitions
@ -578,6 +615,7 @@ void MachineLICM::HoistRegion(MachineDomTreeNode *N, bool IsHeader) {
// Remember livein register pressure.
BackTrace.push_back(RegPressure);
NeedToCheckMBBDominance = true;
for (MachineBasicBlock::iterator
MII = BB->begin(), E = BB->end(); MII != E; ) {
MachineBasicBlock::iterator NextMII = MII; ++NextMII;
@ -711,7 +749,14 @@ bool MachineLICM::IsLICMCandidate(MachineInstr &I) {
bool DontMoveAcrossStore = true;
if (!I.isSafeToMove(TII, AA, DontMoveAcrossStore))
return false;
// If it is load then check if it is guaranteed to execute by making sure that
// it dominates all exiting blocks. If it doesn't, then there is a path out of
// the loop which does not execute this load, so we can't hoist it.
// Stores and side effects are already checked by isSafeToMove.
if (I.getDesc().mayLoad() && !IsGuaranteedToExecute(I.getParent()))
return false;
return true;
}

3
llvm/test/CodeGen/ARM/lsr-unfolded-offset.ll
View File

@ -4,12 +4,11 @@
; register pressure and therefore spilling. There is more room for improvement
; here.
; CHECK: sub sp, #{{32|28|24}}
; CHECK: sub sp, #{{40|32|28|24}}
; CHECK: %for.inc
; CHECK: ldr{{(.w)?}} r{{.*}}, [sp, #
; CHECK: ldr{{(.w)?}} r{{.*}}, [sp, #
; CHECK: ldr{{(.w)?}} r{{.*}}, [sp, #
; CHECK: add
target datalayout = "e-p:32:32:32-i1:8:32-i8:8:32-i16:16:32-i32:32:32-i64:32:32-f32:32:32-f64:32:32-v64:32:64-v128:32:128-a0:0:32-n32"

36
llvm/test/CodeGen/X86/licm-dominance.ll Normal file
View File

@ -0,0 +1,36 @@
; RUN: llc -asm-verbose=false < %s | FileCheck %s
; MachineLICM should check dominance before hoisting instructions.
; CHECK: jne LBB0_3
; CHECK-NEXT: xorb %al, %al
; CHECK-NEXT: testb %al, %al
target datalayout = "e-p:64:64:64-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:64:64-f32:32:32-f64:64:64-v64:64:64-v128:128:128-a0:0:64-s0:64:64-f80:128:128-n8:16:32:64"
target triple = "x86_64-apple-macosx10.7.2"
define void @CMSColorWorldCreateParametricData() nounwind uwtable optsize ssp {
entry:
br label %for.body.i
for.body.i:
br i1 undef, label %for.inc.i, label %if.then26.i
if.then26.i:
br i1 undef, label %if.else.i.i, label %lor.lhs.false.i.i
if.else.i.i:
br i1 undef, label %lor.lhs.false.i.i, label %if.then116.i.i
lor.lhs.false.i.i:
br i1 undef, label %for.inc.i, label %if.then116.i.i
if.then116.i.i:
unreachable
for.inc.i:
%cmp17.i = icmp ult i64 undef, undef
br i1 %cmp17.i, label %for.body.i, label %if.end28.i
if.end28.i:
ret void
}

2
llvm/test/CodeGen/X86/licm-nested.ll
View File

@ -1,4 +1,4 @@
; RUN: llc -mtriple=x86_64-apple-darwin -march=x86-64 < %s -o /dev/null -stats -info-output-file - | grep machine-licm | grep 3
; RUN: llc -mtriple=x86_64-apple-darwin -march=x86-64 < %s -o /dev/null -stats -info-output-file - | grep machine-licm | grep 2
; MachineLICM should be able to hoist the symbolic addresses out of
; the inner loops.

10
llvm/test/CodeGen/X86/sink-hoist.ll
View File

@ -102,6 +102,7 @@ entry:
br label %bb60
bb: ; preds = %bb60
%i.0 = phi i32 [ 0, %bb60 ] ; <i32> [#uses=2]
%0 = bitcast float* %x_addr.0 to <4 x float>* ; <<4 x float>*> [#uses=1]
%1 = load <4 x float>* %0, align 16 ; <<4 x float>> [#uses=4]
%tmp20 = bitcast <4 x float> %1 to <4 x i32> ; <<4 x i32>> [#uses=1]
@ -129,15 +130,14 @@ bb: ; preds = %bb60
%5 = getelementptr float* %x_addr.0, i64 4 ; <float*> [#uses=1]
%6 = getelementptr float* %y_addr.0, i64 4 ; <float*> [#uses=1]
%7 = add i32 %i.0, 4 ; <i32> [#uses=1]
br label %bb60
%8 = load i32* %n, align 4 ; <i32> [#uses=1]
%9 = icmp sgt i32 %8, %7 ; <i1> [#uses=1]
br i1 %9, label %bb60, label %return
bb60: ; preds = %bb, %entry
%i.0 = phi i32 [ 0, %entry ], [ %7, %bb ] ; <i32> [#uses=2]
%x_addr.0 = phi float* [ %x, %entry ], [ %5, %bb ] ; <float*> [#uses=2]
%y_addr.0 = phi float* [ %y, %entry ], [ %6, %bb ] ; <float*> [#uses=2]
%8 = load i32* %n, align 4 ; <i32> [#uses=1]
%9 = icmp sgt i32 %8, %i.0 ; <i1> [#uses=1]
br i1 %9, label %bb, label %return
br label %bb
return: ; preds = %bb60
ret void