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[IROutliner] Accomodate blocks containing PHINodes with one entry outside the region and others inside the region. 

When a PHINode has an incoming block from outside the region, it must be handled specially when assigning a global value number to each incoming value. A PHINode has multiple predecessors, and we must handle this case rather than only the single predecessor case.

Reviewer: paquette

Differential Revision: https://reviews.llvm.org/D124777
This commit is contained in:
Andrew Litteken 2022-05-01 18:14:18 -05:00
parent a385645b47
commit e38f014c40
3 changed files with 187 additions and 2 deletions
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41
llvm/lib/Transforms/IPO/IROutliner.cpp
View File

@ -283,11 +283,13 @@ void OutlinableRegion::splitCandidate() {
BasicBlock::iterator It = StartInst->getIterator();
EndBB = BackInst->getParent();
BasicBlock *IBlock;
BasicBlock *PHIPredBlock = nullptr;
bool EndBBTermAndBackInstDifferent = EndBB->getTerminator() != BackInst;
while (PHINode *PN = dyn_cast<PHINode>(&*It)) {
unsigned NumPredsOutsideRegion = 0;
for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
if (!BBSet.contains(PN->getIncomingBlock(i))) {
PHIPredBlock = PN->getIncomingBlock(i);
++NumPredsOutsideRegion;
continue;
}
@ -296,8 +298,10 @@ void OutlinableRegion::splitCandidate() {
// the same as the final block of the OutlinableRegion. If this is the
// case, the branch from this block must also be outlined to be valid.
IBlock = PN->getIncomingBlock(i);
if (IBlock == EndBB && EndBBTermAndBackInstDifferent)
if (IBlock == EndBB && EndBBTermAndBackInstDifferent) {
PHIPredBlock = PN->getIncomingBlock(i);
++NumPredsOutsideRegion;
}
}
if (NumPredsOutsideRegion > 1)
@ -336,6 +340,10 @@ void OutlinableRegion::splitCandidate() {
StartBB = PrevBB->splitBasicBlock(StartInst, OriginalName + "_to_outline");
PrevBB->replaceSuccessorsPhiUsesWith(PrevBB, StartBB);
// If there was a PHINode with an incoming block outside the region,
// make sure is correctly updated in the newly split block.
if (PHIPredBlock)
PrevBB->replaceSuccessorsPhiUsesWith(PHIPredBlock, PrevBB);
CandidateSplit = true;
if (!BackInst->isTerminator()) {
@ -379,6 +387,25 @@ void OutlinableRegion::reattachCandidate() {
assert(StartBB != nullptr && "StartBB for Candidate is not defined!");
assert(PrevBB->getTerminator() && "Terminator removed from PrevBB!");
// Make sure PHINode references to the block we are merging into are
// updated to be incoming blocks from the predecessor to the current block.
// NOTE: If this is updated such that the outlined block can have more than
// one incoming block to a PHINode, this logic will have to updated
// to handle multiple precessors instead.
// We only need to update this if the outlined section contains a PHINode, if
// it does not, then the incoming block was never changed in the first place.
// On the other hand, if PrevBB has no predecessors, it means that all
// incoming blocks to the first block are contained in the region, and there
// will be nothing to update.
Instruction *StartInst = (*Candidate->begin()).Inst;
if (isa<PHINode>(StartInst) && !PrevBB->hasNPredecessors(0)) {
assert(!PrevBB->hasNPredecessorsOrMore(2) &&
"PrevBB has more than one predecessor. Should be 0 or 1.");
BasicBlock *BeforePrevBB = PrevBB->getSinglePredecessor();
PrevBB->replaceSuccessorsPhiUsesWith(PrevBB, BeforePrevBB);
}
PrevBB->getTerminator()->eraseFromParent();
// If we reattaching after outlining, we iterate over the phi nodes to
@ -1183,7 +1210,17 @@ static Optional<unsigned> getGVNForPHINode(OutlinableRegion &Region,
assert(Cand.getStartBB() == IncomingBlock &&
"Unknown basic block used in exit path PHINode.");
BasicBlock *PrevBlock = IncomingBlock->getSinglePredecessor();
BasicBlock *PrevBlock = nullptr;
// Iterate over the predecessors to the incoming block of the
// PHINode, when we find a block that is not contained in the region
// we know that this is the first block that we split from, and should
// have a valid global value numbering.
for (BasicBlock *Pred : predecessors(IncomingBlock))
if (!Blocks.contains(Pred)) {
PrevBlock = Pred;
break;
}
assert(PrevBlock && "Expected a predecessor not in the reigon!");
OGVN = Cand.getGVN(PrevBlock);
}
GVN = OGVN.getValue();

76
llvm/test/Transforms/IROutliner/no-external-block-entries.ll Normal file
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@ -0,0 +1,76 @@
; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --include-generated-funcs
; RUN: opt -S -verify -iroutliner -ir-outlining-no-cost < %s | FileCheck %s
; When the an outlined section contains a PHINode no incoming blocks outside
; the region, we need to make sure that we do not try to reassign
; the incoming blocks when splitting and reattaching the region.
define void @fn1() local_unnamed_addr #0 {
entry:
br label %block_2
block_1:
%a = phi i32 [ 0, %block_2], [ 1, %intermediate_block_1 ]
br i1 0, label %block_3, label %block_2
intermediate_block_1:
br label %block_1
block_2:
br i1 0, label %block_3, label %block_1
block_3:
%b = phi i32 [ 0, %block_2 ], [ 1, %block_1 ]
br label %block_5
block_4:
%c = phi i32 [ 0, %block_5 ], [ 1, %intermediate_block_2 ]
br i1 0, label %block_6, label %block_5
intermediate_block_2:
br label %block_4
block_5:
br i1 0, label %block_6, label %block_4
block_6:
unreachable
}
; CHECK-LABEL: @fn1(
; CHECK-NEXT: entry:
; CHECK-NEXT: [[B_CE_LOC:%.*]] = alloca i32, align 4
; CHECK-NEXT: [[LT_CAST:%.*]] = bitcast i32* [[B_CE_LOC]] to i8*
; CHECK-NEXT: call void @llvm.lifetime.start.p0i8(i64 -1, i8* [[LT_CAST]])
; CHECK-NEXT: call void @outlined_ir_func_0(i32* [[B_CE_LOC]], i32 0)
; CHECK-NEXT: [[B_CE_RELOAD:%.*]] = load i32, i32* [[B_CE_LOC]], align 4
; CHECK-NEXT: call void @llvm.lifetime.end.p0i8(i64 -1, i8* [[LT_CAST]])
; CHECK-NEXT: br label [[BLOCK_3:%.*]]
; CHECK: block_3:
; CHECK-NEXT: [[B:%.*]] = phi i32 [ [[B_CE_RELOAD]], [[ENTRY:%.*]] ]
; CHECK-NEXT: call void @outlined_ir_func_0(i32* null, i32 -1)
; CHECK-NEXT: br label [[BLOCK_6:%.*]]
; CHECK: block_6:
; CHECK-NEXT: unreachable
;
;
; CHECK-LABEL: define internal void @outlined_ir_func_0(
; CHECK-NEXT: newFuncRoot:
; CHECK-NEXT: br label [[ENTRY_TO_OUTLINE:%.*]]
; CHECK: entry_to_outline:
; CHECK-NEXT: br label [[BLOCK_2:%.*]]
; CHECK: block_1:
; CHECK-NEXT: [[A:%.*]] = phi i32 [ 0, [[BLOCK_2]] ], [ 1, [[INTERMEDIATE_BLOCK_1:%.*]] ]
; CHECK-NEXT: br i1 false, label [[BLOCK_3_SPLIT:%.*]], label [[BLOCK_2]]
; CHECK: intermediate_block_1:
; CHECK-NEXT: br label [[BLOCK_1:%.*]]
; CHECK: block_2:
; CHECK-NEXT: br i1 false, label [[BLOCK_3_SPLIT]], label [[BLOCK_1]]
; CHECK: block_3.split:
; CHECK-NEXT: [[B_CE:%.*]] = phi i32 [ 0, [[BLOCK_2]] ], [ 1, [[BLOCK_1]] ]
; CHECK-NEXT: br label [[BLOCK_3_EXITSTUB:%.*]]
; CHECK: block_3.exitStub:
; CHECK-NEXT: switch i32 [[TMP1:%.*]], label [[FINAL_BLOCK_0:%.*]] [
; CHECK-NEXT: i32 0, label [[OUTPUT_BLOCK_0_0:%.*]]
; CHECK-NEXT: ]
; CHECK: output_block_0_0:
; CHECK-NEXT: store i32 [[B_CE]], i32* [[TMP0:%.*]], align 4
; CHECK-NEXT: br label [[FINAL_BLOCK_0]]
; CHECK: final_block_0:
; CHECK-NEXT: ret void
;

72
llvm/test/Transforms/IROutliner/one-external-incoming-block-phi-node.ll Normal file
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@ -0,0 +1,72 @@
; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --include-generated-funcs
; RUN: opt -S -verify -iroutliner -ir-outlining-no-cost < %s | FileCheck %s
; When the an outlined section contains a PHINode with an incoming block
; outside of the region, the predecessors to be handled specially to ensure that
; a global value is properly assigned. This ensures that there is no crash
; in that situation.
define void @fn1() local_unnamed_addr #0 {
entry:
br label %block_1
block_1:
%a = phi i32 [ 0, %block_2], [ 1, %entry ]
br i1 0, label %block_3, label %block_2
block_2:
br i1 0, label %block_3, label %block_1
block_3:
%b = phi i32 [ 0, %block_2 ], [ 1, %block_1 ]
br label %block_4
block_4:
%c = phi i32 [ 0, %block_5 ], [ 1, %block_3 ]
br i1 0, label %block_6, label %block_5
block_5:
br i1 0, label %block_6, label %block_4
block_6:
unreachable
}
; CHECK-LABEL: @fn1(
; CHECK-NEXT: entry:
; CHECK-NEXT: [[B_CE_LOC:%.*]] = alloca i32, align 4
; CHECK-NEXT: [[LT_CAST:%.*]] = bitcast i32* [[B_CE_LOC]] to i8*
; CHECK-NEXT: call void @llvm.lifetime.start.p0i8(i64 -1, i8* [[LT_CAST]])
; CHECK-NEXT: call void @outlined_ir_func_0(i32* [[B_CE_LOC]], i32 0)
; CHECK-NEXT: [[B_CE_RELOAD:%.*]] = load i32, i32* [[B_CE_LOC]], align 4
; CHECK-NEXT: call void @llvm.lifetime.end.p0i8(i64 -1, i8* [[LT_CAST]])
; CHECK-NEXT: br label [[BLOCK_3:%.*]]
; CHECK: block_3:
; CHECK-NEXT: [[B:%.*]] = phi i32 [ [[B_CE_RELOAD]], [[ENTRY:%.*]] ]
; CHECK-NEXT: call void @outlined_ir_func_0(i32* null, i32 -1)
; CHECK-NEXT: br label [[BLOCK_6:%.*]]
; CHECK: block_6:
; CHECK-NEXT: unreachable
;
;
; CHECK-LABEL: define internal void @outlined_ir_func_0(
; CHECK-NEXT: newFuncRoot:
; CHECK-NEXT: br label [[ENTRY_TO_OUTLINE:%.*]]
; CHECK: entry_to_outline:
; CHECK-NEXT: br label [[BLOCK_1:%.*]]
; CHECK: block_1:
; CHECK-NEXT: [[A:%.*]] = phi i32 [ 0, [[BLOCK_2:%.*]] ], [ 1, [[ENTRY_TO_OUTLINE]] ]
; CHECK-NEXT: br i1 false, label [[BLOCK_3_SPLIT:%.*]], label [[BLOCK_2]]
; CHECK: block_2:
; CHECK-NEXT: br i1 false, label [[BLOCK_3_SPLIT]], label [[BLOCK_1]]
; CHECK: block_3.split:
; CHECK-NEXT: [[B_CE:%.*]] = phi i32 [ 0, [[BLOCK_2]] ], [ 1, [[BLOCK_1]] ]
; CHECK-NEXT: br label [[BLOCK_3_EXITSTUB:%.*]]
; CHECK: block_3.exitStub:
; CHECK-NEXT: switch i32 [[TMP1:%.*]], label [[FINAL_BLOCK_0:%.*]] [
; CHECK-NEXT: i32 0, label [[OUTPUT_BLOCK_0_0:%.*]]
; CHECK-NEXT: ]
; CHECK: output_block_0_0:
; CHECK-NEXT: store i32 [[B_CE]], i32* [[TMP0:%.*]], align 4
; CHECK-NEXT: br label [[FINAL_BLOCK_0]]
; CHECK: final_block_0:
; CHECK-NEXT: ret void
;