[llvm] [DFAJumpThreading] Handle select unfolding when user phi is not a dir… (PR #109511)
Usman Nadeem via llvm-commits
llvm-commits at lists.llvm.org
Fri Sep 20 21:25:32 PDT 2024
https://github.com/UsmanNadeem created https://github.com/llvm/llvm-project/pull/109511
…ect successor
Previously the code assumed that the select instruction is defined in a block that is a direct predecessor of the block where the PHINode uses it. So, we were hitting an assertion when we tried to access the def block as an incoming block for the user phi node.
This patch handles that case by using the correct end block and creating a new phi node that aggregates both the values of the select in that end block, and then using that new unfolded phi to overwrite the original user phi node.
Fixes #106083
Change-Id: Ie471994cca232318f74a6e6438efa21e561c2dc0
>From 91de2ece7bad6e73589c47a4b18925e51fbcad1a Mon Sep 17 00:00:00 2001
From: "Nadeem, Usman" <mnadeem at quicinc.com>
Date: Fri, 20 Sep 2024 21:02:18 -0700
Subject: [PATCH] [DFAJumpThreading] Handle select unfolding when user phi is
not a direct successor
Previously the code assumed that the select instruction is defined
in a block that is a direct predecessor of the block where the PHINode
uses it. So, we were hitting an assertion when we tried to access the
def block as an incoming block for the user phi node.
This patch handles that case by using the correct end block
and creating a new phi node that aggregates both the values of the
select in that end block, and then using that new unfolded phi to
overwrite the original user phi node.
Fixes #106083
Change-Id: Ie471994cca232318f74a6e6438efa21e561c2dc0
---
.../Transforms/Scalar/DFAJumpThreading.cpp | 44 ++--
.../dfa-jump-threading-transform.ll | 234 ++++++++++++++++++
2 files changed, 262 insertions(+), 16 deletions(-)
diff --git a/llvm/lib/Transforms/Scalar/DFAJumpThreading.cpp b/llvm/lib/Transforms/Scalar/DFAJumpThreading.cpp
index ef9c264482a640..c80753baf29081 100644
--- a/llvm/lib/Transforms/Scalar/DFAJumpThreading.cpp
+++ b/llvm/lib/Transforms/Scalar/DFAJumpThreading.cpp
@@ -194,7 +194,6 @@ void unfold(DomTreeUpdater *DTU, LoopInfo *LI, SelectInstToUnfold SIToUnfold,
SelectInst *SI = SIToUnfold.getInst();
PHINode *SIUse = SIToUnfold.getUse();
BasicBlock *StartBlock = SI->getParent();
- BasicBlock *EndBlock = SIUse->getParent();
BranchInst *StartBlockTerm =
dyn_cast<BranchInst>(StartBlock->getTerminator());
@@ -202,6 +201,7 @@ void unfold(DomTreeUpdater *DTU, LoopInfo *LI, SelectInstToUnfold SIToUnfold,
assert(SI->hasOneUse());
if (StartBlockTerm->isUnconditional()) {
+ BasicBlock *EndBlock = StartBlock->getUniqueSuccessor();
// Arbitrarily choose the 'false' side for a new input value to the PHI.
BasicBlock *NewBlock = BasicBlock::Create(
SI->getContext(), Twine(SI->getName(), ".si.unfold.false"),
@@ -223,32 +223,44 @@ void unfold(DomTreeUpdater *DTU, LoopInfo *LI, SelectInstToUnfold SIToUnfold,
NewBlock->getFirstInsertionPt());
NewPhi->addIncoming(SIOp2, StartBlock);
- if (auto *OpSi = dyn_cast<SelectInst>(SIOp1))
- NewSIsToUnfold->push_back(SelectInstToUnfold(OpSi, SIUse));
- if (auto *OpSi = dyn_cast<SelectInst>(SIOp2))
- NewSIsToUnfold->push_back(SelectInstToUnfold(OpSi, NewPhi));
+ // Update any other PHI nodes in EndBlock.
+ for (PHINode &Phi : EndBlock->phis()) {
+ if (SIUse == &Phi)
+ continue;
+ Phi.addIncoming(Phi.getIncomingValueForBlock(StartBlock), NewBlock);
+ }
// Update the phi node of SI.
- for (unsigned Idx = 0; Idx < SIUse->getNumIncomingValues(); ++Idx) {
- if (SIUse->getIncomingBlock(Idx) == StartBlock)
- SIUse->setIncomingValue(Idx, SIOp1);
- }
- SIUse->addIncoming(NewPhi, NewBlock);
+ if (EndBlock == SIUse->getParent()) {
+ SIUse->setIncomingValueForBlock(StartBlock, SIOp1);
+ SIUse->addIncoming(NewPhi, NewBlock);
+ } else {
+ PHINode *EndPhi = PHINode::Create(SIUse->getType(), pred_size(EndBlock),
+ Twine(SI->getName(), ".si.unfold.phi"),
+ EndBlock->getFirstInsertionPt());
+ for (BasicBlock *Pred : predecessors(EndBlock)) {
+ if (Pred != StartBlock && Pred != NewBlock)
+ EndPhi->addIncoming(EndPhi, Pred);
+ }
- // Update any other PHI nodes in EndBlock.
- for (auto II = EndBlock->begin(); PHINode *Phi = dyn_cast<PHINode>(II);
- ++II) {
- if (Phi != SIUse)
- Phi->addIncoming(Phi->getIncomingValueForBlock(StartBlock), NewBlock);
+ EndPhi->addIncoming(SIOp1, StartBlock);
+ EndPhi->addIncoming(NewPhi, NewBlock);
+ SIUse->replaceUsesOfWith(SI, EndPhi);
+ SIUse = EndPhi;
}
- StartBlockTerm->eraseFromParent();
+ if (auto *OpSi = dyn_cast<SelectInst>(SIOp1))
+ NewSIsToUnfold->push_back(SelectInstToUnfold(OpSi, SIUse));
+ if (auto *OpSi = dyn_cast<SelectInst>(SIOp2))
+ NewSIsToUnfold->push_back(SelectInstToUnfold(OpSi, NewPhi));
// Insert the real conditional branch based on the original condition.
+ StartBlockTerm->eraseFromParent();
BranchInst::Create(EndBlock, NewBlock, SI->getCondition(), StartBlock);
DTU->applyUpdates({{DominatorTree::Insert, StartBlock, EndBlock},
{DominatorTree::Insert, StartBlock, NewBlock}});
} else {
+ BasicBlock *EndBlock = SIUse->getParent();
BasicBlock *NewBlockT = BasicBlock::Create(
SI->getContext(), Twine(SI->getName(), ".si.unfold.true"),
EndBlock->getParent(), EndBlock);
diff --git a/llvm/test/Transforms/DFAJumpThreading/dfa-jump-threading-transform.ll b/llvm/test/Transforms/DFAJumpThreading/dfa-jump-threading-transform.ll
index c38f81d0f046ef..b48e10e8d2a96c 100644
--- a/llvm/test/Transforms/DFAJumpThreading/dfa-jump-threading-transform.ll
+++ b/llvm/test/Transforms/DFAJumpThreading/dfa-jump-threading-transform.ll
@@ -300,3 +300,237 @@ define void @self-reference() {
end:
ret void
}
+
+ at a = external dso_local global ptr, align 8
+ at b = external dso_local global i32, align 4
+ at c = external dso_local global i64, align 8
+ at d = external dso_local global i16, align 2
+ at e = external dso_local global i64, align 8
+ at f = external dso_local global i32, align 4
+ at g = external dso_local global i64, align 8
+ at h = external dso_local global i32, align 4
+ at i = external dso_local global ptr, align 8
+
+define void @pr106083_invalidBBarg_fold() {
+; CHECK-LABEL: @pr106083_invalidBBarg_fold(
+; CHECK-NEXT: [[TMP1:%.*]] = load i32, ptr @h, align 4
+; CHECK-NEXT: [[DOTNOT2:%.*]] = icmp eq i32 [[TMP1]], 0
+; CHECK-NEXT: [[D_PROMOTED3:%.*]] = load i16, ptr @d, align 1
+; CHECK-NEXT: br i1 [[DOTNOT2]], label [[BB0:%.*]], label [[DOT_SI_UNFOLD_FALSE:%.*]]
+; CHECK: BB0.loopexit:
+; CHECK-NEXT: [[D_PROMOTED41:%.*]] = phi i16 [ [[D_PROMOTED4_JT2:%.*]], [[BB7_JT2:%.*]] ], [ [[D_PROMOTED4:%.*]], [[BB7:%.*]] ]
+; CHECK-NEXT: br label [[BB0]]
+; CHECK: ..si.unfold.false:
+; CHECK-NEXT: [[DOTSI_UNFOLD_PHI:%.*]] = phi i32 [ 6, [[TMP0:%.*]] ]
+; CHECK-NEXT: br label [[BB0]]
+; CHECK: BB0:
+; CHECK-NEXT: [[D_PROMOTED6:%.*]] = phi i16 [ [[D_PROMOTED3]], [[TMP0]] ], [ [[D_PROMOTED41]], [[BB0_LOOPEXIT:%.*]] ], [ [[D_PROMOTED3]], [[DOT_SI_UNFOLD_FALSE]] ]
+; CHECK-NEXT: [[DOT_SI_UNFOLD_PHI:%.*]] = phi i32 [ [[DOT_SI_UNFOLD_PHI]], [[BB0_LOOPEXIT]] ], [ 0, [[TMP0]] ], [ [[DOTSI_UNFOLD_PHI]], [[DOT_SI_UNFOLD_FALSE]] ]
+; CHECK-NEXT: br label [[BB1_JT2:%.*]]
+; CHECK: BB1:
+; CHECK-NEXT: [[D_PROMOTED5:%.*]] = phi i16 [ [[D_PROMOTED4]], [[BB1_BACKEDGE:%.*]] ]
+; CHECK-NEXT: [[TMP2:%.*]] = phi i16 [ [[TMP10:%.*]], [[BB1_BACKEDGE]] ]
+; CHECK-NEXT: [[DOT1:%.*]] = phi i32 [ [[DOT3:%.*]], [[BB1_BACKEDGE]] ]
+; CHECK-NEXT: [[TMP3:%.*]] = load volatile i32, ptr @f, align 4
+; CHECK-NEXT: [[DOTNOT:%.*]] = icmp eq i32 [[TMP3]], 0
+; CHECK-NEXT: br i1 [[DOTNOT]], label [[BB7]], label [[BB2:%.*]]
+; CHECK: BB1.jt2:
+; CHECK-NEXT: [[D_PROMOTED5_JT2:%.*]] = phi i16 [ [[D_PROMOTED6]], [[BB0]] ]
+; CHECK-NEXT: [[TMP4:%.*]] = phi i16 [ [[D_PROMOTED6]], [[BB0]] ]
+; CHECK-NEXT: [[DOT1_JT2:%.*]] = phi i32 [ 2, [[BB0]] ]
+; CHECK-NEXT: [[TMP5:%.*]] = load volatile i32, ptr @f, align 4
+; CHECK-NEXT: [[DOTNOT_JT2:%.*]] = icmp eq i32 [[TMP5]], 0
+; CHECK-NEXT: br i1 [[DOTNOT_JT2]], label [[BB7_JT2]], label [[BB2_JT2:%.*]]
+; CHECK: BB2:
+; CHECK-NEXT: [[TMP6:%.*]] = add i16 [[TMP2]], 1
+; CHECK-NEXT: store i16 [[TMP6]], ptr @d, align 2
+; CHECK-NEXT: [[TMP7:%.*]] = load volatile i64, ptr @g, align 8
+; CHECK-NEXT: [[DOTNOT1:%.*]] = icmp eq i64 [[TMP7]], 0
+; CHECK-NEXT: br i1 [[DOTNOT1]], label [[BB7]], label [[SPEC_SELECT_SI_UNFOLD_FALSE:%.*]]
+; CHECK: BB2.jt2:
+; CHECK-NEXT: [[TMP8:%.*]] = add i16 [[TMP4]], 1
+; CHECK-NEXT: store i16 [[TMP8]], ptr @d, align 2
+; CHECK-NEXT: [[TMP9:%.*]] = load volatile i64, ptr @g, align 8
+; CHECK-NEXT: [[DOTNOT1_JT2:%.*]] = icmp eq i64 [[TMP9]], 0
+; CHECK-NEXT: br i1 [[DOTNOT1_JT2]], label [[BB7]], label [[SPEC_SELECT_SI_UNFOLD_FALSE_JT2:%.*]]
+; CHECK: spec.select.si.unfold.false:
+; CHECK-NEXT: [[DOT1_SI_UNFOLD_PHI:%.*]] = phi i32 [ [[DOT1]], [[BB2]] ]
+; CHECK-NEXT: br label [[BB7]]
+; CHECK: spec.select.si.unfold.false.jt2:
+; CHECK-NEXT: [[DOT1_SI_UNFOLD_PHI_JT2:%.*]] = phi i32 [ [[DOT1_JT2]], [[BB2_JT2]] ]
+; CHECK-NEXT: br label [[BB7_JT2]]
+; CHECK: BB7:
+; CHECK-NEXT: [[D_PROMOTED4]] = phi i16 [ [[D_PROMOTED5]], [[BB1:%.*]] ], [ [[TMP6]], [[BB2]] ], [ [[TMP6]], [[SPEC_SELECT_SI_UNFOLD_FALSE]] ], [ [[TMP8]], [[BB2_JT2]] ]
+; CHECK-NEXT: [[TMP10]] = phi i16 [ [[TMP2]], [[BB1]] ], [ [[TMP6]], [[BB2]] ], [ [[TMP6]], [[SPEC_SELECT_SI_UNFOLD_FALSE]] ], [ [[TMP8]], [[BB2_JT2]] ]
+; CHECK-NEXT: [[DOT3]] = phi i32 [ [[DOT1]], [[BB1]] ], [ [[DOT_SI_UNFOLD_PHI]], [[BB2]] ], [ [[DOT1_SI_UNFOLD_PHI]], [[SPEC_SELECT_SI_UNFOLD_FALSE]] ], [ [[DOT_SI_UNFOLD_PHI]], [[BB2_JT2]] ]
+; CHECK-NEXT: switch i32 [[DOT3]], label [[BB9:%.*]] [
+; CHECK-NEXT: i32 0, label [[BB1_BACKEDGE]]
+; CHECK-NEXT: i32 7, label [[BB1_BACKEDGE]]
+; CHECK-NEXT: i32 6, label [[BB8:%.*]]
+; CHECK-NEXT: i32 2, label [[BB0_LOOPEXIT]]
+; CHECK-NEXT: ]
+; CHECK: BB7.jt2:
+; CHECK-NEXT: [[D_PROMOTED4_JT2]] = phi i16 [ [[D_PROMOTED5_JT2]], [[BB1_JT2]] ], [ [[TMP8]], [[SPEC_SELECT_SI_UNFOLD_FALSE_JT2]] ]
+; CHECK-NEXT: [[TMP11:%.*]] = phi i16 [ [[TMP4]], [[BB1_JT2]] ], [ [[TMP8]], [[SPEC_SELECT_SI_UNFOLD_FALSE_JT2]] ]
+; CHECK-NEXT: [[DOT3_JT2:%.*]] = phi i32 [ [[DOT1_JT2]], [[BB1_JT2]] ], [ [[DOT1_SI_UNFOLD_PHI_JT2]], [[SPEC_SELECT_SI_UNFOLD_FALSE_JT2]] ]
+; CHECK-NEXT: br label [[BB0_LOOPEXIT]]
+; CHECK: BB1.backedge:
+; CHECK-NEXT: br label [[BB1]]
+; CHECK: BB8:
+; CHECK-NEXT: ret void
+; CHECK: BB9:
+; CHECK-NEXT: unreachable
+;
+ %1 = load i32, ptr @h, align 4
+ %.not2 = icmp eq i32 %1, 0
+ %. = select i1 %.not2, i32 0, i32 6
+ %d.promoted3 = load i16, ptr @d, align 1
+ br label %BB0
+
+BB0.loopexit: ; preds = %BB7
+ br label %BB0
+
+BB0: ; preds = %BB0.loopexit, %0
+ %d.promoted6 = phi i16 [ %d.promoted3, %0 ], [ %d.promoted4, %BB0.loopexit ]
+ br label %BB1
+
+BB1: ; preds = %BB1.backedge, %BB0
+ %d.promoted5 = phi i16 [ %d.promoted6, %BB0 ], [ %d.promoted4, %BB1.backedge ]
+ %2 = phi i16 [ %d.promoted6, %BB0 ], [ %6, %BB1.backedge ]
+ %.1 = phi i32 [ 2, %BB0 ], [ %.3, %BB1.backedge ]
+ %3 = load volatile i32, ptr @f, align 4
+ %.not = icmp eq i32 %3, 0
+ br i1 %.not, label %BB7, label %BB2
+
+BB2: ; preds = %BB1
+ %4 = add i16 %2, 1
+ store i16 %4, ptr @d, align 2
+ %5 = load volatile i64, ptr @g, align 8
+ %.not1 = icmp eq i64 %5, 0
+ %spec.select = select i1 %.not1, i32 %., i32 %.1
+ br label %BB7
+
+BB7: ; preds = %BB2, %BB1
+ %d.promoted4 = phi i16 [ %d.promoted5, %BB1 ], [ %4, %BB2 ]
+ %6 = phi i16 [ %2, %BB1 ], [ %4, %BB2 ]
+ %.3 = phi i32 [ %.1, %BB1 ], [ %spec.select, %BB2 ]
+ switch i32 %.3, label %BB9 [
+ i32 0, label %BB1.backedge
+ i32 7, label %BB1.backedge
+ i32 6, label %BB8
+ i32 2, label %BB0.loopexit
+ ]
+
+BB1.backedge: ; preds = %BB7, %BB7
+ br label %BB1
+
+BB8: ; preds = %BB7
+ ret void
+
+BB9: ; preds = %BB7
+ unreachable
+}
+
+
+define void @pr106083_select_dead_uses() {
+; CHECK-LABEL: @pr106083_select_dead_uses(
+; CHECK-NEXT: [[TMP1:%.*]] = load ptr, ptr @a, align 8
+; CHECK-NEXT: [[TMP2:%.*]] = load ptr, ptr @i, align 8
+; CHECK-NEXT: [[TMP3:%.*]] = load i64, ptr @c, align 8
+; CHECK-NEXT: [[DOTNOT3:%.*]] = icmp eq i64 [[TMP3]], 0
+; CHECK-NEXT: br i1 [[DOTNOT3]], label [[DOTLOOPEXIT6:%.*]], label [[SPEC_SELECT_SI_UNFOLD_FALSE:%.*]]
+; CHECK: .loopexit6.loopexit:
+; CHECK-NEXT: br label [[DOTLOOPEXIT6]]
+; CHECK: spec.select.si.unfold.false:
+; CHECK-NEXT: [[DOTSI_UNFOLD_PHI:%.*]] = phi i32 [ 2, [[TMP0:%.*]] ]
+; CHECK-NEXT: br label [[DOTLOOPEXIT6]]
+; CHECK: .loopexit6:
+; CHECK-NEXT: [[SPEC_SELECT_SI_UNFOLD_PHI:%.*]] = phi i32 [ [[SPEC_SELECT_SI_UNFOLD_PHI]], [[DOTLOOPEXIT6_LOOPEXIT:%.*]] ], [ 0, [[TMP0]] ], [ [[DOTSI_UNFOLD_PHI]], [[SPEC_SELECT_SI_UNFOLD_FALSE]] ]
+; CHECK-NEXT: br label [[TMP6:%.*]]
+; CHECK: 4:
+; CHECK-NEXT: [[DOT1:%.*]] = phi i32 [ [[DOT21:%.*]], [[DOTBACKEDGE:%.*]] ]
+; CHECK-NEXT: [[TMP5:%.*]] = load i32, ptr [[TMP1]], align 4
+; CHECK-NEXT: [[DOTNOT:%.*]] = icmp eq i32 [[TMP5]], 0
+; CHECK-NEXT: br i1 [[DOTNOT]], label [[SELECT_UNFOLD_JT0:%.*]], label [[TMP8:%.*]]
+; CHECK: 6:
+; CHECK-NEXT: [[DOT1_JT2:%.*]] = phi i32 [ 2, [[DOTLOOPEXIT6]] ]
+; CHECK-NEXT: [[TMP7:%.*]] = load i32, ptr [[TMP1]], align 4
+; CHECK-NEXT: [[DOTNOT_JT2:%.*]] = icmp eq i32 [[TMP7]], 0
+; CHECK-NEXT: br i1 [[DOTNOT_JT2]], label [[SELECT_UNFOLD_JT0]], label [[TMP10:%.*]]
+; CHECK: 8:
+; CHECK-NEXT: [[TMP9:%.*]] = load i32, ptr [[TMP2]], align 4
+; CHECK-NEXT: [[DOTNOT2:%.*]] = icmp eq i32 [[TMP9]], 0
+; CHECK-NEXT: br i1 [[DOTNOT2]], label [[SELECT_UNFOLD:%.*]], label [[SPEC_SELECT7_SI_UNFOLD_FALSE:%.*]]
+; CHECK: 10:
+; CHECK-NEXT: [[TMP11:%.*]] = load i32, ptr [[TMP2]], align 4
+; CHECK-NEXT: [[DOTNOT2_JT2:%.*]] = icmp eq i32 [[TMP11]], 0
+; CHECK-NEXT: br i1 [[DOTNOT2_JT2]], label [[SELECT_UNFOLD]], label [[SPEC_SELECT7_SI_UNFOLD_FALSE_JT2:%.*]]
+; CHECK: spec.select7.si.unfold.false:
+; CHECK-NEXT: [[DOT1_SI_UNFOLD_PHI:%.*]] = phi i32 [ [[DOT1]], [[TMP8]] ]
+; CHECK-NEXT: br label [[SELECT_UNFOLD]]
+; CHECK: spec.select7.si.unfold.false.jt2:
+; CHECK-NEXT: [[DOT1_SI_UNFOLD_PHI_JT2:%.*]] = phi i32 [ [[DOT1_JT2]], [[TMP10]] ]
+; CHECK-NEXT: br label [[SELECT_UNFOLD_JT2:%.*]]
+; CHECK: select.unfold:
+; CHECK-NEXT: [[DOT2:%.*]] = phi i32 [ [[SPEC_SELECT_SI_UNFOLD_PHI]], [[TMP8]] ], [ [[DOT1_SI_UNFOLD_PHI]], [[SPEC_SELECT7_SI_UNFOLD_FALSE]] ], [ [[SPEC_SELECT_SI_UNFOLD_PHI]], [[TMP10]] ]
+; CHECK-NEXT: switch i32 [[DOT2]], label [[TMP12:%.*]] [
+; CHECK-NEXT: i32 0, label [[DOTPREHEADER_PREHEADER:%.*]]
+; CHECK-NEXT: i32 2, label [[DOTLOOPEXIT6_LOOPEXIT]]
+; CHECK-NEXT: ]
+; CHECK: select.unfold.jt2:
+; CHECK-NEXT: [[DOT2_JT2:%.*]] = phi i32 [ [[DOT1_SI_UNFOLD_PHI_JT2]], [[SPEC_SELECT7_SI_UNFOLD_FALSE_JT2]] ]
+; CHECK-NEXT: br label [[DOTLOOPEXIT6_LOOPEXIT]]
+; CHECK: select.unfold.jt0:
+; CHECK-NEXT: [[DOT2_JT0:%.*]] = phi i32 [ 0, [[TMP4:%.*]] ], [ 0, [[TMP6]] ]
+; CHECK-NEXT: br label [[DOTPREHEADER_PREHEADER]]
+; CHECK: .preheader.preheader:
+; CHECK-NEXT: [[DOT21]] = phi i32 [ [[DOT2_JT0]], [[SELECT_UNFOLD_JT0]] ], [ [[DOT2]], [[SELECT_UNFOLD]] ]
+; CHECK-NEXT: store i32 0, ptr @b, align 4
+; CHECK-NEXT: br label [[DOTBACKEDGE]]
+; CHECK: .backedge:
+; CHECK-NEXT: br label [[TMP4]]
+; CHECK: 12:
+; CHECK-NEXT: unreachable
+;
+ %1 = load ptr, ptr @a, align 8
+ %2 = load ptr, ptr @i, align 8
+ %3 = load i64, ptr @c, align 8
+ %.not3 = icmp eq i64 %3, 0
+ %spec.select = select i1 %.not3, i32 0, i32 2
+ br label %.loopexit6
+
+.loopexit6.loopexit: ; preds = %select.unfold
+ br label %.loopexit6
+
+.loopexit6: ; preds = %.loopexit6.loopexit, %0
+ br label %4
+
+4: ; preds = %.backedge, %.loopexit6
+ %.1 = phi i32 [ 2, %.loopexit6 ], [ %.2, %.backedge ]
+ %5 = load i32, ptr %1, align 4
+ %.not = icmp eq i32 %5, 0
+ br i1 %.not, label %select.unfold, label %6
+
+6: ; preds = %4
+ %7 = load i32, ptr %2, align 4
+ %.not2 = icmp eq i32 %7, 0
+ %spec.select7 = select i1 %.not2, i32 %spec.select, i32 %.1
+ br label %select.unfold
+
+select.unfold: ; preds = %6, %4
+ %.2 = phi i32 [ 0, %4 ], [ %spec.select7, %6 ]
+ switch i32 %.2, label %8 [
+ i32 0, label %.preheader.preheader
+ i32 2, label %.loopexit6.loopexit
+ ]
+
+.preheader.preheader: ; preds = %select.unfold
+ store i32 0, ptr @b, align 4
+ br label %.backedge
+
+.backedge: ; preds = %.preheader.preheader
+ br label %4
+
+8: ; preds = %select.unfold
+ unreachable
+}
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