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[SimplifyCFG] Consider preds to switch in simplifyDuplicateSwitchArms #118955

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Merged
merged 2 commits into from
Dec 13, 2024
Merged

[SimplifyCFG] Consider preds to switch in simplifyDuplicateSwitchArms #118955

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e32c428
[SimplifyCFG] Precommit tests for PR118955 (NFC)
antoniofrighetto Dec 13, 2024
d26df32
[SimplifyCFG] Consider preds to switch in `simplifyDuplicateSwitchArms`
antoniofrighetto Dec 13, 2024
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18 changes: 11 additions & 7 deletions llvm/lib/Transforms/Utils/SimplifyCFG.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -7474,9 +7474,6 @@ static bool simplifySwitchOfCmpIntrinsic(SwitchInst *SI, IRBuilderBase &Builder,
/// IncomingValue and add it in the Wrapper so isEqual can do O(1) checking
/// of the incoming values.
struct SwitchSuccWrapper {
// Keep so we can use SwitchInst::setSuccessor to do the replacement. It won't
// be important to equality though.
unsigned SuccNum;
BasicBlock *Dest;
DenseMap<PHINode *, SmallDenseMap<BasicBlock *, Value *, 8>> *PhiPredIVs;
};
Expand Down Expand Up @@ -7563,6 +7560,7 @@ bool SimplifyCFGOpt::simplifyDuplicateSwitchArms(SwitchInst *SI,
SmallPtrSet<PHINode *, 8> Phis;
SmallPtrSet<BasicBlock *, 8> Seen;
DenseMap<PHINode *, SmallDenseMap<BasicBlock *, Value *, 8>> PhiPredIVs;
DenseMap<BasicBlock *, SmallVector<unsigned, 4>> BBToSuccessorIndexes;
SmallVector<SwitchSuccWrapper> Cases;
Cases.reserve(SI->getNumSuccessors());

Expand All @@ -7575,8 +7573,9 @@ bool SimplifyCFGOpt::simplifyDuplicateSwitchArms(SwitchInst *SI,
continue;

// FIXME: This case needs some extra care because the terminators other than
// SI need to be updated.
if (BB->hasNPredecessorsOrMore(2))
// SI need to be updated. For now, consider only backedges to the SI.
if (BB->hasNPredecessorsOrMore(4) ||
BB->getUniquePredecessor() != SI->getParent())
continue;

// FIXME: Relax that the terminator is a BranchInst by checking for equality
Expand All @@ -7591,8 +7590,11 @@ bool SimplifyCFGOpt::simplifyDuplicateSwitchArms(SwitchInst *SI,
for (BasicBlock *Succ : BI->successors())
for (PHINode &Phi : Succ->phis())
Phis.insert(&Phi);
// Add the successor only if not previously visited.
Cases.emplace_back(SwitchSuccWrapper{BB, &PhiPredIVs});
}
Cases.emplace_back(SwitchSuccWrapper{I, BB, &PhiPredIVs});

BBToSuccessorIndexes[BB].emplace_back(I);
}

// Precompute a data structure to improve performance of isEqual for
Expand Down Expand Up @@ -7627,7 +7629,9 @@ bool SimplifyCFGOpt::simplifyDuplicateSwitchArms(SwitchInst *SI,
// We know that SI's parent BB no longer dominates the old case successor
// since we are making it dead.
Updates.push_back({DominatorTree::Delete, SI->getParent(), SSW.Dest});
SI->setSuccessor(SSW.SuccNum, (*It)->Dest);
const auto &Successors = BBToSuccessorIndexes.at(SSW.Dest);
for (unsigned Idx : Successors)
SI->setSuccessor(Idx, (*It)->Dest);
MadeChange = true;
}
}
Expand Down
34 changes: 21 additions & 13 deletions llvm/test/Transforms/SimplifyCFG/X86/switch_to_lookup_table.ll
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Expand Up @@ -314,20 +314,20 @@ lor.end:
define i32 @overflow(i32 %type) {
; CHECK-LABEL: @overflow(
; CHECK-NEXT: entry:
; CHECK-NEXT: switch i32 [[TYPE:%.*]], label [[IF_END:%.*]] [
; CHECK-NEXT: switch i32 [[TYPE:%.*]], label [[SW_DEFAULT:%.*]] [
; CHECK-NEXT: i32 3, label [[SW_BB3:%.*]]
; CHECK-NEXT: i32 -2147483645, label [[SW_BB3]]
; CHECK-NEXT: i32 1, label [[SW_BB1:%.*]]
; CHECK-NEXT: i32 1, label [[IF_END:%.*]]
; CHECK-NEXT: i32 2, label [[SW_BB2:%.*]]
; CHECK-NEXT: ]
; CHECK: sw.bb1:
; CHECK-NEXT: br label [[IF_END]]
; CHECK: sw.bb2:
; CHECK-NEXT: br label [[IF_END]]
; CHECK: sw.bb3:
; CHECK-NEXT: br label [[IF_END]]
; CHECK: sw.default:
; CHECK-NEXT: br label [[IF_END]]
; CHECK: if.end:
; CHECK-NEXT: [[DIRENT_TYPE_0:%.*]] = phi i32 [ 6, [[SW_BB3]] ], [ 5, [[SW_BB2]] ], [ 0, [[SW_BB1]] ], [ 3, [[ENTRY:%.*]] ]
; CHECK-NEXT: [[DIRENT_TYPE_0:%.*]] = phi i32 [ 3, [[SW_DEFAULT]] ], [ 6, [[SW_BB3]] ], [ 5, [[SW_BB2]] ], [ 0, [[ENTRY:%.*]] ]
; CHECK-NEXT: ret i32 [[DIRENT_TYPE_0]]
;
entry:
Expand All @@ -340,15 +340,23 @@ entry:
i32 3, label %sw.bb3
]

sw.bb: br label %if.end
sw.bb1: br label %if.end
sw.bb2: br label %if.end
sw.bb3: br label %if.end
sw.default: br label %if.end
if.else: br label %if.end
sw.bb: ; preds = %entry, %entry
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@michaelmaitland michaelmaitland Dec 6, 2024

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Did you mean to change these lines?

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@antoniofrighetto antoniofrighetto Dec 10, 2024

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I took the chance to regenerate the test too, as the if.else branch was dead.

br label %if.end

if.end:
%dirent_type.0 = phi i32 [ 3, %sw.default ], [ 6, %sw.bb3 ], [ 5, %sw.bb2 ], [ 0, %sw.bb1 ], [ 3, %sw.bb ], [ 0, %if.else ]
sw.bb1: ; preds = %entry
br label %if.end

sw.bb2: ; preds = %entry
br label %if.end

sw.bb3: ; preds = %entry, %entry
br label %if.end

sw.default: ; preds = %entry
br label %if.end

if.end: ; preds = %sw.default, %sw.bb3, %sw.bb2, %sw.bb1, %sw.bb
%dirent_type.0 = phi i32 [ 3, %sw.default ], [ 6, %sw.bb3 ], [ 5, %sw.bb2 ], [ 0, %sw.bb1 ], [ 3, %sw.bb ]
ret i32 %dirent_type.0
}

Expand Down
72 changes: 72 additions & 0 deletions llvm/test/Transforms/SimplifyCFG/switch-dup-bbs.ll
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Expand Up @@ -127,3 +127,75 @@ define i32 @switch_dup_default(i32 %0, i32 %1, i32 %2, i32 %3) {
%9 = phi i32 [ %3, %5 ], [ %2, %6 ], [ %2, %7 ]
ret i32 %9
}

define i32 @switch_dup_exit(i32 %val) {
; SIMPLIFY-CFG-LABEL: define i32 @switch_dup_exit(
; SIMPLIFY-CFG-SAME: i32 [[VAL:%.*]]) {
; SIMPLIFY-CFG-NEXT: [[ENTRY:.*]]:
; SIMPLIFY-CFG-NEXT: switch i32 [[VAL]], label %[[DEFAULT:.*]] [
; SIMPLIFY-CFG-NEXT: i32 1, label %[[EXIT:.*]]
; SIMPLIFY-CFG-NEXT: i32 11, label %[[EXIT]]
; SIMPLIFY-CFG-NEXT: i32 22, label %[[BB1:.*]]
; SIMPLIFY-CFG-NEXT: ]
; SIMPLIFY-CFG: [[BB1]]:
; SIMPLIFY-CFG-NEXT: br label %[[EXIT]]
; SIMPLIFY-CFG: [[DEFAULT]]:
; SIMPLIFY-CFG-NEXT: br label %[[EXIT]]
; SIMPLIFY-CFG: [[EXIT]]:
; SIMPLIFY-CFG-NEXT: [[RET:%.*]] = phi i32 [ 0, %[[DEFAULT]] ], [ 3, %[[BB1]] ], [ 1, %[[ENTRY]] ], [ 1, %[[ENTRY]] ]
; SIMPLIFY-CFG-NEXT: ret i32 [[RET]]
;
entry:
switch i32 %val, label %default [
i32 1, label %exit
i32 11, label %exit
i32 22, label %bb1
i32 15, label %bb2
i32 0, label %bb2
]

bb1:
br label %exit

bb2:
br label %exit

default:
br label %exit

exit:
%ret = phi i32 [ 0, %default ], [ 0, %bb2 ], [ 3, %bb1 ], [ 1, %entry ], [ 1, %entry ]
ret i32 %ret
}

define i64 @switch_dup_exit_2(i32 %val) {
; SIMPLIFY-CFG-LABEL: define i64 @switch_dup_exit_2(
; SIMPLIFY-CFG-SAME: i32 [[VAL:%.*]]) {
; SIMPLIFY-CFG-NEXT: [[ENTRY:.*:]]
; SIMPLIFY-CFG-NEXT: [[SWITCH_SELECTCMP_CASE1:%.*]] = icmp eq i32 [[VAL]], 1
; SIMPLIFY-CFG-NEXT: [[SWITCH_SELECTCMP_CASE2:%.*]] = icmp eq i32 [[VAL]], 11
; SIMPLIFY-CFG-NEXT: [[SWITCH_SELECTCMP:%.*]] = or i1 [[SWITCH_SELECTCMP_CASE1]], [[SWITCH_SELECTCMP_CASE2]]
; SIMPLIFY-CFG-NEXT: [[RET:%.*]] = select i1 [[SWITCH_SELECTCMP]], i64 1, i64 0
; SIMPLIFY-CFG-NEXT: ret i64 [[RET]]
;
entry:
switch i32 %val, label %default [
i32 1, label %bb2
i32 11, label %exit
i32 13, label %bb1
i32 0, label %bb1
]

bb1:
br label %exit

bb2:
br label %exit

default:
br label %exit

exit:
%ret = phi i64 [ 0, %default ], [ 0, %bb1 ], [ 1, %entry ], [ 1, %bb2 ]
ret i64 %ret
}
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