[llvm] [SimplifyCFG] Consider preds to switch in `simplifyDuplicateSwitchArms` (PR #118955)
Antonio Frighetto via llvm-commits
llvm-commits at lists.llvm.org
Fri Dec 6 03:39:07 PST 2024
https://github.com/antoniofrighetto created https://github.com/llvm/llvm-project/pull/118955
Allow a duplicate basic block with multiple predecessors to the jump table to be simplified, by considering that the same basic block may appear in more switch cases.
>From a0f40686323c566d5c91d7180e722b5d0e489170 Mon Sep 17 00:00:00 2001
From: Antonio Frighetto <me at antoniofrighetto.com>
Date: Fri, 6 Dec 2024 12:11:13 +0100
Subject: [PATCH] [SimplifyCFG] Consider preds to switch in
`simplifyDuplicateSwitchArms`
Allow a duplicate basic block with multiple predecessors to the
jump table to be simplified, by considering that the same basic
block may appear in more switch cases.
---
llvm/lib/Transforms/Utils/SimplifyCFG.cpp | 19 +++++++----
.../SimplifyCFG/X86/switch_to_lookup_table.ll | 34 ++++++++++++-------
.../Transforms/SimplifyCFG/switch-dup-bbs.ll | 32 +++++++++++++++++
3 files changed, 65 insertions(+), 20 deletions(-)
diff --git a/llvm/lib/Transforms/Utils/SimplifyCFG.cpp b/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
index c7e814bced57db..162e60c0c58f7f 100644
--- a/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
+++ b/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
@@ -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;
};
@@ -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());
@@ -7575,8 +7573,10 @@ 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 (pred_size(BB) > 4 || any_of(predecessors(BB), [&](BasicBlock *Pred) {
+ return Pred != SI->getParent();
+ }))
continue;
// FIXME: Relax that the terminator is a BranchInst by checking for equality
@@ -7591,8 +7591,11 @@ 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
@@ -7627,7 +7630,9 @@ 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;
}
}
diff --git a/llvm/test/Transforms/SimplifyCFG/X86/switch_to_lookup_table.ll b/llvm/test/Transforms/SimplifyCFG/X86/switch_to_lookup_table.ll
index 9549ccdbfe9ec4..7f484e2ec29d7d 100644
--- a/llvm/test/Transforms/SimplifyCFG/X86/switch_to_lookup_table.ll
+++ b/llvm/test/Transforms/SimplifyCFG/X86/switch_to_lookup_table.ll
@@ -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:
@@ -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
+ 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
}
diff --git a/llvm/test/Transforms/SimplifyCFG/switch-dup-bbs.ll b/llvm/test/Transforms/SimplifyCFG/switch-dup-bbs.ll
index 0df4deba1a156f..d9590252308e60 100644
--- a/llvm/test/Transforms/SimplifyCFG/switch-dup-bbs.ll
+++ b/llvm/test/Transforms/SimplifyCFG/switch-dup-bbs.ll
@@ -127,3 +127,35 @@ 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 i64 @switch_dup_exit(i32 %val) {
+; SIMPLIFY-CFG-LABEL: define i64 @switch_dup_exit(
+; 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: [[TMP0:%.*]] = select i1 [[SWITCH_SELECTCMP]], i64 1, i64 0
+; SIMPLIFY-CFG-NEXT: ret i64 [[TMP0]]
+;
+entry:
+ switch i32 %val, label %default [
+ i32 1, label %bb2
+ i32 11, label %exit
+ i32 13, label %bb1
+ i32 0, label %bb1
+ ]
+
+bb1: ; preds = %entry, %entry
+ br label %exit
+
+bb2: ; preds = %entry
+ br label %exit
+
+default: ; preds = %entry
+ br label %exit
+
+exit: ; preds = %entry, %default, %bb2, %bb1
+ %ret = phi i64 [ 0, %default ], [ 0, %bb1 ], [ 1, %entry ], [ 1, %bb2 ]
+ ret i64 %ret
+}
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