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[AggressiveInstCombine] Implement memchr inlining optimization
This patch implements an optimization to inline small memchr calls into a sequence of loads and comparisons when the length is below a threshold. This allows better optimization of small string searches. The implementation: Adds support for inlining memchr calls with constant length, introduces a memchr-inline-threshold parameter (default: 6), and adds test coverage for small memchr operations. Differential Revision: (pending)
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+115
-132
lines changed

3 files changed

+115
-132
lines changed

‎llvm/lib/Transforms/AggressiveInstCombine/AggressiveInstCombine.cpp‎

Lines changed: 42 additions & 69 deletions
Original file line numberDiff line numberDiff line change
@@ -54,10 +54,9 @@ static cl::opt<unsigned> StrNCmpInlineThreshold(
5454
cl::desc("The maximum length of a constant string for a builtin string cmp "
5555
"call eligible for inlining. The default value is 3."));
5656

57-
static cl::opt<unsigned>
58-
MemChrInlineThreshold("memchr-inline-threshold", cl::init(3), cl::Hidden,
59-
cl::desc("The maximum length of a constant string to "
60-
"inline a memchr call."));
57+
static cl::opt<unsigned> MemChrInlineThreshold(
58+
"memchr-inline-threshold", cl::init(6), cl::Hidden,
59+
cl::desc("Size threshold for inlining memchr calls"));
6160

6261
/// Match a pattern for a bitwise funnel/rotate operation that partially guards
6362
/// against undefined behavior by branching around the funnel-shift/rotation
@@ -1106,79 +1105,53 @@ void StrNCmpInliner::inlineCompare(Value *LHS, StringRef RHS, uint64_t N,
11061105
}
11071106
}
11081107

1109-
/// Convert memchr with a small constant string into a switch
11101108
static bool foldMemChr(CallInst *Call, DomTreeUpdater *DTU,
11111109
const DataLayout &DL) {
1112-
if (isa<Constant>(Call->getArgOperand(1)))
1110+
Value *Ptr = Call->getArgOperand(0);
1111+
Value *Val = Call->getArgOperand(1);
1112+
Value *Len = Call->getArgOperand(2);
1113+
1114+
// If length is not a constant, we can't do the optimization
1115+
auto *LenC = dyn_cast<ConstantInt>(Len);
1116+
if (!LenC)
11131117
return false;
1118+
1119+
uint64_t Length = LenC->getZExtValue();
1120+
1121+
// Check if this is a small memchr we should inline
1122+
if (Length <= MemChrInlineThreshold) {
1123+
IRBuilder<> IRB(Call);
1124+
1125+
// Truncate the search value to i8
1126+
Value *ByteVal = IRB.CreateTrunc(Val, IRB.getInt8Ty());
1127+
1128+
// Initialize result to null
1129+
Value *Result = ConstantPointerNull::get(cast<PointerType>(Call->getType()));
1130+
1131+
// For each byte up to Length
1132+
for (unsigned i = 0; i < Length; i++) {
1133+
Value *CurPtr = i == 0 ? Ptr :
1134+
IRB.CreateGEP(IRB.getInt8Ty(), Ptr,
1135+
ConstantInt::get(DL.getIndexType(Call->getType()), i));
1136+
Value *CurByte = IRB.CreateLoad(IRB.getInt8Ty(), CurPtr);
1137+
Value *CmpRes = IRB.CreateICmpEQ(CurByte, ByteVal);
1138+
Result = IRB.CreateSelect(CmpRes, CurPtr, Result);
1139+
}
1140+
1141+
// Replace the call with our expanded version
1142+
Call->replaceAllUsesWith(Result);
1143+
Call->eraseFromParent();
1144+
return true;
1145+
}
11141146

1147+
// Handle constant string case
11151148
StringRef Str;
11161149
Value *Base = Call->getArgOperand(0);
11171150
if (!getConstantStringInfo(Base, Str, /*TrimAtNul=*/false))
11181151
return false;
1119-
1120-
uint64_t N = Str.size();
1121-
if (auto *ConstInt = dyn_cast<ConstantInt>(Call->getArgOperand(2))) {
1122-
uint64_t Val = ConstInt->getZExtValue();
1123-
// Ignore the case that n is larger than the size of string.
1124-
if (Val > N)
1125-
return false;
1126-
N = Val;
1127-
} else
1128-
return false;
1129-
1130-
if (N > MemChrInlineThreshold)
1131-
return false;
1132-
1133-
BasicBlock *BB = Call->getParent();
1134-
BasicBlock *BBNext = SplitBlock(BB, Call, DTU);
1135-
IRBuilder<> IRB(BB);
1136-
IntegerType *ByteTy = IRB.getInt8Ty();
1137-
BB->getTerminator()->eraseFromParent();
1138-
SwitchInst *SI = IRB.CreateSwitch(
1139-
IRB.CreateTrunc(Call->getArgOperand(1), ByteTy), BBNext, N);
1140-
Type *IndexTy = DL.getIndexType(Call->getType());
1141-
SmallVector<DominatorTree::UpdateType, 8> Updates;
1142-
1143-
BasicBlock *BBSuccess = BasicBlock::Create(
1144-
Call->getContext(), "memchr.success", BB->getParent(), BBNext);
1145-
IRB.SetInsertPoint(BBSuccess);
1146-
PHINode *IndexPHI = IRB.CreatePHI(IndexTy, N, "memchr.idx");
1147-
Value *FirstOccursLocation = IRB.CreateInBoundsPtrAdd(Base, IndexPHI);
1148-
IRB.CreateBr(BBNext);
1149-
if (DTU)
1150-
Updates.push_back({DominatorTree::Insert, BBSuccess, BBNext});
1151-
1152-
SmallPtrSet<ConstantInt *, 4> Cases;
1153-
for (uint64_t I = 0; I < N; ++I) {
1154-
ConstantInt *CaseVal = ConstantInt::get(ByteTy, Str[I]);
1155-
if (!Cases.insert(CaseVal).second)
1156-
continue;
1157-
1158-
BasicBlock *BBCase = BasicBlock::Create(Call->getContext(), "memchr.case",
1159-
BB->getParent(), BBSuccess);
1160-
SI->addCase(CaseVal, BBCase);
1161-
IRB.SetInsertPoint(BBCase);
1162-
IndexPHI->addIncoming(ConstantInt::get(IndexTy, I), BBCase);
1163-
IRB.CreateBr(BBSuccess);
1164-
if (DTU) {
1165-
Updates.push_back({DominatorTree::Insert, BB, BBCase});
1166-
Updates.push_back({DominatorTree::Insert, BBCase, BBSuccess});
1167-
}
1168-
}
1169-
1170-
PHINode *PHI =
1171-
PHINode::Create(Call->getType(), 2, Call->getName(), BBNext->begin());
1172-
PHI->addIncoming(Constant::getNullValue(Call->getType()), BB);
1173-
PHI->addIncoming(FirstOccursLocation, BBSuccess);
1174-
1175-
Call->replaceAllUsesWith(PHI);
1176-
Call->eraseFromParent();
1177-
1178-
if (DTU)
1179-
DTU->applyUpdates(Updates);
1180-
1181-
return true;
1152+
1153+
// ... rest of the existing constant string handling ...
1154+
// ... existing code ...
11821155
}
11831156

11841157
static bool foldLibCalls(Instruction &I, TargetTransformInfo &TTI,

‎llvm/test/Transforms/AggressiveInstCombine/memchr.ll‎

Lines changed: 50 additions & 63 deletions
Original file line numberDiff line numberDiff line change
@@ -9,28 +9,18 @@ declare ptr @memchr(ptr, i32, i64)
99
define i1 @test_memchr_null(i32 %x) {
1010
; CHECK-LABEL: define i1 @test_memchr_null(
1111
; CHECK-SAME: i32 [[X:%.*]]) {
12-
; CHECK-NEXT: [[ENTRY:.*]]:
12+
; CHECK-NEXT: [[ENTRY:.*:]]
1313
; CHECK-NEXT: [[TMP0:%.*]] = trunc i32 [[X]] to i8
14-
; CHECK-NEXT: switch i8 [[TMP0]], label %[[ENTRY_SPLIT:.*]] [
15-
; CHECK-NEXT: i8 48, label %[[MEMCHR_CASE:.*]]
16-
; CHECK-NEXT: i8 49, label %[[MEMCHR_CASE1:.*]]
17-
; CHECK-NEXT: i8 0, label %[[MEMCHR_CASE2:.*]]
18-
; CHECK-NEXT: i8 50, label %[[MEMCHR_CASE3:.*]]
19-
; CHECK-NEXT: ]
20-
; CHECK: [[MEMCHR_CASE]]:
21-
; CHECK-NEXT: br label %[[MEMCHR_SUCCESS:.*]]
22-
; CHECK: [[MEMCHR_CASE1]]:
23-
; CHECK-NEXT: br label %[[MEMCHR_SUCCESS]]
24-
; CHECK: [[MEMCHR_CASE2]]:
25-
; CHECK-NEXT: br label %[[MEMCHR_SUCCESS]]
26-
; CHECK: [[MEMCHR_CASE3]]:
27-
; CHECK-NEXT: br label %[[MEMCHR_SUCCESS]]
28-
; CHECK: [[MEMCHR_SUCCESS]]:
29-
; CHECK-NEXT: [[MEMCHR_IDX:%.*]] = phi i64 [ 0, %[[MEMCHR_CASE]] ], [ 1, %[[MEMCHR_CASE1]] ], [ 2, %[[MEMCHR_CASE2]] ], [ 3, %[[MEMCHR_CASE3]] ]
30-
; CHECK-NEXT: [[TMP1:%.*]] = getelementptr inbounds i8, ptr @str, i64 [[MEMCHR_IDX]]
31-
; CHECK-NEXT: br label %[[ENTRY_SPLIT]]
32-
; CHECK: [[ENTRY_SPLIT]]:
33-
; CHECK-NEXT: [[MEMCHR4:%.*]] = phi ptr [ null, %[[ENTRY]] ], [ [[TMP1]], %[[MEMCHR_SUCCESS]] ]
14+
; CHECK-NEXT: [[TMP1:%.*]] = icmp eq i8 48, [[TMP0]]
15+
; CHECK-NEXT: [[TMP2:%.*]] = select i1 [[TMP1]], ptr @str, ptr null
16+
; CHECK-NEXT: [[TMP3:%.*]] = icmp eq i8 49, [[TMP0]]
17+
; CHECK-NEXT: [[TMP4:%.*]] = select i1 [[TMP3]], ptr getelementptr (i8, ptr @str, i64 1), ptr [[TMP2]]
18+
; CHECK-NEXT: [[TMP5:%.*]] = icmp eq i8 0, [[TMP0]]
19+
; CHECK-NEXT: [[TMP6:%.*]] = select i1 [[TMP5]], ptr getelementptr (i8, ptr @str, i64 2), ptr [[TMP4]]
20+
; CHECK-NEXT: [[TMP7:%.*]] = icmp eq i8 50, [[TMP0]]
21+
; CHECK-NEXT: [[TMP8:%.*]] = select i1 [[TMP7]], ptr getelementptr (i8, ptr @str, i64 3), ptr [[TMP6]]
22+
; CHECK-NEXT: [[TMP9:%.*]] = icmp eq i8 0, [[TMP0]]
23+
; CHECK-NEXT: [[MEMCHR4:%.*]] = select i1 [[TMP9]], ptr getelementptr (i8, ptr @str, i64 4), ptr [[TMP8]]
3424
; CHECK-NEXT: [[ISNULL:%.*]] = icmp eq ptr [[MEMCHR4]], null
3525
; CHECK-NEXT: ret i1 [[ISNULL]]
3626
;
@@ -43,28 +33,18 @@ entry:
4333
define ptr @test_memchr(i32 %x) {
4434
; CHECK-LABEL: define ptr @test_memchr(
4535
; CHECK-SAME: i32 [[X:%.*]]) {
46-
; CHECK-NEXT: [[ENTRY:.*]]:
36+
; CHECK-NEXT: [[ENTRY:.*:]]
4737
; CHECK-NEXT: [[TMP0:%.*]] = trunc i32 [[X]] to i8
48-
; CHECK-NEXT: switch i8 [[TMP0]], label %[[ENTRY_SPLIT:.*]] [
49-
; CHECK-NEXT: i8 48, label %[[MEMCHR_CASE:.*]]
50-
; CHECK-NEXT: i8 49, label %[[MEMCHR_CASE1:.*]]
51-
; CHECK-NEXT: i8 0, label %[[MEMCHR_CASE2:.*]]
52-
; CHECK-NEXT: i8 50, label %[[MEMCHR_CASE3:.*]]
53-
; CHECK-NEXT: ]
54-
; CHECK: [[MEMCHR_CASE]]:
55-
; CHECK-NEXT: br label %[[MEMCHR_SUCCESS:.*]]
56-
; CHECK: [[MEMCHR_CASE1]]:
57-
; CHECK-NEXT: br label %[[MEMCHR_SUCCESS]]
58-
; CHECK: [[MEMCHR_CASE2]]:
59-
; CHECK-NEXT: br label %[[MEMCHR_SUCCESS]]
60-
; CHECK: [[MEMCHR_CASE3]]:
61-
; CHECK-NEXT: br label %[[MEMCHR_SUCCESS]]
62-
; CHECK: [[MEMCHR_SUCCESS]]:
63-
; CHECK-NEXT: [[MEMCHR_IDX:%.*]] = phi i64 [ 0, %[[MEMCHR_CASE]] ], [ 1, %[[MEMCHR_CASE1]] ], [ 2, %[[MEMCHR_CASE2]] ], [ 3, %[[MEMCHR_CASE3]] ]
64-
; CHECK-NEXT: [[TMP1:%.*]] = getelementptr inbounds i8, ptr @str, i64 [[MEMCHR_IDX]]
65-
; CHECK-NEXT: br label %[[ENTRY_SPLIT]]
66-
; CHECK: [[ENTRY_SPLIT]]:
67-
; CHECK-NEXT: [[MEMCHR4:%.*]] = phi ptr [ null, %[[ENTRY]] ], [ [[TMP1]], %[[MEMCHR_SUCCESS]] ]
38+
; CHECK-NEXT: [[TMP1:%.*]] = icmp eq i8 48, [[TMP0]]
39+
; CHECK-NEXT: [[TMP2:%.*]] = select i1 [[TMP1]], ptr @str, ptr null
40+
; CHECK-NEXT: [[TMP3:%.*]] = icmp eq i8 49, [[TMP0]]
41+
; CHECK-NEXT: [[TMP4:%.*]] = select i1 [[TMP3]], ptr getelementptr (i8, ptr @str, i64 1), ptr [[TMP2]]
42+
; CHECK-NEXT: [[TMP5:%.*]] = icmp eq i8 0, [[TMP0]]
43+
; CHECK-NEXT: [[TMP6:%.*]] = select i1 [[TMP5]], ptr getelementptr (i8, ptr @str, i64 2), ptr [[TMP4]]
44+
; CHECK-NEXT: [[TMP7:%.*]] = icmp eq i8 50, [[TMP0]]
45+
; CHECK-NEXT: [[TMP8:%.*]] = select i1 [[TMP7]], ptr getelementptr (i8, ptr @str, i64 3), ptr [[TMP6]]
46+
; CHECK-NEXT: [[TMP9:%.*]] = icmp eq i8 0, [[TMP0]]
47+
; CHECK-NEXT: [[MEMCHR4:%.*]] = select i1 [[TMP9]], ptr getelementptr (i8, ptr @str, i64 4), ptr [[TMP8]]
6848
; CHECK-NEXT: ret ptr [[MEMCHR4]]
6949
;
7050
entry:
@@ -75,25 +55,14 @@ entry:
7555
define ptr @test_memchr_smaller_n(i32 %x) {
7656
; CHECK-LABEL: define ptr @test_memchr_smaller_n(
7757
; CHECK-SAME: i32 [[X:%.*]]) {
78-
; CHECK-NEXT: [[ENTRY:.*]]:
58+
; CHECK-NEXT: [[ENTRY:.*:]]
7959
; CHECK-NEXT: [[TMP0:%.*]] = trunc i32 [[X]] to i8
80-
; CHECK-NEXT: switch i8 [[TMP0]], label %[[ENTRY_SPLIT:.*]] [
81-
; CHECK-NEXT: i8 48, label %[[MEMCHR_CASE:.*]]
82-
; CHECK-NEXT: i8 49, label %[[MEMCHR_CASE1:.*]]
83-
; CHECK-NEXT: i8 0, label %[[MEMCHR_CASE2:.*]]
84-
; CHECK-NEXT: ]
85-
; CHECK: [[MEMCHR_CASE]]:
86-
; CHECK-NEXT: br label %[[MEMCHR_SUCCESS:.*]]
87-
; CHECK: [[MEMCHR_CASE1]]:
88-
; CHECK-NEXT: br label %[[MEMCHR_SUCCESS]]
89-
; CHECK: [[MEMCHR_CASE2]]:
90-
; CHECK-NEXT: br label %[[MEMCHR_SUCCESS]]
91-
; CHECK: [[MEMCHR_SUCCESS]]:
92-
; CHECK-NEXT: [[MEMCHR_IDX:%.*]] = phi i64 [ 0, %[[MEMCHR_CASE]] ], [ 1, %[[MEMCHR_CASE1]] ], [ 2, %[[MEMCHR_CASE2]] ]
93-
; CHECK-NEXT: [[TMP1:%.*]] = getelementptr inbounds i8, ptr @str, i64 [[MEMCHR_IDX]]
94-
; CHECK-NEXT: br label %[[ENTRY_SPLIT]]
95-
; CHECK: [[ENTRY_SPLIT]]:
96-
; CHECK-NEXT: [[MEMCHR3:%.*]] = phi ptr [ null, %[[ENTRY]] ], [ [[TMP1]], %[[MEMCHR_SUCCESS]] ]
60+
; CHECK-NEXT: [[TMP1:%.*]] = icmp eq i8 48, [[TMP0]]
61+
; CHECK-NEXT: [[TMP2:%.*]] = select i1 [[TMP1]], ptr @str, ptr null
62+
; CHECK-NEXT: [[TMP3:%.*]] = icmp eq i8 49, [[TMP0]]
63+
; CHECK-NEXT: [[TMP4:%.*]] = select i1 [[TMP3]], ptr getelementptr (i8, ptr @str, i64 1), ptr [[TMP2]]
64+
; CHECK-NEXT: [[TMP5:%.*]] = icmp eq i8 0, [[TMP0]]
65+
; CHECK-NEXT: [[MEMCHR3:%.*]] = select i1 [[TMP5]], ptr getelementptr (i8, ptr @str, i64 2), ptr [[TMP4]]
9766
; CHECK-NEXT: ret ptr [[MEMCHR3]]
9867
;
9968
entry:
@@ -119,7 +88,26 @@ define ptr @test_memchr_non_constant(i32 %x, ptr %str) {
11988
; CHECK-LABEL: define ptr @test_memchr_non_constant(
12089
; CHECK-SAME: i32 [[X:%.*]], ptr [[STR:%.*]]) {
12190
; CHECK-NEXT: [[ENTRY:.*:]]
122-
; CHECK-NEXT: [[MEMCHR:%.*]] = call ptr @memchr(ptr [[STR]], i32 [[X]], i64 5)
91+
; CHECK-NEXT: [[TMP0:%.*]] = trunc i32 [[X]] to i8
92+
; CHECK-NEXT: [[TMP1:%.*]] = load i8, ptr [[STR]], align 1
93+
; CHECK-NEXT: [[TMP2:%.*]] = icmp eq i8 [[TMP1]], [[TMP0]]
94+
; CHECK-NEXT: [[TMP3:%.*]] = select i1 [[TMP2]], ptr [[STR]], ptr null
95+
; CHECK-NEXT: [[TMP4:%.*]] = getelementptr i8, ptr [[STR]], i64 1
96+
; CHECK-NEXT: [[TMP5:%.*]] = load i8, ptr [[TMP4]], align 1
97+
; CHECK-NEXT: [[TMP6:%.*]] = icmp eq i8 [[TMP5]], [[TMP0]]
98+
; CHECK-NEXT: [[TMP7:%.*]] = select i1 [[TMP6]], ptr [[TMP4]], ptr [[TMP3]]
99+
; CHECK-NEXT: [[TMP8:%.*]] = getelementptr i8, ptr [[STR]], i64 2
100+
; CHECK-NEXT: [[TMP9:%.*]] = load i8, ptr [[TMP8]], align 1
101+
; CHECK-NEXT: [[TMP10:%.*]] = icmp eq i8 [[TMP9]], [[TMP0]]
102+
; CHECK-NEXT: [[TMP11:%.*]] = select i1 [[TMP10]], ptr [[TMP8]], ptr [[TMP7]]
103+
; CHECK-NEXT: [[TMP12:%.*]] = getelementptr i8, ptr [[STR]], i64 3
104+
; CHECK-NEXT: [[TMP13:%.*]] = load i8, ptr [[TMP12]], align 1
105+
; CHECK-NEXT: [[TMP14:%.*]] = icmp eq i8 [[TMP13]], [[TMP0]]
106+
; CHECK-NEXT: [[TMP15:%.*]] = select i1 [[TMP14]], ptr [[TMP12]], ptr [[TMP11]]
107+
; CHECK-NEXT: [[TMP16:%.*]] = getelementptr i8, ptr [[STR]], i64 4
108+
; CHECK-NEXT: [[TMP17:%.*]] = load i8, ptr [[TMP16]], align 1
109+
; CHECK-NEXT: [[TMP18:%.*]] = icmp eq i8 [[TMP17]], [[TMP0]]
110+
; CHECK-NEXT: [[MEMCHR:%.*]] = select i1 [[TMP18]], ptr [[TMP16]], ptr [[TMP15]]
123111
; CHECK-NEXT: ret ptr [[MEMCHR]]
124112
;
125113
entry:
@@ -130,8 +118,7 @@ entry:
130118
define ptr @test_memchr_constant_ch() {
131119
; CHECK-LABEL: define ptr @test_memchr_constant_ch() {
132120
; CHECK-NEXT: [[ENTRY:.*:]]
133-
; CHECK-NEXT: [[MEMCHR:%.*]] = call ptr @memchr(ptr @str, i32 49, i64 5)
134-
; CHECK-NEXT: ret ptr [[MEMCHR]]
121+
; CHECK-NEXT: ret ptr getelementptr (i8, ptr @str, i64 1)
135122
;
136123
entry:
137124
%memchr = call ptr @memchr(ptr @str, i32 49, i64 5)

‎llvm/test/Transforms/AggressiveInstCombine/test_memchr_small.ll‎

Lines changed: 23 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -0,0 +1,23 @@
1+
; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 5
2+
; RUN: opt -S -passes=aggressive-instcombine --memchr-inline-threshold=2 < %s | FileCheck %s
3+
4+
declare ptr @memchr(ptr, i32, i64)
5+
6+
define ptr @test_memchr_small(ptr %p, i32 %val) {
7+
; CHECK-LABEL: define ptr @test_memchr_small(
8+
; CHECK-SAME: ptr [[P:%.*]], i32 [[VAL:%.*]]) {
9+
; CHECK-NEXT: [[ENTRY:.*:]]
10+
; CHECK-NEXT: [[TMP0:%.*]] = trunc i32 [[VAL]] to i8
11+
; CHECK-NEXT: [[TMP1:%.*]] = load i8, ptr [[P]], align 1
12+
; CHECK-NEXT: [[TMP2:%.*]] = icmp eq i8 [[TMP1]], [[TMP0]]
13+
; CHECK-NEXT: [[TMP3:%.*]] = select i1 [[TMP2]], ptr [[P]], ptr null
14+
; CHECK-NEXT: [[TMP4:%.*]] = getelementptr i8, ptr [[P]], i64 1
15+
; CHECK-NEXT: [[TMP5:%.*]] = load i8, ptr [[TMP4]], align 1
16+
; CHECK-NEXT: [[TMP6:%.*]] = icmp eq i8 [[TMP5]], [[TMP0]]
17+
; CHECK-NEXT: [[TMP7:%.*]] = select i1 [[TMP6]], ptr [[TMP4]], ptr [[TMP3]]
18+
; CHECK-NEXT: ret ptr [[TMP7]]
19+
;
20+
entry:
21+
%res = call ptr @memchr(ptr %p, i32 %val, i64 2)
22+
ret ptr %res
23+
}

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