[llvm] [SimplifyCFG] Find the minimal table considering overflow in `switchToLookupTable` (PR #67885)
Quentin Dian via llvm-commits
llvm-commits at lists.llvm.org
Sat Dec 30 05:35:49 PST 2023
https://github.com/DianQK updated https://github.com/llvm/llvm-project/pull/67885
>From b489f669db81f552197ac1668cdfca83a33a10da Mon Sep 17 00:00:00 2001
From: DianQK <dianqk at dianqk.net>
Date: Thu, 28 Sep 2023 18:06:52 -0600
Subject: [PATCH 1/2] [SimplifyCFG] Pre-commit test for `switchToLookupTable`
---
.../SimplifyCFG/X86/switch_to_lookup_table.ll | 119 ++++++++++++++++++
1 file changed, 119 insertions(+)
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 3873f0c0ae0bbd5..8a6b3165ce03f5d 100644
--- a/llvm/test/Transforms/SimplifyCFG/X86/switch_to_lookup_table.ll
+++ b/llvm/test/Transforms/SimplifyCFG/X86/switch_to_lookup_table.ll
@@ -115,6 +115,125 @@ return:
}
+; The minimal table range is [122, -128]([122, 128]).
+
+define i32 @f_i8_128(i8 %c) {
+; CHECK-LABEL: @f_i8_128(
+; CHECK-NEXT: entry:
+; CHECK-NEXT: switch i8 [[C:%.*]], label [[SW_DEFAULT:%.*]] [
+; CHECK-NEXT: i8 122, label [[RETURN:%.*]]
+; CHECK-NEXT: i8 123, label [[SW_BB1:%.*]]
+; CHECK-NEXT: i8 124, label [[SW_BB2:%.*]]
+; CHECK-NEXT: i8 125, label [[SW_BB3:%.*]]
+; CHECK-NEXT: i8 126, label [[SW_BB4:%.*]]
+; CHECK-NEXT: i8 127, label [[SW_BB5:%.*]]
+; CHECK-NEXT: i8 -128, label [[SW_BB6:%.*]]
+; CHECK-NEXT: ]
+; CHECK: sw.bb1:
+; CHECK-NEXT: br label [[RETURN]]
+; CHECK: sw.bb2:
+; CHECK-NEXT: br label [[RETURN]]
+; CHECK: sw.bb3:
+; CHECK-NEXT: br label [[RETURN]]
+; CHECK: sw.bb4:
+; CHECK-NEXT: br label [[RETURN]]
+; CHECK: sw.bb5:
+; CHECK-NEXT: br label [[RETURN]]
+; CHECK: sw.bb6:
+; CHECK-NEXT: br label [[RETURN]]
+; CHECK: sw.default:
+; CHECK-NEXT: br label [[RETURN]]
+; CHECK: return:
+; CHECK-NEXT: [[RETVAL_0:%.*]] = phi i32 [ 15, [[SW_DEFAULT]] ], [ 1, [[SW_BB6]] ], [ 62, [[SW_BB5]] ], [ 27, [[SW_BB4]] ], [ -1, [[SW_BB3]] ], [ 0, [[SW_BB2]] ], [ 123, [[SW_BB1]] ], [ 55, [[ENTRY:%.*]] ]
+; CHECK-NEXT: ret i32 [[RETVAL_0]]
+;
+entry:
+ switch i8 %c, label %sw.default [
+ i8 122, label %return
+ i8 123, label %sw.bb1
+ i8 124, label %sw.bb2
+ i8 125, label %sw.bb3
+ i8 126, label %sw.bb4
+ i8 127, label %sw.bb5
+ i8 -128, label %sw.bb6
+ ]
+
+sw.bb1: br label %return
+sw.bb2: br label %return
+sw.bb3: br label %return
+sw.bb4: br label %return
+sw.bb5: br label %return
+sw.bb6: br label %return
+sw.default: br label %return
+return:
+ %retval.0 = phi i32 [ 15, %sw.default ], [ 1, %sw.bb6 ], [ 62, %sw.bb5 ], [ 27, %sw.bb4 ], [ -1, %sw.bb3 ], [ 0, %sw.bb2 ], [ 123, %sw.bb1 ], [ 55, %entry ]
+ ret i32 %retval.0
+}
+
+; The minimal table range is [3, 0].
+
+define i32 @f_min_max(i3 %c) {
+; CHECK-LABEL: @f_min_max(
+; CHECK-NEXT: entry:
+; CHECK-NEXT: [[SWITCH_TABLEIDX:%.*]] = sub i3 [[C:%.*]], -4
+; CHECK-NEXT: [[SWITCH_TABLEIDX_ZEXT:%.*]] = zext i3 [[SWITCH_TABLEIDX]] to i4
+; CHECK-NEXT: [[SWITCH_GEP:%.*]] = getelementptr inbounds [8 x i32], ptr @switch.table.f_min_max, i32 0, i4 [[SWITCH_TABLEIDX_ZEXT]]
+; CHECK-NEXT: [[SWITCH_LOAD:%.*]] = load i32, ptr [[SWITCH_GEP]], align 4
+; CHECK-NEXT: ret i32 [[SWITCH_LOAD]]
+;
+entry:
+ switch i3 %c, label %sw.default [
+ i3 -4, label %return
+ i3 -3, label %sw.bb1
+ i3 -2, label %sw.bb2
+ i3 -1, label %sw.bb3
+ i3 0, label %sw.bb4
+ i3 3, label %sw.bb6
+ ]
+
+sw.bb1: br label %return
+sw.bb2: br label %return
+sw.bb3: br label %return
+sw.bb4: br label %return
+sw.bb6: br label %return
+sw.default: br label %return
+return:
+ %retval.0 = phi i32 [ 15, %sw.default ], [ 1, %sw.bb6 ], [ 27, %sw.bb4 ], [ -1, %sw.bb3 ], [ 0, %sw.bb2 ], [ 123, %sw.bb1 ], [ 55, %entry ]
+ ret i32 %retval.0
+}
+
+; The minimal table range is [-1, -4].
+
+define i32 @f_min_max_2(i3 %c) {
+; CHECK-LABEL: @f_min_max_2(
+; CHECK-NEXT: entry:
+; CHECK-NEXT: [[SWITCH_TABLEIDX:%.*]] = sub i3 [[C:%.*]], -4
+; CHECK-NEXT: [[SWITCH_TABLEIDX_ZEXT:%.*]] = zext i3 [[SWITCH_TABLEIDX]] to i4
+; CHECK-NEXT: [[SWITCH_GEP:%.*]] = getelementptr inbounds [8 x i32], ptr @switch.table.f_min_max_2, i32 0, i4 [[SWITCH_TABLEIDX_ZEXT]]
+; CHECK-NEXT: [[SWITCH_LOAD:%.*]] = load i32, ptr [[SWITCH_GEP]], align 4
+; CHECK-NEXT: ret i32 [[SWITCH_LOAD]]
+;
+entry:
+ switch i3 %c, label %sw.default [
+ i3 -1, label %return
+ i3 0, label %sw.bb1
+ i3 1, label %sw.bb2
+ i3 2, label %sw.bb3
+ i3 3, label %sw.bb4
+ i3 -4, label %sw.bb6
+ ]
+
+sw.bb1: br label %return
+sw.bb2: br label %return
+sw.bb3: br label %return
+sw.bb4: br label %return
+sw.bb6: br label %return
+sw.default: br label %return
+return:
+ %retval.0 = phi i32 [ 15, %sw.default ], [ 1, %sw.bb6 ], [ 27, %sw.bb4 ], [ -1, %sw.bb3 ], [ 0, %sw.bb2 ], [ 123, %sw.bb1 ], [ 55, %entry ]
+ ret i32 %retval.0
+}
+
; A switch used to initialize two variables, an i8 and a float.
declare void @dummy(i8 signext, float)
>From 83c73041d5dbfffea3c5a84fe4d6ab73211b84e9 Mon Sep 17 00:00:00 2001
From: DianQK <dianqk at dianqk.net>
Date: Thu, 28 Sep 2023 18:07:06 -0600
Subject: [PATCH 2/2] [SimplifyCFG] Find the smallest table considering
overflow in `switchToLookupTable`
---
llvm/lib/Transforms/Utils/SimplifyCFG.cpp | 92 +++++++++++++------
.../SimplifyCFG/X86/switch_to_lookup_table.ll | 30 ++----
2 files changed, 71 insertions(+), 51 deletions(-)
diff --git a/llvm/lib/Transforms/Utils/SimplifyCFG.cpp b/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
index 55e375670cc61e4..24c9f640f86c4c6 100644
--- a/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
+++ b/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
@@ -6435,18 +6435,20 @@ ShouldBuildLookupTable(SwitchInst *SI, uint64_t TableSize,
}
static bool ShouldUseSwitchConditionAsTableIndex(
- ConstantInt &MinCaseVal, const ConstantInt &MaxCaseVal,
+ const ConstantInt &BeginCaseVal, const ConstantInt &EndCaseVal,
bool HasDefaultResults, const SmallDenseMap<PHINode *, Type *> &ResultTypes,
const DataLayout &DL, const TargetTransformInfo &TTI) {
- if (MinCaseVal.isNullValue())
+ if (BeginCaseVal.isNullValue())
return true;
- if (MinCaseVal.isNegative() ||
- MaxCaseVal.getLimitedValue() == std::numeric_limits<uint64_t>::max() ||
+ if (BeginCaseVal.getValue().sge(EndCaseVal.getValue()))
+ return false;
+ if (BeginCaseVal.isNegative() ||
+ EndCaseVal.getLimitedValue() == std::numeric_limits<uint64_t>::max() ||
!HasDefaultResults)
return false;
return all_of(ResultTypes, [&](const auto &KV) {
return SwitchLookupTable::WouldFitInRegister(
- DL, MaxCaseVal.getLimitedValue() + 1 /* TableSize */,
+ DL, EndCaseVal.getLimitedValue() + 1 /* TableSize */,
KV.second /* ResultType */);
});
}
@@ -6537,7 +6539,8 @@ static void reuseTableCompare(
/// lookup tables.
static bool SwitchToLookupTable(SwitchInst *SI, IRBuilder<> &Builder,
DomTreeUpdater *DTU, const DataLayout &DL,
- const TargetTransformInfo &TTI) {
+ const TargetTransformInfo &TTI,
+ bool TryMinTableSize) {
assert(SI->getNumCases() > 1 && "Degenerate switch?");
BasicBlock *BB = SI->getParent();
@@ -6563,9 +6566,6 @@ static bool SwitchToLookupTable(SwitchInst *SI, IRBuilder<> &Builder,
// Figure out the corresponding result for each case value and phi node in the
// common destination, as well as the min and max case values.
assert(!SI->cases().empty());
- SwitchInst::CaseIt CI = SI->case_begin();
- ConstantInt *MinCaseVal = CI->getCaseValue();
- ConstantInt *MaxCaseVal = CI->getCaseValue();
BasicBlock *CommonDest = nullptr;
@@ -6576,17 +6576,49 @@ static bool SwitchToLookupTable(SwitchInst *SI, IRBuilder<> &Builder,
SmallDenseMap<PHINode *, Type *> ResultTypes;
SmallVector<PHINode *, 4> PHIs;
- for (SwitchInst::CaseIt E = SI->case_end(); CI != E; ++CI) {
- ConstantInt *CaseVal = CI->getCaseValue();
- if (CaseVal->getValue().slt(MinCaseVal->getValue()))
- MinCaseVal = CaseVal;
- if (CaseVal->getValue().sgt(MaxCaseVal->getValue()))
- MaxCaseVal = CaseVal;
+ SmallVector<ConstantInt *, 8> CaseVals(llvm::map_range(
+ SI->cases(), [](const auto &C) { return C.getCaseValue(); }));
+
+ llvm::sort(CaseVals, [](const auto *L, const auto *R) {
+ return L->getValue().slt(R->getValue());
+ });
+ auto *CaseValIter = CaseVals.begin();
+ ConstantInt *BeginCaseVal = *CaseValIter;
+ ConstantInt *EndCaseVal = CaseVals.back();
+ bool RangeOverflow = false;
+ uint64_t MinTableSize = EndCaseVal->getValue()
+ .ssub_ov(BeginCaseVal->getValue(), RangeOverflow)
+ .getLimitedValue() +
+ 1;
+ // If there is no overflow, then this must be the minimal table.
+ // The signed max-min can no longer build a lookup table, so return.
+ if (RangeOverflow && TryMinTableSize) {
+ // We consider cases where the starting to the endpoint will cross the
+ // signed max and min. For example, for the i8 range `[-128, -127, 126,
+ // 127]`, we choose from 126 to -127. The length of the lookup table is 4.
+ while (CaseValIter != CaseVals.end()) {
+ auto *CurCaseVal = *CaseValIter++;
+ if (CaseValIter == CaseVals.end())
+ break;
+ auto *NextCaseVal = *CaseValIter;
+ const auto &NextVal = NextCaseVal->getValue();
+ const auto &CurVal = CurCaseVal->getValue();
+ uint64_t RequireTableSize = (CurVal - NextVal).getLimitedValue() + 1;
+ if (RequireTableSize < MinTableSize) {
+ BeginCaseVal = NextCaseVal;
+ EndCaseVal = CurCaseVal;
+ MinTableSize = RequireTableSize;
+ }
+ }
+ }
+
+ for (const auto &CI : SI->cases()) {
+ ConstantInt *CaseVal = CI.getCaseValue();
// Resulting value at phi nodes for this case value.
using ResultsTy = SmallVector<std::pair<PHINode *, Constant *>, 4>;
ResultsTy Results;
- if (!getCaseResults(SI, CaseVal, CI->getCaseSuccessor(), &CommonDest,
+ if (!getCaseResults(SI, CaseVal, CI.getCaseSuccessor(), &CommonDest,
Results, DL, TTI))
return false;
@@ -6621,13 +6653,12 @@ static bool SwitchToLookupTable(SwitchInst *SI, IRBuilder<> &Builder,
}
bool UseSwitchConditionAsTableIndex = ShouldUseSwitchConditionAsTableIndex(
- *MinCaseVal, *MaxCaseVal, HasDefaultResults, ResultTypes, DL, TTI);
+ *BeginCaseVal, *EndCaseVal, HasDefaultResults, ResultTypes, DL, TTI);
uint64_t TableSize;
if (UseSwitchConditionAsTableIndex)
- TableSize = MaxCaseVal->getLimitedValue() + 1;
+ TableSize = EndCaseVal->getLimitedValue() + 1;
else
- TableSize =
- (MaxCaseVal->getValue() - MinCaseVal->getValue()).getLimitedValue() + 1;
+ TableSize = MinTableSize;
bool TableHasHoles = (NumResults < TableSize);
bool NeedMask = (TableHasHoles && !HasDefaultResults);
@@ -6640,13 +6671,16 @@ static bool SwitchToLookupTable(SwitchInst *SI, IRBuilder<> &Builder,
}
if (!ShouldBuildLookupTable(SI, TableSize, TTI, DL, ResultTypes))
- return false;
+ // When a signed max-min cannot construct a lookup table, try to find a
+ // range with a minimal lookup table.
+ return !TryMinTableSize &&
+ SwitchToLookupTable(SI, Builder, DTU, DL, TTI, true);
std::vector<DominatorTree::UpdateType> Updates;
// Compute the maximum table size representable by the integer type we are
// switching upon.
- unsigned CaseSize = MinCaseVal->getType()->getPrimitiveSizeInBits();
+ unsigned CaseSize = BeginCaseVal->getType()->getPrimitiveSizeInBits();
uint64_t MaxTableSize = CaseSize > 63 ? UINT64_MAX : 1ULL << CaseSize;
assert(MaxTableSize >= TableSize &&
"It is impossible for a switch to have more entries than the max "
@@ -6668,15 +6702,17 @@ static bool SwitchToLookupTable(SwitchInst *SI, IRBuilder<> &Builder,
Value *TableIndex;
ConstantInt *TableIndexOffset;
if (UseSwitchConditionAsTableIndex) {
- TableIndexOffset = ConstantInt::get(MaxCaseVal->getIntegerType(), 0);
+ TableIndexOffset = ConstantInt::get(EndCaseVal->getIntegerType(), 0);
TableIndex = SI->getCondition();
} else {
- TableIndexOffset = MinCaseVal;
+ TableIndexOffset = BeginCaseVal;
// If the default is unreachable, all case values are s>= MinCaseVal. Then
// we can try to attach nsw.
bool MayWrap = true;
- if (!DefaultIsReachable) {
- APInt Res = MaxCaseVal->getValue().ssub_ov(MinCaseVal->getValue(), MayWrap);
+ if (!DefaultIsReachable &&
+ EndCaseVal->getValue().sge(BeginCaseVal->getValue())) {
+ APInt Res =
+ EndCaseVal->getValue().ssub_ov(BeginCaseVal->getValue(), MayWrap);
(void)Res;
}
@@ -6717,7 +6753,7 @@ static bool SwitchToLookupTable(SwitchInst *SI, IRBuilder<> &Builder,
// PHI value for the default case in case we're using a bit mask.
} else {
Value *Cmp = Builder.CreateICmpULT(
- TableIndex, ConstantInt::get(MinCaseVal->getType(), TableSize));
+ TableIndex, ConstantInt::get(BeginCaseVal->getType(), TableSize));
RangeCheckBranch =
Builder.CreateCondBr(Cmp, LookupBB, SI->getDefaultDest());
if (DTU)
@@ -7032,7 +7068,7 @@ bool SimplifyCFGOpt::simplifySwitch(SwitchInst *SI, IRBuilder<> &Builder) {
// CVP. Therefore, only apply this transformation during late stages of the
// optimisation pipeline.
if (Options.ConvertSwitchToLookupTable &&
- SwitchToLookupTable(SI, Builder, DTU, DL, TTI))
+ SwitchToLookupTable(SI, Builder, DTU, DL, TTI, false))
return requestResimplify();
if (simplifySwitchOfPowersOfTwo(SI, Builder, DL, TTI))
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 8a6b3165ce03f5d..dde39aea3c1fd57 100644
--- a/llvm/test/Transforms/SimplifyCFG/X86/switch_to_lookup_table.ll
+++ b/llvm/test/Transforms/SimplifyCFG/X86/switch_to_lookup_table.ll
@@ -120,31 +120,15 @@ return:
define i32 @f_i8_128(i8 %c) {
; CHECK-LABEL: @f_i8_128(
; CHECK-NEXT: entry:
-; CHECK-NEXT: switch i8 [[C:%.*]], label [[SW_DEFAULT:%.*]] [
-; CHECK-NEXT: i8 122, label [[RETURN:%.*]]
-; CHECK-NEXT: i8 123, label [[SW_BB1:%.*]]
-; CHECK-NEXT: i8 124, label [[SW_BB2:%.*]]
-; CHECK-NEXT: i8 125, label [[SW_BB3:%.*]]
-; CHECK-NEXT: i8 126, label [[SW_BB4:%.*]]
-; CHECK-NEXT: i8 127, label [[SW_BB5:%.*]]
-; CHECK-NEXT: i8 -128, label [[SW_BB6:%.*]]
-; CHECK-NEXT: ]
-; CHECK: sw.bb1:
-; CHECK-NEXT: br label [[RETURN]]
-; CHECK: sw.bb2:
-; CHECK-NEXT: br label [[RETURN]]
-; CHECK: sw.bb3:
-; CHECK-NEXT: br label [[RETURN]]
-; CHECK: sw.bb4:
-; CHECK-NEXT: br label [[RETURN]]
-; CHECK: sw.bb5:
-; CHECK-NEXT: br label [[RETURN]]
-; CHECK: sw.bb6:
-; CHECK-NEXT: br label [[RETURN]]
-; CHECK: sw.default:
+; CHECK-NEXT: [[SWITCH_TABLEIDX:%.*]] = sub i8 [[C:%.*]], 122
+; CHECK-NEXT: [[TMP0:%.*]] = icmp ult i8 [[SWITCH_TABLEIDX]], 7
+; CHECK-NEXT: br i1 [[TMP0]], label [[SWITCH_LOOKUP:%.*]], label [[RETURN:%.*]]
+; CHECK: switch.lookup:
+; CHECK-NEXT: [[SWITCH_GEP:%.*]] = getelementptr inbounds [7 x i32], ptr @switch.table.f_i8_128, i32 0, i8 [[SWITCH_TABLEIDX]]
+; CHECK-NEXT: [[SWITCH_LOAD:%.*]] = load i32, ptr [[SWITCH_GEP]], align 4
; CHECK-NEXT: br label [[RETURN]]
; CHECK: return:
-; CHECK-NEXT: [[RETVAL_0:%.*]] = phi i32 [ 15, [[SW_DEFAULT]] ], [ 1, [[SW_BB6]] ], [ 62, [[SW_BB5]] ], [ 27, [[SW_BB4]] ], [ -1, [[SW_BB3]] ], [ 0, [[SW_BB2]] ], [ 123, [[SW_BB1]] ], [ 55, [[ENTRY:%.*]] ]
+; CHECK-NEXT: [[RETVAL_0:%.*]] = phi i32 [ [[SWITCH_LOAD]], [[SWITCH_LOOKUP]] ], [ 15, [[ENTRY:%.*]] ]
; CHECK-NEXT: ret i32 [[RETVAL_0]]
;
entry:
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