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[SimplifyCFG] Fix the compile crash for invalid upper bound value (ll…
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…vm#71351)

Fix the crash for the last land PR70542.

Note:
For '%add = add nuw i32 %x, 1', we can only infer the LowerBound is 1,
but the UpperBound is wrapped to 0 in computeConstantRange.
so we can't assume the UpperBound is valid bound when its value is 0.

Fix llvm#71329.
Reviewed By: zmodem, nikic
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@vfdff
vfdff authored Nov 9, 2023
1 parent 919f5ef commit 7ec86f4
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Showing 2 changed files with 144 additions and 16 deletions.
25 changes: 23 additions & 2 deletions llvm/lib/Transforms/Utils/SimplifyCFG.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -6598,9 +6598,8 @@ static bool SwitchToLookupTable(SwitchInst *SI, IRBuilder<> &Builder,
// If the default destination is unreachable, or if the lookup table covers
// all values of the conditional variable, branch directly to the lookup table
// BB. Otherwise, check that the condition is within the case range.
const bool DefaultIsReachable =
bool DefaultIsReachable =
!isa<UnreachableInst>(SI->getDefaultDest()->getFirstNonPHIOrDbg());
const bool GeneratingCoveredLookupTable = (MaxTableSize == TableSize);

// Create the BB that does the lookups.
Module &Mod = *CommonDest->getParent()->getParent();
Expand Down Expand Up @@ -6631,6 +6630,28 @@ static bool SwitchToLookupTable(SwitchInst *SI, IRBuilder<> &Builder,

BranchInst *RangeCheckBranch = nullptr;

// Grow the table to cover all possible index values to avoid the range check.
// It will use the default result to fill in the table hole later, so make
// sure it exist.
if (UseSwitchConditionAsTableIndex && HasDefaultResults) {
ConstantRange CR = computeConstantRange(TableIndex, /* ForSigned */ false);
// Grow the table shouldn't have any size impact by checking
// WouldFitInRegister.
// TODO: Consider growing the table also when it doesn't fit in a register
// if no optsize is specified.
const uint64_t UpperBound = CR.getUpper().getLimitedValue();
if (!CR.isUpperWrapped() && all_of(ResultTypes, [&](const auto &KV) {
return SwitchLookupTable::WouldFitInRegister(
DL, UpperBound, KV.second /* ResultType */);
})) {
// The default branch is unreachable after we enlarge the lookup table.
// Adjust DefaultIsReachable to reuse code path.
TableSize = UpperBound;
DefaultIsReachable = false;
}
}

const bool GeneratingCoveredLookupTable = (MaxTableSize == TableSize);
if (!DefaultIsReachable || GeneratingCoveredLookupTable) {
Builder.CreateBr(LookupBB);
if (DTU)
Expand Down
135 changes: 121 additions & 14 deletions llvm/test/Transforms/SimplifyCFG/switch_mask.ll
View file
Original file line number Diff line number Diff line change
Expand Up @@ -3,18 +3,18 @@

target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"

declare i1 @foo()

; https://alive2.llvm.org/ce/z/tuxLhJ
define i1 @switch_lookup_with_small_i1(i64 %x) {
; CHECK-LABEL: @switch_lookup_with_small_i1(
; CHECK-NEXT: entry:
; CHECK-NEXT: [[AND:%.*]] = and i64 [[X:%.*]], 15
; CHECK-NEXT: [[TMP0:%.*]] = icmp ult i64 [[AND]], 11
; CHECK-NEXT: [[SWITCH_CAST:%.*]] = trunc i64 [[AND]] to i11
; CHECK-NEXT: [[SWITCH_SHIFTAMT:%.*]] = mul nuw nsw i11 [[SWITCH_CAST]], 1
; CHECK-NEXT: [[SWITCH_DOWNSHIFT:%.*]] = lshr i11 -1018, [[SWITCH_SHIFTAMT]]
; CHECK-NEXT: [[SWITCH_MASKED:%.*]] = trunc i11 [[SWITCH_DOWNSHIFT]] to i1
; CHECK-NEXT: [[TMP1:%.*]] = select i1 [[TMP0]], i1 [[SWITCH_MASKED]], i1 false
; CHECK-NEXT: ret i1 [[TMP1]]
; CHECK-NEXT: [[SWITCH_CAST:%.*]] = trunc i64 [[AND]] to i16
; CHECK-NEXT: [[SWITCH_SHIFTAMT:%.*]] = mul nuw nsw i16 [[SWITCH_CAST]], 1
; CHECK-NEXT: [[SWITCH_DOWNSHIFT:%.*]] = lshr i16 1030, [[SWITCH_SHIFTAMT]]
; CHECK-NEXT: [[SWITCH_MASKED:%.*]] = trunc i16 [[SWITCH_DOWNSHIFT]] to i1
; CHECK-NEXT: ret i1 [[SWITCH_MASKED]]
;
entry:
%and = and i64 %x, 15
Expand All @@ -37,13 +37,11 @@ define i8 @switch_lookup_with_small_i8(i64 %x) {
; CHECK-LABEL: @switch_lookup_with_small_i8(
; CHECK-NEXT: entry:
; CHECK-NEXT: [[REM:%.*]] = urem i64 [[X:%.*]], 5
; CHECK-NEXT: [[TMP0:%.*]] = icmp ult i64 [[REM]], 3
; CHECK-NEXT: [[SWITCH_CAST:%.*]] = trunc i64 [[REM]] to i24
; CHECK-NEXT: [[SWITCH_SHIFTAMT:%.*]] = mul nuw nsw i24 [[SWITCH_CAST]], 8
; CHECK-NEXT: [[SWITCH_DOWNSHIFT:%.*]] = lshr i24 460303, [[SWITCH_SHIFTAMT]]
; CHECK-NEXT: [[SWITCH_MASKED:%.*]] = trunc i24 [[SWITCH_DOWNSHIFT]] to i8
; CHECK-NEXT: [[TMP1:%.*]] = select i1 [[TMP0]], i8 [[SWITCH_MASKED]], i8 0
; CHECK-NEXT: ret i8 [[TMP1]]
; CHECK-NEXT: [[SWITCH_CAST:%.*]] = trunc i64 [[REM]] to i40
; CHECK-NEXT: [[SWITCH_SHIFTAMT:%.*]] = mul nuw nsw i40 [[SWITCH_CAST]], 8
; CHECK-NEXT: [[SWITCH_DOWNSHIFT:%.*]] = lshr i40 460303, [[SWITCH_SHIFTAMT]]
; CHECK-NEXT: [[SWITCH_MASKED:%.*]] = trunc i40 [[SWITCH_DOWNSHIFT]] to i8
; CHECK-NEXT: ret i8 [[SWITCH_MASKED]]
;
entry:
%rem = urem i64 %x, 5
Expand Down Expand Up @@ -107,3 +105,112 @@ lor.end:
%0 = phi i8 [ 15, %sw.bb0 ], [ 6, %sw.bb1 ], [ 7, %sw.bb2 ], [ 0, %default ]
ret i8 %0
}

; Negative test: The default branch is unreachable, also it has no result.
define i1 @switch_lookup_with_small_i1_default_unreachable(i32 %x) {
; CHECK-LABEL: @switch_lookup_with_small_i1_default_unreachable(
; CHECK-NEXT: entry:
; CHECK-NEXT: [[AND:%.*]] = and i32 [[X:%.*]], 15
; CHECK-NEXT: ret i1 false
;
entry:
%and = and i32 %x, 15
switch i32 %and, label %default [
i32 4, label %phi.end
i32 2, label %phi.end
i32 10, label %phi.end
i32 9, label %phi.end
i32 1, label %sw.bb1.i
i32 3, label %sw.bb1.i
i32 5, label %sw.bb1.i
i32 0, label %sw.bb1.i
i32 6, label %sw.bb1.i
i32 7, label %sw.bb1.i
i32 8, label %sw.bb1.i
]

sw.bb1.i: ; preds = %entry, %entry, %entry, %entry, %entry, %entry, %entry
br label %phi.end

default: ; preds = %entry
unreachable

phi.end: ; preds = %sw.bb1.i, %entry, %entry, %entry, %entry
%retval = phi i1 [ false, %sw.bb1.i ], [ false, %entry ], [ false, %entry ], [ false, %entry ], [ false, %entry ]
ret i1 %retval
}

; Negative test: The result in default reachable, but its value is not const.
define i1 @switch_lookup_with_small_i1_default_nonconst(i64 %x) {
; CHECK-LABEL: @switch_lookup_with_small_i1_default_nonconst(
; CHECK-NEXT: entry:
; CHECK-NEXT: [[AND:%.*]] = and i64 [[X:%.*]], 15
; CHECK-NEXT: switch i64 [[AND]], label [[DEFAULT:%.*]] [
; CHECK-NEXT: i64 10, label [[LOR_END:%.*]]
; CHECK-NEXT: i64 1, label [[LOR_END]]
; CHECK-NEXT: i64 2, label [[LOR_END]]
; CHECK-NEXT: ]
; CHECK: default:
; CHECK-NEXT: [[CALL:%.*]] = tail call i1 @foo()
; CHECK-NEXT: br label [[LOR_END]]
; CHECK: lor.end:
; CHECK-NEXT: [[TMP0:%.*]] = phi i1 [ true, [[ENTRY:%.*]] ], [ [[CALL]], [[DEFAULT]] ], [ true, [[ENTRY]] ], [ true, [[ENTRY]] ]
; CHECK-NEXT: ret i1 [[TMP0]]
;
entry:
%and = and i64 %x, 15
switch i64 %and, label %default [
i64 10, label %lor.end
i64 1, label %lor.end
i64 2, label %lor.end
]

default: ; preds = %entry
%call = tail call i1 @foo()
br label %lor.end

lor.end: ; preds = %entry, %entry, %entry, %default
%0 = phi i1 [ true, %entry ], [ %call, %default ], [ true, %entry ], [ true, %entry ]
ret i1 %0
}

; Negative test: The upper bound index of switch is swapped.
define void @switch_lookup_with_nonconst_range(i32 %x, i1 %cond) {
; CHECK-LABEL: @switch_lookup_with_nonconst_range(
; CHECK-NEXT: entry:
; CHECK-NEXT: br label [[FOR_PREHEADER:%.*]]
; CHECK: for.preheader:
; CHECK-NEXT: [[ADD:%.*]] = add nuw i32 [[X:%.*]], 1
; CHECK-NEXT: br i1 [[COND:%.*]], label [[FOR_PREHEADER]], label [[FOR_END:%.*]]
; CHECK: for.end:
; CHECK-NEXT: [[TMP0:%.*]] = icmp ult i32 [[ADD]], 6
; CHECK-NEXT: br i1 [[TMP0]], label [[SWITCH_LOOKUP:%.*]], label [[LOR_END:%.*]]
; CHECK: switch.lookup:
; CHECK-NEXT: [[SWITCH_GEP:%.*]] = getelementptr inbounds [6 x i32], ptr @switch.table.switch_lookup_with_nonconst_range, i32 0, i32 [[ADD]]
; CHECK-NEXT: [[SWITCH_LOAD:%.*]] = load i32, ptr [[SWITCH_GEP]], align 4
; CHECK-NEXT: br label [[LOR_END]]
; CHECK: lor.end:
; CHECK-NEXT: [[RETVAL_0_I_I:%.*]] = phi i32 [ [[SWITCH_LOAD]], [[SWITCH_LOOKUP]] ], [ 1, [[FOR_END]] ]
; CHECK-NEXT: ret void
;
entry:
br label %for.preheader

for.preheader: ; preds = %for.preheader, %entry
%add = add nuw i32 %x, 1 ; the UpperBound is unconfirmed
br i1 %cond, label %for.preheader, label %for.end

for.end: ; preds = %for.preheader
switch i32 %add, label %default [
i32 0, label %lor.end
i32 1, label %lor.end
i32 5, label %lor.end
]

default: ; preds = %for.end
br label %lor.end

lor.end: ; preds = %default, %for.end, %for.end, %for.end
%retval.0.i.i = phi i32 [ 1, %default ], [ 0, %for.end ], [ 0, %for.end ], [ 0, %for.end ]
ret void
}

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