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[SimplifyCFG] handle monotonic wrapped case for D150943 #65882

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Merged
merged 1 commit into from
Sep 14, 2023
Merged

[SimplifyCFG] handle monotonic wrapped case for D150943 #65882

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12 changes: 8 additions & 4 deletions llvm/lib/Transforms/Utils/SimplifyCFG.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -6061,8 +6061,9 @@ SwitchLookupTable::SwitchLookupTable(
bool LinearMappingPossible = true;
APInt PrevVal;
APInt DistToPrev;
// When linear map is monotonic, we can attach nsw.
bool Wrapped = false;
// When linear map is monotonic and signed overflow doesn't happen on
// maximum index, we can attach nsw on Add and Mul.
bool NonMonotonic = false;
assert(TableSize >= 2 && "Should be a SingleValue table.");
// Check if there is the same distance between two consecutive values.
for (uint64_t I = 0; I < TableSize; ++I) {
Expand All @@ -6082,15 +6083,18 @@ SwitchLookupTable::SwitchLookupTable(
LinearMappingPossible = false;
break;
}
Wrapped |=
NonMonotonic |=
Dist.isStrictlyPositive() ? Val.sle(PrevVal) : Val.sgt(PrevVal);
}
PrevVal = Val;
}
if (LinearMappingPossible) {
LinearOffset = cast<ConstantInt>(TableContents[0]);
LinearMultiplier = ConstantInt::get(M.getContext(), DistToPrev);
LinearMapValWrapped = Wrapped;
bool MayWrap = false;
APInt M = LinearMultiplier->getValue();
(void)M.smul_ov(APInt(M.getBitWidth(), TableSize - 1), MayWrap);
LinearMapValWrapped = NonMonotonic || MayWrap;
Kind = LinearMapKind;
++NumLinearMaps;
return;
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29 changes: 29 additions & 0 deletions llvm/test/Transforms/SimplifyCFG/X86/switch_to_lookup_table.ll
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Expand Up @@ -2039,3 +2039,32 @@ return:
%x = phi i8 [ 3, %sw.default ], [ 124, %sw.bb3 ], [ -99, %sw.bb2 ], [ -66, %sw.bb1 ], [ -33, %entry ]
ret i8 %x
}

define i8 @linearmap_dec_wrapped_mon(i3 %0) {
; CHECK-LABEL: @linearmap_dec_wrapped_mon(
; CHECK-NEXT: entry:
; CHECK-NEXT: [[SWITCH_TABLEIDX:%.*]] = sub i3 [[TMP0:%.*]], -2
; CHECK-NEXT: [[TMP1:%.*]] = icmp ult i3 [[SWITCH_TABLEIDX]], -4
; CHECK-NEXT: [[SWITCH_IDX_MULT:%.*]] = mul i3 [[SWITCH_TABLEIDX]], 2
; CHECK-NEXT: [[SWITCH_OFFSET:%.*]] = add i3 [[SWITCH_IDX_MULT]], -4
; CHECK-NEXT: [[COND:%.*]] = select i1 [[TMP1]], i3 [[SWITCH_OFFSET]], i3 2
; CHECK-NEXT: [[CONV:%.*]] = sext i3 [[COND]] to i8
; CHECK-NEXT: ret i8 [[CONV]]
;
entry:
switch i3 %0, label %cond.end [
i3 -1, label %cond.false
i3 -2, label %cond.false
i3 1, label %cond.false
i3 0, label %cond.false
]

cond.false: ; preds = %entry, %entry, %entry, %entry
%mul = shl nsw i3 %0, 1
br label %cond.end

cond.end: ; preds = %entry, %cond.false
%cond = phi i3 [ %mul, %cond.false ], [ 2, %entry ]
%conv = sext i3 %cond to i8
ret i8 %conv
}