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[InstCombine] Simplify nested selects with implied condition #83739

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merged 5 commits into from
Mar 5, 2024
Merged

[InstCombine] Simplify nested selects with implied condition #83739

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2abbc12
[InstCombine] Add pre-commit tests. NFC.
dtcxzyw Mar 3, 2024
5bfe453
[InstCombine] Simplify nested selects with implied condition
dtcxzyw Mar 3, 2024
3a3fa92
fixup! [InstCombine] Simplify nested selects with implied condition
dtcxzyw Mar 4, 2024
2e94109
fixup! [InstCombine] Simplify nested selects with implied condition
dtcxzyw Mar 4, 2024
ae3afc5
[InstCombine] Fix assertion failure
dtcxzyw Mar 4, 2024
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84 changes: 33 additions & 51 deletions llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -2643,46 +2643,33 @@ static Value *foldSelectWithFrozenICmp(SelectInst &Sel, InstCombiner::BuilderTy
return nullptr;
}

/// Given that \p CondVal is known to be \p CondIsTrue, try to simplify \p SI.
static Value *simplifyNestedSelectsUsingImpliedCond(SelectInst &SI,
Value *CondVal,
bool CondIsTrue,
const DataLayout &DL) {
Value *InnerCondVal = SI.getCondition();
Value *InnerTrueVal = SI.getTrueValue();
Value *InnerFalseVal = SI.getFalseValue();
assert(CondVal->getType() == InnerCondVal->getType() &&
"The type of inner condition must match with the outer.");
if (auto Implied = isImpliedCondition(CondVal, InnerCondVal, DL, CondIsTrue))
return *Implied ? InnerTrueVal : InnerFalseVal;
return nullptr;
}

Instruction *InstCombinerImpl::foldAndOrOfSelectUsingImpliedCond(Value *Op,
SelectInst &SI,
bool IsAnd) {
Value *CondVal = SI.getCondition();
Value *A = SI.getTrueValue();
Value *B = SI.getFalseValue();

assert(Op->getType()->isIntOrIntVectorTy(1) &&
"Op must be either i1 or vector of i1.");

std::optional<bool> Res = isImpliedCondition(Op, CondVal, DL, IsAnd);
if (!Res)
if (SI.getCondition()->getType() != Op->getType())
return nullptr;

Value *Zero = Constant::getNullValue(A->getType());
Value *One = Constant::getAllOnesValue(A->getType());

if (*Res == true) {
if (IsAnd)
// select op, (select cond, A, B), false => select op, A, false
// and op, (select cond, A, B) => select op, A, false
// if op = true implies condval = true.
return SelectInst::Create(Op, A, Zero);
else
// select op, true, (select cond, A, B) => select op, true, A
// or op, (select cond, A, B) => select op, true, A
// if op = false implies condval = true.
return SelectInst::Create(Op, One, A);
} else {
if (IsAnd)
// select op, (select cond, A, B), false => select op, B, false
// and op, (select cond, A, B) => select op, B, false
// if op = true implies condval = false.
return SelectInst::Create(Op, B, Zero);
else
// select op, true, (select cond, A, B) => select op, true, B
// or op, (select cond, A, B) => select op, true, B
// if op = false implies condval = false.
return SelectInst::Create(Op, One, B);
}
if (Value *V = simplifyNestedSelectsUsingImpliedCond(SI, Op, IsAnd, DL))
return SelectInst::Create(Op,
IsAnd ? V : ConstantInt::getTrue(Op->getType()),
IsAnd ? ConstantInt::getFalse(Op->getType()) : V);
return nullptr;
}

// Canonicalize select with fcmp to fabs(). -0.0 makes this tricky. We need
Expand Down Expand Up @@ -3138,11 +3125,6 @@ Instruction *InstCombinerImpl::foldSelectOfBools(SelectInst &SI) {
return replaceInstUsesWith(SI, Op1);
}

if (auto *Op1SI = dyn_cast<SelectInst>(Op1))
if (auto *I = foldAndOrOfSelectUsingImpliedCond(CondVal, *Op1SI,
/* IsAnd */ IsAnd))
return I;

if (auto *ICmp0 = dyn_cast<ICmpInst>(CondVal))
if (auto *ICmp1 = dyn_cast<ICmpInst>(Op1))
if (auto *V = foldAndOrOfICmps(ICmp0, ICmp1, SI, IsAnd,
Expand Down Expand Up @@ -3643,12 +3625,12 @@ Instruction *InstCombinerImpl::visitSelectInst(SelectInst &SI) {

if (SelectInst *TrueSI = dyn_cast<SelectInst>(TrueVal)) {
if (TrueSI->getCondition()->getType() == CondVal->getType()) {
// select(C, select(C, a, b), c) -> select(C, a, c)
if (TrueSI->getCondition() == CondVal) {
if (SI.getTrueValue() == TrueSI->getTrueValue())
return nullptr;
return replaceOperand(SI, 1, TrueSI->getTrueValue());
}
// Fold nested selects if the inner condition can be implied by the outer
// condition.
if (Value *V = simplifyNestedSelectsUsingImpliedCond(
*TrueSI, CondVal, /*CondIsTrue=*/true, DL))
return replaceOperand(SI, 1, V);

// select(C0, select(C1, a, b), b) -> select(C0&C1, a, b)
// We choose this as normal form to enable folding on the And and
// shortening paths for the values (this helps getUnderlyingObjects() for
Expand All @@ -3663,12 +3645,12 @@ Instruction *InstCombinerImpl::visitSelectInst(SelectInst &SI) {
}
if (SelectInst *FalseSI = dyn_cast<SelectInst>(FalseVal)) {
if (FalseSI->getCondition()->getType() == CondVal->getType()) {
// select(C, a, select(C, b, c)) -> select(C, a, c)
if (FalseSI->getCondition() == CondVal) {
if (SI.getFalseValue() == FalseSI->getFalseValue())
return nullptr;
return replaceOperand(SI, 2, FalseSI->getFalseValue());
}
// Fold nested selects if the inner condition can be implied by the outer
// condition.
if (Value *V = simplifyNestedSelectsUsingImpliedCond(
*FalseSI, CondVal, /*CondIsTrue=*/false, DL))
return replaceOperand(SI, 2, V);

// select(C0, a, select(C1, a, b)) -> select(C0|C1, a, b)
if (FalseSI->getTrueValue() == TrueVal && FalseSI->hasOneUse()) {
Value *Or = Builder.CreateLogicalOr(CondVal, FalseSI->getCondition());
Expand Down
12 changes: 4 additions & 8 deletions ...s/InstCombine/canonicalize-clamp-like-pattern-between-negative-and-positive-thresholds.ll
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Expand Up @@ -189,10 +189,8 @@ define i32 @n9_ult_slt_neg17(i32 %x, i32 %replacement_low, i32 %replacement_high
; Regression test for PR53252.
define i32 @n10_ugt_slt(i32 %x, i32 %replacement_low, i32 %replacement_high) {
; CHECK-LABEL: @n10_ugt_slt(
; CHECK-NEXT: [[T0:%.*]] = icmp slt i32 [[X:%.*]], 0
; CHECK-NEXT: [[T1:%.*]] = select i1 [[T0]], i32 [[REPLACEMENT_LOW:%.*]], i32 [[REPLACEMENT_HIGH:%.*]]
; CHECK-NEXT: [[T2:%.*]] = icmp ugt i32 [[X]], 128
; CHECK-NEXT: [[R:%.*]] = select i1 [[T2]], i32 [[X]], i32 [[T1]]
; CHECK-NEXT: [[T2:%.*]] = icmp ugt i32 [[X:%.*]], 128
; CHECK-NEXT: [[R:%.*]] = select i1 [[T2]], i32 [[X]], i32 [[REPLACEMENT_HIGH:%.*]]
; CHECK-NEXT: ret i32 [[R]]
;
%t0 = icmp slt i32 %x, 0
Expand All @@ -204,10 +202,8 @@ define i32 @n10_ugt_slt(i32 %x, i32 %replacement_low, i32 %replacement_high) {

define i32 @n11_uge_slt(i32 %x, i32 %replacement_low, i32 %replacement_high) {
; CHECK-LABEL: @n11_uge_slt(
; CHECK-NEXT: [[T0:%.*]] = icmp slt i32 [[X:%.*]], 0
; CHECK-NEXT: [[T1:%.*]] = select i1 [[T0]], i32 [[REPLACEMENT_LOW:%.*]], i32 [[REPLACEMENT_HIGH:%.*]]
; CHECK-NEXT: [[T2:%.*]] = icmp ult i32 [[X]], 129
; CHECK-NEXT: [[R:%.*]] = select i1 [[T2]], i32 [[T1]], i32 [[X]]
; CHECK-NEXT: [[T2:%.*]] = icmp ult i32 [[X:%.*]], 129
; CHECK-NEXT: [[R:%.*]] = select i1 [[T2]], i32 [[REPLACEMENT_HIGH:%.*]], i32 [[X]]
; CHECK-NEXT: ret i32 [[R]]
;
%t0 = icmp slt i32 %x, 0
Expand Down
91 changes: 91 additions & 0 deletions llvm/test/Transforms/InstCombine/nested-select.ll
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Expand Up @@ -498,3 +498,94 @@ define i1 @orcond.111.inv.all.conds(i1 %inner.cond, i1 %alt.cond, i1 %inner.sel.
%outer.sel = select i1 %not.outer.cond, i1 true, i1 %inner.sel
ret i1 %outer.sel
}

define i8 @test_implied_true(i8 %x) {
; CHECK-LABEL: @test_implied_true(
; CHECK-NEXT: [[CMP2:%.*]] = icmp slt i8 [[X:%.*]], 0
; CHECK-NEXT: [[SEL2:%.*]] = select i1 [[CMP2]], i8 0, i8 20
; CHECK-NEXT: ret i8 [[SEL2]]
;
%cmp1 = icmp slt i8 %x, 10
%cmp2 = icmp slt i8 %x, 0
%sel1 = select i1 %cmp1, i8 0, i8 5
%sel2 = select i1 %cmp2, i8 %sel1, i8 20
ret i8 %sel2
}

define <2 x i8> @test_implied_true_vec(<2 x i8> %x) {
; CHECK-LABEL: @test_implied_true_vec(
; CHECK-NEXT: [[CMP2:%.*]] = icmp slt <2 x i8> [[X:%.*]], zeroinitializer
; CHECK-NEXT: [[SEL2:%.*]] = select <2 x i1> [[CMP2]], <2 x i8> zeroinitializer, <2 x i8> <i8 20, i8 20>
; CHECK-NEXT: ret <2 x i8> [[SEL2]]
;
%cmp1 = icmp slt <2 x i8> %x, <i8 10, i8 10>
%cmp2 = icmp slt <2 x i8> %x, zeroinitializer
%sel1 = select <2 x i1> %cmp1, <2 x i8> zeroinitializer, <2 x i8> <i8 5, i8 5>
%sel2 = select <2 x i1> %cmp2, <2 x i8> %sel1, <2 x i8> <i8 20, i8 20>
ret <2 x i8> %sel2
}

define i8 @test_implied_true_falseval(i8 %x) {
; CHECK-LABEL: @test_implied_true_falseval(
; CHECK-NEXT: [[CMP2:%.*]] = icmp sgt i8 [[X:%.*]], 0
; CHECK-NEXT: [[SEL2:%.*]] = select i1 [[CMP2]], i8 20, i8 0
; CHECK-NEXT: ret i8 [[SEL2]]
;
%cmp1 = icmp slt i8 %x, 10
%cmp2 = icmp sgt i8 %x, 0
%sel1 = select i1 %cmp1, i8 0, i8 5
%sel2 = select i1 %cmp2, i8 20, i8 %sel1
ret i8 %sel2
}

define i8 @test_implied_false(i8 %x) {
; CHECK-LABEL: @test_implied_false(
; CHECK-NEXT: [[CMP2:%.*]] = icmp slt i8 [[X:%.*]], 0
; CHECK-NEXT: [[SEL2:%.*]] = select i1 [[CMP2]], i8 5, i8 20
; CHECK-NEXT: ret i8 [[SEL2]]
;
%cmp1 = icmp sgt i8 %x, 10
%cmp2 = icmp slt i8 %x, 0
%sel1 = select i1 %cmp1, i8 0, i8 5
%sel2 = select i1 %cmp2, i8 %sel1, i8 20
ret i8 %sel2
}

; Negative tests

define i8 @test_imply_fail(i8 %x) {
; CHECK-LABEL: @test_imply_fail(
; CHECK-NEXT: [[CMP1:%.*]] = icmp slt i8 [[X:%.*]], -10
; CHECK-NEXT: [[CMP2:%.*]] = icmp slt i8 [[X]], 0
; CHECK-NEXT: [[SEL1:%.*]] = select i1 [[CMP1]], i8 0, i8 5
; CHECK-NEXT: [[SEL2:%.*]] = select i1 [[CMP2]], i8 [[SEL1]], i8 20
; CHECK-NEXT: ret i8 [[SEL2]]
;
%cmp1 = icmp slt i8 %x, -10
%cmp2 = icmp slt i8 %x, 0
%sel1 = select i1 %cmp1, i8 0, i8 5
%sel2 = select i1 %cmp2, i8 %sel1, i8 20
ret i8 %sel2
}

define <2 x i8> @test_imply_type_mismatch(<2 x i8> %x, i8 %y) {
; CHECK-LABEL: @test_imply_type_mismatch(
; CHECK-NEXT: [[CMP1:%.*]] = icmp slt <2 x i8> [[X:%.*]], <i8 10, i8 10>
; CHECK-NEXT: [[CMP2:%.*]] = icmp slt i8 [[Y:%.*]], 0
; CHECK-NEXT: [[SEL1:%.*]] = select <2 x i1> [[CMP1]], <2 x i8> zeroinitializer, <2 x i8> <i8 5, i8 5>
; CHECK-NEXT: [[SEL2:%.*]] = select i1 [[CMP2]], <2 x i8> [[SEL1]], <2 x i8> <i8 20, i8 20>
; CHECK-NEXT: ret <2 x i8> [[SEL2]]
;
%cmp1 = icmp slt <2 x i8> %x, <i8 10, i8 10>
%cmp2 = icmp slt i8 %y, 0
%sel1 = select <2 x i1> %cmp1, <2 x i8> zeroinitializer, <2 x i8> <i8 5, i8 5>
%sel2 = select i1 %cmp2, <2 x i8> %sel1, <2 x i8> <i8 20, i8 20>
ret <2 x i8> %sel2
}

define <4 x i1> @test_dont_crash(i1 %cond, <4 x i1> %a, <4 x i1> %b) {
entry:
%sel = select i1 %cond, <4 x i1> %a, <4 x i1> zeroinitializer
%and = and <4 x i1> %sel, %b
ret <4 x i1> %and
}