[llvm] goldsteinn/op x with x eq 0 (PR #88579)
via llvm-commits
llvm-commits at lists.llvm.org
Fri Apr 12 14:03:49 PDT 2024
https://github.com/goldsteinn created https://github.com/llvm/llvm-project/pull/88579
- **[ValueTracking] Add tests for `isKnowNonZero` of `X op (X != 0)`; NFC**
- **[ValueTracking] Recognize `X op (X != 0)` as non-zero**
>From 17beeb1bc5ee483e1d5d9867e39b5ba5b7455b63 Mon Sep 17 00:00:00 2001
From: Noah Goldstein <goldstein.w.n at gmail.com>
Date: Fri, 12 Apr 2024 15:37:17 -0500
Subject: [PATCH 1/2] [ValueTracking] Add tests for `isKnowNonZero` of `X op (X
!= 0)`; NFC
---
.../Transforms/InstSimplify/known-non-zero.ll | 211 ++++++++++++++++++
1 file changed, 211 insertions(+)
diff --git a/llvm/test/Transforms/InstSimplify/known-non-zero.ll b/llvm/test/Transforms/InstSimplify/known-non-zero.ll
index d9b8f5eed32390..17efb6fa994a81 100644
--- a/llvm/test/Transforms/InstSimplify/known-non-zero.ll
+++ b/llvm/test/Transforms/InstSimplify/known-non-zero.ll
@@ -377,3 +377,214 @@ define <2 x i1> @insert_nonzero_any_idx_fail(<2 x i8> %xx, i8 %yy, i32 %idx) {
%r = icmp eq <2 x i8> %ins, zeroinitializer
ret <2 x i1> %r
}
+
+define i1 @src_x_add_x_eq_0(i8 %x) {
+; CHECK-LABEL: @src_x_add_x_eq_0(
+; CHECK-NEXT: [[X_EQ_0:%.*]] = icmp eq i8 [[X:%.*]], 0
+; CHECK-NEXT: [[Y:%.*]] = zext i1 [[X_EQ_0]] to i8
+; CHECK-NEXT: [[V:%.*]] = add i8 [[X]], [[Y]]
+; CHECK-NEXT: [[R:%.*]] = icmp eq i8 [[V]], 0
+; CHECK-NEXT: ret i1 [[R]]
+;
+ %x_eq_0 = icmp eq i8 %x, 0
+ %y = zext i1 %x_eq_0 to i8
+ %v = add i8 %x, %y
+ %r = icmp eq i8 %v, 0
+ ret i1 %r
+}
+
+define i1 @src_x_add_x_eq_1_fail(i8 %x) {
+; CHECK-LABEL: @src_x_add_x_eq_1_fail(
+; CHECK-NEXT: [[X_EQ_1:%.*]] = icmp eq i8 [[X:%.*]], 1
+; CHECK-NEXT: [[Y:%.*]] = zext i1 [[X_EQ_1]] to i8
+; CHECK-NEXT: [[V:%.*]] = add i8 [[X]], [[Y]]
+; CHECK-NEXT: [[R:%.*]] = icmp eq i8 [[V]], 0
+; CHECK-NEXT: ret i1 [[R]]
+;
+ %x_eq_1 = icmp eq i8 %x, 1
+ %y = zext i1 %x_eq_1 to i8
+ %v = add i8 %x, %y
+ %r = icmp eq i8 %v, 0
+ ret i1 %r
+}
+
+define i1 @src_x_or_x_eq_0(i8 %x) {
+; CHECK-LABEL: @src_x_or_x_eq_0(
+; CHECK-NEXT: [[X_EQ_0:%.*]] = icmp eq i8 [[X:%.*]], 0
+; CHECK-NEXT: [[Y:%.*]] = sext i1 [[X_EQ_0]] to i8
+; CHECK-NEXT: [[V:%.*]] = or i8 [[X]], [[Y]]
+; CHECK-NEXT: [[R:%.*]] = icmp eq i8 [[V]], 0
+; CHECK-NEXT: ret i1 [[R]]
+;
+ %x_eq_0 = icmp eq i8 %x, 0
+ %y = sext i1 %x_eq_0 to i8
+ %v = or i8 %x, %y
+ %r = icmp eq i8 %v, 0
+ ret i1 %r
+}
+
+define i1 @src_x_or_x_sle_0_fail(i8 %x) {
+; CHECK-LABEL: @src_x_or_x_sle_0_fail(
+; CHECK-NEXT: [[X_EQ_0:%.*]] = icmp sle i8 [[X:%.*]], 0
+; CHECK-NEXT: [[Y:%.*]] = sext i1 [[X_EQ_0]] to i8
+; CHECK-NEXT: [[V:%.*]] = or i8 [[X]], [[Y]]
+; CHECK-NEXT: [[R:%.*]] = icmp eq i8 [[V]], 0
+; CHECK-NEXT: ret i1 [[R]]
+;
+ %x_eq_0 = icmp sle i8 %x, 0
+ %y = sext i1 %x_eq_0 to i8
+ %v = or i8 %x, %y
+ %r = icmp eq i8 %v, 0
+ ret i1 %r
+}
+
+define i1 @src_x_xor_x_eq_0(i8 %x) {
+; CHECK-LABEL: @src_x_xor_x_eq_0(
+; CHECK-NEXT: [[X_EQ_0:%.*]] = icmp eq i8 [[X:%.*]], 0
+; CHECK-NEXT: [[Y:%.*]] = zext i1 [[X_EQ_0]] to i8
+; CHECK-NEXT: [[V:%.*]] = xor i8 [[X]], [[Y]]
+; CHECK-NEXT: [[R:%.*]] = icmp eq i8 [[V]], 0
+; CHECK-NEXT: ret i1 [[R]]
+;
+ %x_eq_0 = icmp eq i8 %x, 0
+ %y = zext i1 %x_eq_0 to i8
+ %v = xor i8 %x, %y
+ %r = icmp eq i8 %v, 0
+ ret i1 %r
+}
+
+define i1 @src_x_xor_x_ne_0_fail(i8 %x) {
+; CHECK-LABEL: @src_x_xor_x_ne_0_fail(
+; CHECK-NEXT: [[X_NE_0:%.*]] = icmp ne i8 [[X:%.*]], 0
+; CHECK-NEXT: [[Y:%.*]] = zext i1 [[X_NE_0]] to i8
+; CHECK-NEXT: [[V:%.*]] = xor i8 [[X]], [[Y]]
+; CHECK-NEXT: [[R:%.*]] = icmp eq i8 [[V]], 0
+; CHECK-NEXT: ret i1 [[R]]
+;
+ %x_ne_0 = icmp ne i8 %x, 0
+ %y = zext i1 %x_ne_0 to i8
+ %v = xor i8 %x, %y
+ %r = icmp eq i8 %v, 0
+ ret i1 %r
+}
+
+define i1 @src_x_sub0_x_eq_0(i8 %x) {
+; CHECK-LABEL: @src_x_sub0_x_eq_0(
+; CHECK-NEXT: [[X_EQ_0:%.*]] = icmp eq i8 [[X:%.*]], 0
+; CHECK-NEXT: [[Y:%.*]] = sext i1 [[X_EQ_0]] to i8
+; CHECK-NEXT: [[V:%.*]] = sub i8 [[X]], [[Y]]
+; CHECK-NEXT: [[R:%.*]] = icmp eq i8 [[V]], 0
+; CHECK-NEXT: ret i1 [[R]]
+;
+ %x_eq_0 = icmp eq i8 %x, 0
+ %y = sext i1 %x_eq_0 to i8
+ %v = sub i8 %x, %y
+ %r = icmp eq i8 %v, 0
+ ret i1 %r
+}
+
+define i1 @src_x_sub0_z_eq_0_fail(i8 %x, i8 %z) {
+; CHECK-LABEL: @src_x_sub0_z_eq_0_fail(
+; CHECK-NEXT: [[Z_EQ_0:%.*]] = icmp eq i8 [[Z:%.*]], 0
+; CHECK-NEXT: [[Y:%.*]] = sext i1 [[Z_EQ_0]] to i8
+; CHECK-NEXT: [[V:%.*]] = sub i8 [[X:%.*]], [[Y]]
+; CHECK-NEXT: [[R:%.*]] = icmp eq i8 [[V]], 0
+; CHECK-NEXT: ret i1 [[R]]
+;
+ %z_eq_0 = icmp eq i8 %z, 0
+ %y = sext i1 %z_eq_0 to i8
+ %v = sub i8 %x, %y
+ %r = icmp eq i8 %v, 0
+ ret i1 %r
+}
+
+define i1 @src_x_sub1_x_eq_0(i8 %x) {
+; CHECK-LABEL: @src_x_sub1_x_eq_0(
+; CHECK-NEXT: [[X_EQ_0:%.*]] = icmp eq i8 [[X:%.*]], 0
+; CHECK-NEXT: [[Y:%.*]] = zext i1 [[X_EQ_0]] to i8
+; CHECK-NEXT: [[V:%.*]] = sub i8 [[Y]], [[X]]
+; CHECK-NEXT: [[R:%.*]] = icmp eq i8 [[V]], 0
+; CHECK-NEXT: ret i1 [[R]]
+;
+ %x_eq_0 = icmp eq i8 %x, 0
+ %y = zext i1 %x_eq_0 to i8
+ %v = sub i8 %y, %x
+ %r = icmp eq i8 %v, 0
+ ret i1 %r
+}
+
+define i1 @src_x_sub1_x_eq_0_or_fail(i8 %x, i1 %c1) {
+; CHECK-LABEL: @src_x_sub1_x_eq_0_or_fail(
+; CHECK-NEXT: [[X_EQ_0:%.*]] = icmp eq i8 [[X:%.*]], 0
+; CHECK-NEXT: [[X_EQ_0_OR:%.*]] = or i1 [[X_EQ_0]], [[C1:%.*]]
+; CHECK-NEXT: [[Y:%.*]] = zext i1 [[X_EQ_0_OR]] to i8
+; CHECK-NEXT: [[V:%.*]] = sub i8 [[Y]], [[X]]
+; CHECK-NEXT: [[R:%.*]] = icmp eq i8 [[V]], 0
+; CHECK-NEXT: ret i1 [[R]]
+;
+ %x_eq_0 = icmp eq i8 %x, 0
+ %x_eq_0_or = or i1 %x_eq_0, %c1
+ %y = zext i1 %x_eq_0_or to i8
+ %v = sub i8 %y, %x
+ %r = icmp eq i8 %v, 0
+ ret i1 %r
+}
+
+define i1 @src_x_umax_x_eq_0(i8 %x) {
+; CHECK-LABEL: @src_x_umax_x_eq_0(
+; CHECK-NEXT: [[X_EQ_0:%.*]] = icmp eq i8 [[X:%.*]], 0
+; CHECK-NEXT: [[Y:%.*]] = sext i1 [[X_EQ_0]] to i8
+; CHECK-NEXT: [[V:%.*]] = call i8 @llvm.umax.i8(i8 [[Y]], i8 [[X]])
+; CHECK-NEXT: [[R:%.*]] = icmp eq i8 [[V]], 0
+; CHECK-NEXT: ret i1 [[R]]
+;
+ %x_eq_0 = icmp eq i8 %x, 0
+ %y = sext i1 %x_eq_0 to i8
+ %v = call i8 @llvm.umax.i8(i8 %y, i8 %x)
+ %r = icmp eq i8 %v, 0
+ ret i1 %r
+}
+
+define i1 @src_x_umax_x_ugt_10_fail(i8 %x) {
+; CHECK-LABEL: @src_x_umax_x_ugt_10_fail(
+; CHECK-NEXT: [[X_UGT_10:%.*]] = icmp ugt i8 [[X:%.*]], 10
+; CHECK-NEXT: [[Y:%.*]] = sext i1 [[X_UGT_10]] to i8
+; CHECK-NEXT: [[V:%.*]] = call i8 @llvm.umax.i8(i8 [[Y]], i8 [[X]])
+; CHECK-NEXT: [[R:%.*]] = icmp eq i8 [[V]], 0
+; CHECK-NEXT: ret i1 [[R]]
+;
+ %x_ugt_10 = icmp ugt i8 %x, 10
+ %y = sext i1 %x_ugt_10 to i8
+ %v = call i8 @llvm.umax.i8(i8 %y, i8 %x)
+ %r = icmp eq i8 %v, 0
+ ret i1 %r
+}
+
+define i1 @src_x_uadd.sat_x_eq_0(i8 %x) {
+; CHECK-LABEL: @src_x_uadd.sat_x_eq_0(
+; CHECK-NEXT: [[X_EQ_0:%.*]] = icmp eq i8 [[X:%.*]], 0
+; CHECK-NEXT: [[Y:%.*]] = zext i1 [[X_EQ_0]] to i8
+; CHECK-NEXT: [[V:%.*]] = call i8 @llvm.uadd.sat.i8(i8 [[Y]], i8 [[X]])
+; CHECK-NEXT: [[R:%.*]] = icmp eq i8 [[V]], 0
+; CHECK-NEXT: ret i1 [[R]]
+;
+ %x_eq_0 = icmp eq i8 %x, 0
+ %y = zext i1 %x_eq_0 to i8
+ %v = call i8 @llvm.uadd.sat.i8(i8 %y, i8 %x)
+ %r = icmp eq i8 %v, 0
+ ret i1 %r
+}
+
+define i1 @src_x_uadd.sat_c1_fail(i8 %x, i1 %c1) {
+; CHECK-LABEL: @src_x_uadd.sat_c1_fail(
+; CHECK-NEXT: [[Y:%.*]] = zext i1 [[C1:%.*]] to i8
+; CHECK-NEXT: [[V:%.*]] = call i8 @llvm.uadd.sat.i8(i8 [[Y]], i8 [[X:%.*]])
+; CHECK-NEXT: [[R:%.*]] = icmp eq i8 [[V]], 0
+; CHECK-NEXT: ret i1 [[R]]
+;
+ %y = zext i1 %c1 to i8
+ %v = call i8 @llvm.uadd.sat.i8(i8 %y, i8 %x)
+ %r = icmp eq i8 %v, 0
+ ret i1 %r
+}
+
>From a756fcedc5c8f943bb28c5df92cb60d0a52a6c78 Mon Sep 17 00:00:00 2001
From: Noah Goldstein <goldstein.w.n at gmail.com>
Date: Fri, 12 Apr 2024 15:55:52 -0500
Subject: [PATCH 2/2] [ValueTracking] Recognize `X op (X != 0)` as non-zero
The ops supported are: `add`, `sub`, `xor`, `or`, `umax`, `uadd.sat`
Proofs: https://alive2.llvm.org/ce/z/8ZMSRg
The `add` case actually comes up in SPECInt, the rest are here mostly
for completeness.
---
llvm/lib/Analysis/ValueTracking.cpp | 29 +++++++++++++
.../Transforms/InstSimplify/known-non-zero.ll | 42 ++++---------------
2 files changed, 36 insertions(+), 35 deletions(-)
diff --git a/llvm/lib/Analysis/ValueTracking.cpp b/llvm/lib/Analysis/ValueTracking.cpp
index b83e7e6769c200..e25f2f99a69950 100644
--- a/llvm/lib/Analysis/ValueTracking.cpp
+++ b/llvm/lib/Analysis/ValueTracking.cpp
@@ -2420,9 +2420,20 @@ static bool isNonZeroRecurrence(const PHINode *PN) {
}
}
+static bool matchOpWithOpEqZero(Value *Op0, Value *Op1) {
+ ICmpInst::Predicate Pred;
+ return (match(Op0, m_ZExtOrSExt(m_ICmp(Pred, m_Specific(Op1), m_Zero()))) ||
+ match(Op1, m_ZExtOrSExt(m_ICmp(Pred, m_Specific(Op0), m_Zero())))) &&
+ Pred == ICmpInst::ICMP_EQ;
+}
+
static bool isNonZeroAdd(const APInt &DemandedElts, unsigned Depth,
const SimplifyQuery &Q, unsigned BitWidth, Value *X,
Value *Y, bool NSW, bool NUW) {
+ // (X + (X != 0)) is non zero
+ if (matchOpWithOpEqZero(X, Y))
+ return true;
+
if (NUW)
return isKnownNonZero(Y, DemandedElts, Depth, Q) ||
isKnownNonZero(X, DemandedElts, Depth, Q);
@@ -2466,6 +2477,11 @@ static bool isNonZeroAdd(const APInt &DemandedElts, unsigned Depth,
static bool isNonZeroSub(const APInt &DemandedElts, unsigned Depth,
const SimplifyQuery &Q, unsigned BitWidth, Value *X,
Value *Y) {
+ // (X - (X != 0)) is non zero
+ // ((X != 0) - X) is non zero
+ if (matchOpWithOpEqZero(X, Y))
+ return true;
+
// TODO: Move this case into isKnownNonEqual().
if (auto *C = dyn_cast<Constant>(X))
if (C->isNullValue() && isKnownNonZero(Y, DemandedElts, Depth, Q))
@@ -2618,7 +2634,15 @@ static bool isKnownNonZeroFromOperator(const Operator *I,
case Instruction::Sub:
return isNonZeroSub(DemandedElts, Depth, Q, BitWidth, I->getOperand(0),
I->getOperand(1));
+ case Instruction::Xor:
+ // (X ^ (X != 0)) is non zero
+ if (matchOpWithOpEqZero(I->getOperand(0), I->getOperand(1)))
+ return true;
+ break;
case Instruction::Or:
+ // (X | (X != 0)) is non zero
+ if (matchOpWithOpEqZero(I->getOperand(0), I->getOperand(1)))
+ return true;
// X | Y != 0 if X != 0 or Y != 0.
return isKnownNonZero(I->getOperand(1), DemandedElts, Depth, Q) ||
isKnownNonZero(I->getOperand(0), DemandedElts, Depth, Q);
@@ -2909,6 +2933,11 @@ static bool isKnownNonZeroFromOperator(const Operator *I,
return isKnownNonZero(II->getArgOperand(0), Depth, Q);
case Intrinsic::umax:
case Intrinsic::uadd_sat:
+ // umax(X, (X != 0)) is non zero
+ // X +usat (X != 0) is non zero
+ if (matchOpWithOpEqZero(II->getArgOperand(0), II->getArgOperand(1)))
+ return true;
+
return isKnownNonZero(II->getArgOperand(1), DemandedElts, Depth, Q) ||
isKnownNonZero(II->getArgOperand(0), DemandedElts, Depth, Q);
case Intrinsic::smax: {
diff --git a/llvm/test/Transforms/InstSimplify/known-non-zero.ll b/llvm/test/Transforms/InstSimplify/known-non-zero.ll
index 17efb6fa994a81..f39c4cc7f59933 100644
--- a/llvm/test/Transforms/InstSimplify/known-non-zero.ll
+++ b/llvm/test/Transforms/InstSimplify/known-non-zero.ll
@@ -380,11 +380,7 @@ define <2 x i1> @insert_nonzero_any_idx_fail(<2 x i8> %xx, i8 %yy, i32 %idx) {
define i1 @src_x_add_x_eq_0(i8 %x) {
; CHECK-LABEL: @src_x_add_x_eq_0(
-; CHECK-NEXT: [[X_EQ_0:%.*]] = icmp eq i8 [[X:%.*]], 0
-; CHECK-NEXT: [[Y:%.*]] = zext i1 [[X_EQ_0]] to i8
-; CHECK-NEXT: [[V:%.*]] = add i8 [[X]], [[Y]]
-; CHECK-NEXT: [[R:%.*]] = icmp eq i8 [[V]], 0
-; CHECK-NEXT: ret i1 [[R]]
+; CHECK-NEXT: ret i1 false
;
%x_eq_0 = icmp eq i8 %x, 0
%y = zext i1 %x_eq_0 to i8
@@ -410,11 +406,7 @@ define i1 @src_x_add_x_eq_1_fail(i8 %x) {
define i1 @src_x_or_x_eq_0(i8 %x) {
; CHECK-LABEL: @src_x_or_x_eq_0(
-; CHECK-NEXT: [[X_EQ_0:%.*]] = icmp eq i8 [[X:%.*]], 0
-; CHECK-NEXT: [[Y:%.*]] = sext i1 [[X_EQ_0]] to i8
-; CHECK-NEXT: [[V:%.*]] = or i8 [[X]], [[Y]]
-; CHECK-NEXT: [[R:%.*]] = icmp eq i8 [[V]], 0
-; CHECK-NEXT: ret i1 [[R]]
+; CHECK-NEXT: ret i1 false
;
%x_eq_0 = icmp eq i8 %x, 0
%y = sext i1 %x_eq_0 to i8
@@ -440,11 +432,7 @@ define i1 @src_x_or_x_sle_0_fail(i8 %x) {
define i1 @src_x_xor_x_eq_0(i8 %x) {
; CHECK-LABEL: @src_x_xor_x_eq_0(
-; CHECK-NEXT: [[X_EQ_0:%.*]] = icmp eq i8 [[X:%.*]], 0
-; CHECK-NEXT: [[Y:%.*]] = zext i1 [[X_EQ_0]] to i8
-; CHECK-NEXT: [[V:%.*]] = xor i8 [[X]], [[Y]]
-; CHECK-NEXT: [[R:%.*]] = icmp eq i8 [[V]], 0
-; CHECK-NEXT: ret i1 [[R]]
+; CHECK-NEXT: ret i1 false
;
%x_eq_0 = icmp eq i8 %x, 0
%y = zext i1 %x_eq_0 to i8
@@ -470,11 +458,7 @@ define i1 @src_x_xor_x_ne_0_fail(i8 %x) {
define i1 @src_x_sub0_x_eq_0(i8 %x) {
; CHECK-LABEL: @src_x_sub0_x_eq_0(
-; CHECK-NEXT: [[X_EQ_0:%.*]] = icmp eq i8 [[X:%.*]], 0
-; CHECK-NEXT: [[Y:%.*]] = sext i1 [[X_EQ_0]] to i8
-; CHECK-NEXT: [[V:%.*]] = sub i8 [[X]], [[Y]]
-; CHECK-NEXT: [[R:%.*]] = icmp eq i8 [[V]], 0
-; CHECK-NEXT: ret i1 [[R]]
+; CHECK-NEXT: ret i1 false
;
%x_eq_0 = icmp eq i8 %x, 0
%y = sext i1 %x_eq_0 to i8
@@ -500,11 +484,7 @@ define i1 @src_x_sub0_z_eq_0_fail(i8 %x, i8 %z) {
define i1 @src_x_sub1_x_eq_0(i8 %x) {
; CHECK-LABEL: @src_x_sub1_x_eq_0(
-; CHECK-NEXT: [[X_EQ_0:%.*]] = icmp eq i8 [[X:%.*]], 0
-; CHECK-NEXT: [[Y:%.*]] = zext i1 [[X_EQ_0]] to i8
-; CHECK-NEXT: [[V:%.*]] = sub i8 [[Y]], [[X]]
-; CHECK-NEXT: [[R:%.*]] = icmp eq i8 [[V]], 0
-; CHECK-NEXT: ret i1 [[R]]
+; CHECK-NEXT: ret i1 false
;
%x_eq_0 = icmp eq i8 %x, 0
%y = zext i1 %x_eq_0 to i8
@@ -532,11 +512,7 @@ define i1 @src_x_sub1_x_eq_0_or_fail(i8 %x, i1 %c1) {
define i1 @src_x_umax_x_eq_0(i8 %x) {
; CHECK-LABEL: @src_x_umax_x_eq_0(
-; CHECK-NEXT: [[X_EQ_0:%.*]] = icmp eq i8 [[X:%.*]], 0
-; CHECK-NEXT: [[Y:%.*]] = sext i1 [[X_EQ_0]] to i8
-; CHECK-NEXT: [[V:%.*]] = call i8 @llvm.umax.i8(i8 [[Y]], i8 [[X]])
-; CHECK-NEXT: [[R:%.*]] = icmp eq i8 [[V]], 0
-; CHECK-NEXT: ret i1 [[R]]
+; CHECK-NEXT: ret i1 false
;
%x_eq_0 = icmp eq i8 %x, 0
%y = sext i1 %x_eq_0 to i8
@@ -562,11 +538,7 @@ define i1 @src_x_umax_x_ugt_10_fail(i8 %x) {
define i1 @src_x_uadd.sat_x_eq_0(i8 %x) {
; CHECK-LABEL: @src_x_uadd.sat_x_eq_0(
-; CHECK-NEXT: [[X_EQ_0:%.*]] = icmp eq i8 [[X:%.*]], 0
-; CHECK-NEXT: [[Y:%.*]] = zext i1 [[X_EQ_0]] to i8
-; CHECK-NEXT: [[V:%.*]] = call i8 @llvm.uadd.sat.i8(i8 [[Y]], i8 [[X]])
-; CHECK-NEXT: [[R:%.*]] = icmp eq i8 [[V]], 0
-; CHECK-NEXT: ret i1 [[R]]
+; CHECK-NEXT: ret i1 false
;
%x_eq_0 = icmp eq i8 %x, 0
%y = zext i1 %x_eq_0 to i8
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