[llvm] [ValueTracking] Compute known bits of or/and/xor recurrences from start and step (PR #222334)

Konstantin Bogdanov via llvm-commits llvm-commits at lists.llvm.org
Wed Sep 9 13:04:03 PDT 2026


https://github.com/thevar1able updated https://github.com/llvm/llvm-project/pull/222334

>From 3bb3daacc67e5b18f3befed50abb20710c8cb1ac Mon Sep 17 00:00:00 2001
From: Konstantin Bogdanov <konstantin at clickhouse.com>
Date: Wed, 9 Sep 2026 15:44:15 +0200
Subject: [PATCH] [ValueTracking] Compute known bits of or/and/xor recurrences
 from start and step

---
 llvm/lib/Analysis/ValueTracking.cpp           |  16 +-
 .../ValueTracking/phi-known-nonzero.ll        |  71 +++++++
 .../AMDGPU/GlobalISel/is-safe-to-sink-bug.ll  |  21 +-
 llvm/test/CodeGen/AMDGPU/absdiff.ll           |   5 +-
 .../test/Transforms/InstCombine/recurrence.ll | 198 ++++++++++++++++++
 5 files changed, 295 insertions(+), 16 deletions(-)

diff --git a/llvm/lib/Analysis/ValueTracking.cpp b/llvm/lib/Analysis/ValueTracking.cpp
index c881ecc8d2d35..8c29b54ae2ac5 100644
--- a/llvm/lib/Analysis/ValueTracking.cpp
+++ b/llvm/lib/Analysis/ValueTracking.cpp
@@ -1883,6 +1883,7 @@ static void computeKnownBitsFromOperator(const Operator *I,
       case Instruction::Sub:
       case Instruction::And:
       case Instruction::Or:
+      case Instruction::Xor:
       case Instruction::Mul: {
         // Change the context instruction to the "edge" that flows into the
         // phi. This is important because that is where the value is actually
@@ -1907,8 +1908,17 @@ static void computeKnownBitsFromOperator(const Operator *I,
         RecQ.CxtI = LatchTerm;
         computeKnownBits(Step, DemandedElts, KnownStep, RecQ, Depth + 1);
 
-        Known.Zero.setLowBits(std::min(KnownStart.countMinTrailingZeros(),
-                                       KnownStep.countMinTrailingZeros()));
+        if (Opcode == Instruction::Or || Opcode == Instruction::Xor) {
+          Known.Zero |= KnownStart.Zero & KnownStep.Zero;
+          if (Opcode == Instruction::Or)
+            Known.One |= KnownStart.One;
+        } else if (Opcode == Instruction::And) {
+          Known.Zero |= KnownStart.Zero;
+          Known.One |= KnownStart.One & KnownStep.One;
+        } else {
+          Known.Zero.setLowBits(std::min(KnownStart.countMinTrailingZeros(),
+                                         KnownStep.countMinTrailingZeros()));
+        }
 
         auto *OverflowOp = dyn_cast<OverflowingBinaryOperator>(BO);
         if (!OverflowOp || !Q.IIQ.hasNoSignedWrap(OverflowOp))
@@ -3140,6 +3150,8 @@ static bool isNonZeroRecurrence(const PHINode *PN) {
   case Instruction::AShr:
   case Instruction::LShr:
     return BO->isExact();
+  case Instruction::Or:
+    return true;
   default:
     return false;
   }
diff --git a/llvm/test/Analysis/ValueTracking/phi-known-nonzero.ll b/llvm/test/Analysis/ValueTracking/phi-known-nonzero.ll
index d80d1704c73d1..378ab3230eb5d 100644
--- a/llvm/test/Analysis/ValueTracking/phi-known-nonzero.ll
+++ b/llvm/test/Analysis/ValueTracking/phi-known-nonzero.ll
@@ -262,3 +262,74 @@ T:
 F:
   br label %T
 }
+
+; An or recurrence with a non-zero start value is never zero.
+define i1 @or_recurrence_nonzero_start(ptr %p, i64 %n) {
+; CHECK-LABEL: @or_recurrence_nonzero_start(
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    br label [[LOOP:%.*]]
+; CHECK:       loop:
+; CHECK-NEXT:    [[IV:%.*]] = phi i64 [ 0, [[ENTRY:%.*]] ], [ [[IV_NEXT:%.*]], [[LOOP]] ]
+; CHECK-NEXT:    [[ACC:%.*]] = phi i32 [ 32768, [[ENTRY]] ], [ [[ACC_NEXT:%.*]], [[LOOP]] ]
+; CHECK-NEXT:    [[GEP:%.*]] = getelementptr i32, ptr [[P:%.*]], i64 [[IV]]
+; CHECK-NEXT:    [[X:%.*]] = load i32, ptr [[GEP]], align 4
+; CHECK-NEXT:    [[ACC_NEXT]] = or i32 [[X]], [[ACC]]
+; CHECK-NEXT:    [[IV_NEXT]] = add i64 [[IV]], 1
+; CHECK-NEXT:    [[EC:%.*]] = icmp eq i64 [[IV_NEXT]], [[N:%.*]]
+; CHECK-NEXT:    br i1 [[EC]], label [[EXIT:%.*]], label [[LOOP]]
+; CHECK:       exit:
+; CHECK-NEXT:    ret i1 false
+;
+entry:
+  br label %loop
+
+loop:
+  %iv = phi i64 [ 0, %entry ], [ %iv.next, %loop ]
+  %acc = phi i32 [ 32768, %entry ], [ %acc.next, %loop ]
+  %gep = getelementptr i32, ptr %p, i64 %iv
+  %x = load i32, ptr %gep
+  %acc.next = or i32 %x, %acc
+  %iv.next = add i64 %iv, 1
+  %ec = icmp eq i64 %iv.next, %n
+  br i1 %ec, label %exit, label %loop
+
+exit:
+  %cmp = icmp eq i32 %acc.next, 0
+  ret i1 %cmp
+}
+
+; Negative test: the start value is zero.
+define i1 @or_recurrence_zero_start(ptr %p, i64 %n) {
+; CHECK-LABEL: @or_recurrence_zero_start(
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    br label [[LOOP:%.*]]
+; CHECK:       loop:
+; CHECK-NEXT:    [[IV:%.*]] = phi i64 [ 0, [[ENTRY:%.*]] ], [ [[IV_NEXT:%.*]], [[LOOP]] ]
+; CHECK-NEXT:    [[ACC:%.*]] = phi i32 [ 0, [[ENTRY]] ], [ [[ACC_NEXT:%.*]], [[LOOP]] ]
+; CHECK-NEXT:    [[GEP:%.*]] = getelementptr i32, ptr [[P:%.*]], i64 [[IV]]
+; CHECK-NEXT:    [[X:%.*]] = load i32, ptr [[GEP]], align 4
+; CHECK-NEXT:    [[ACC_NEXT]] = or i32 [[X]], [[ACC]]
+; CHECK-NEXT:    [[IV_NEXT]] = add i64 [[IV]], 1
+; CHECK-NEXT:    [[EC:%.*]] = icmp eq i64 [[IV_NEXT]], [[N:%.*]]
+; CHECK-NEXT:    br i1 [[EC]], label [[EXIT:%.*]], label [[LOOP]]
+; CHECK:       exit:
+; CHECK-NEXT:    [[CMP:%.*]] = icmp eq i32 [[ACC_NEXT]], 0
+; CHECK-NEXT:    ret i1 [[CMP]]
+;
+entry:
+  br label %loop
+
+loop:
+  %iv = phi i64 [ 0, %entry ], [ %iv.next, %loop ]
+  %acc = phi i32 [ 0, %entry ], [ %acc.next, %loop ]
+  %gep = getelementptr i32, ptr %p, i64 %iv
+  %x = load i32, ptr %gep
+  %acc.next = or i32 %x, %acc
+  %iv.next = add i64 %iv, 1
+  %ec = icmp eq i64 %iv.next, %n
+  br i1 %ec, label %exit, label %loop
+
+exit:
+  %cmp = icmp eq i32 %acc.next, 0
+  ret i1 %cmp
+}
diff --git a/llvm/test/CodeGen/AMDGPU/GlobalISel/is-safe-to-sink-bug.ll b/llvm/test/CodeGen/AMDGPU/GlobalISel/is-safe-to-sink-bug.ll
index d039334ab63dc..a1ea35304f113 100644
--- a/llvm/test/CodeGen/AMDGPU/GlobalISel/is-safe-to-sink-bug.ll
+++ b/llvm/test/CodeGen/AMDGPU/GlobalISel/is-safe-to-sink-bug.ll
@@ -19,11 +19,11 @@ define amdgpu_ps void @_amdgpu_ps_main(i1 %arg) {
 ; CHECK-NEXT:    s_mov_b32 s2, s0
 ; CHECK-NEXT:    s_mov_b32 s3, s0
 ; CHECK-NEXT:    s_addc_u32 s9, s9, 0
-; CHECK-NEXT:    s_buffer_load_dword s1, s[0:3], 0x0
+; CHECK-NEXT:    s_buffer_load_dword s2, s[0:3], 0x0
 ; CHECK-NEXT:    s_mov_b32 s32, 0
 ; CHECK-NEXT:    v_cmp_ne_u32_e32 vcc_lo, 0, v0
 ; CHECK-NEXT:    s_waitcnt lgkmcnt(0)
-; CHECK-NEXT:    s_cmp_ge_i32 s1, 0
+; CHECK-NEXT:    s_cmp_ge_i32 s2, 0
 ; CHECK-NEXT:    s_cbranch_scc0 .LBB0_2
 ; CHECK-NEXT:  .LBB0_1: ; %bb12
 ; CHECK-NEXT:    v_cndmask_b32_e64 v0, 1.0, 0, s0
@@ -35,23 +35,22 @@ define amdgpu_ps void @_amdgpu_ps_main(i1 %arg) {
 ; CHECK-NEXT:    s_mov_b64 s[2:3], s[10:11]
 ; CHECK-NEXT:    s_swappc_b64 s[30:31], 0
 ; CHECK-NEXT:  .LBB0_2: ; %bb2.preheader
-; CHECK-NEXT:    s_mov_b32 s3, 0
 ; CHECK-NEXT:    s_mov_b32 s1, 0
-; CHECK-NEXT:    s_mov_b32 s2, 0
+; CHECK-NEXT:    s_mov_b32 s3, 0
 ; CHECK-NEXT:    s_branch .LBB0_4
 ; CHECK-NEXT:    .p2align 6
 ; CHECK-NEXT:  .LBB0_3: ; %bb6
 ; CHECK-NEXT:    ; in Loop: Header=BB0_4 Depth=1
 ; CHECK-NEXT:    s_or_b32 exec_lo, exec_lo, s0
 ; CHECK-NEXT:    v_cmp_ne_u32_e64 s0, 0, v0
-; CHECK-NEXT:    s_or_b32 s4, s3, 1
-; CHECK-NEXT:    s_and_b32 s0, s0, s2
-; CHECK-NEXT:    s_cmp_lt_i32 s3, 0
+; CHECK-NEXT:    s_or_b32 s4, s2, 1
+; CHECK-NEXT:    s_and_b32 s0, s0, s3
+; CHECK-NEXT:    s_cmp_lt_i32 s2, 0
 ; CHECK-NEXT:    s_cselect_b32 s5, 1, 0
-; CHECK-NEXT:    s_andn2_b32 s2, s2, exec_lo
+; CHECK-NEXT:    s_andn2_b32 s2, s3, exec_lo
 ; CHECK-NEXT:    s_and_b32 s3, exec_lo, s0
-; CHECK-NEXT:    s_or_b32 s2, s2, s3
-; CHECK-NEXT:    s_mov_b32 s3, s4
+; CHECK-NEXT:    s_or_b32 s3, s2, s3
+; CHECK-NEXT:    s_mov_b32 s2, s4
 ; CHECK-NEXT:    s_cmp_lg_u32 s5, 0
 ; CHECK-NEXT:    s_cbranch_scc0 .LBB0_1
 ; CHECK-NEXT:  .LBB0_4: ; %bb2
@@ -71,7 +70,7 @@ bb:
 
 bb2:
   %i3 = phi i1 [ %i9, %bb6 ], [ false, %bb ]
-  %i4 = phi i32 [ %i10, %bb6 ], [ 0, %bb ]
+  %i4 = phi i32 [ %i10, %bb6 ], [ %i, %bb ]
   br i1 %arg, label %bb5, label %bb6
 
 bb5:
diff --git a/llvm/test/CodeGen/AMDGPU/absdiff.ll b/llvm/test/CodeGen/AMDGPU/absdiff.ll
index e206b4341a096..6670459880ad2 100644
--- a/llvm/test/CodeGen/AMDGPU/absdiff.ll
+++ b/llvm/test/CodeGen/AMDGPU/absdiff.ll
@@ -2,10 +2,9 @@
 ; RUN: llc -mtriple=amdgpu9.00-amd-amdpal < %s | FileCheck %s
 
 
-define amdgpu_gs float @absdiff_valu_input_regression() {
+define amdgpu_gs float @absdiff_valu_input_regression(i32 inreg %start) {
 ; CHECK-LABEL: absdiff_valu_input_regression:
 ; CHECK:       ; %bb.0: ; %bb
-; CHECK-NEXT:    s_mov_b32 s0, 0
 ; CHECK-NEXT:  .LBB0_1: ; %bb1
 ; CHECK-NEXT:    ; =>This Inner Loop Header: Depth=1
 ; CHECK-NEXT:    s_mov_b32 s1, s0
@@ -22,7 +21,7 @@ bb:
   br label %bb1
 
 bb1:                                              ; preds = %bb1, %bb
-  %i = phi i32 [ 0, %bb ], [ %i9, %bb1 ]
+  %i = phi i32 [ %start, %bb ], [ %i9, %bb1 ]
   %i2 = phi i32 [ 0, %bb ], [ %i5, %bb1 ]
   %i3 = or i32 %i2, 1
   %i4 = or i32 %i3, 0
diff --git a/llvm/test/Transforms/InstCombine/recurrence.ll b/llvm/test/Transforms/InstCombine/recurrence.ll
index 456b20a187519..51378af5820ab 100644
--- a/llvm/test/Transforms/InstCombine/recurrence.ll
+++ b/llvm/test/Transforms/InstCombine/recurrence.ll
@@ -199,3 +199,201 @@ exit:
 }
 
 declare void @use(i64)
+
+; The high bits of an or recurrence are known zero if they are zero in both
+; the start value and the step.
+define i32 @test_or_known_zero_high_bits(ptr %p, i64 %n) {
+; CHECK-LABEL: @test_or_known_zero_high_bits(
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    br label [[LOOP:%.*]]
+; CHECK:       loop:
+; CHECK-NEXT:    [[IV:%.*]] = phi i64 [ 0, [[ENTRY:%.*]] ], [ [[IV_NEXT:%.*]], [[LOOP]] ]
+; CHECK-NEXT:    [[ACC:%.*]] = phi i32 [ 0, [[ENTRY]] ], [ [[ACC_NEXT:%.*]], [[LOOP]] ]
+; CHECK-NEXT:    [[GEP:%.*]] = getelementptr inbounds i8, ptr [[P:%.*]], i64 [[IV]]
+; CHECK-NEXT:    [[X:%.*]] = load i8, ptr [[GEP]], align 1
+; CHECK-NEXT:    [[X_EXT:%.*]] = zext i8 [[X]] to i32
+; CHECK-NEXT:    [[ACC_NEXT]] = or i32 [[ACC]], [[X_EXT]]
+; CHECK-NEXT:    [[IV_NEXT]] = add i64 [[IV]], 1
+; CHECK-NEXT:    [[EC:%.*]] = icmp eq i64 [[IV_NEXT]], [[N:%.*]]
+; CHECK-NEXT:    br i1 [[EC]], label [[EXIT:%.*]], label [[LOOP]]
+; CHECK:       exit:
+; CHECK-NEXT:    ret i32 [[ACC_NEXT]]
+;
+entry:
+  br label %loop
+
+loop:
+  %iv = phi i64 [ 0, %entry ], [ %iv.next, %loop ]
+  %acc = phi i32 [ 0, %entry ], [ %acc.next, %loop ]
+  %gep = getelementptr inbounds i8, ptr %p, i64 %iv
+  %x = load i8, ptr %gep
+  %x.ext = zext i8 %x to i32
+  %acc.next = or i32 %acc, %x.ext
+  %iv.next = add i64 %iv, 1
+  %ec = icmp eq i64 %iv.next, %n
+  br i1 %ec, label %exit, label %loop
+
+exit:
+  %masked = and i32 %acc.next, 255
+  ret i32 %masked
+}
+
+; Negative test: the start value has unknown high bits.
+define i32 @test_or_unknown_start(ptr %p, i64 %n, i32 %start) {
+; CHECK-LABEL: @test_or_unknown_start(
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    br label [[LOOP:%.*]]
+; CHECK:       loop:
+; CHECK-NEXT:    [[IV:%.*]] = phi i64 [ 0, [[ENTRY:%.*]] ], [ [[IV_NEXT:%.*]], [[LOOP]] ]
+; CHECK-NEXT:    [[ACC:%.*]] = phi i32 [ [[START:%.*]], [[ENTRY]] ], [ [[ACC_NEXT:%.*]], [[LOOP]] ]
+; CHECK-NEXT:    [[GEP:%.*]] = getelementptr inbounds i8, ptr [[P:%.*]], i64 [[IV]]
+; CHECK-NEXT:    [[X:%.*]] = load i8, ptr [[GEP]], align 1
+; CHECK-NEXT:    [[X_EXT:%.*]] = zext i8 [[X]] to i32
+; CHECK-NEXT:    [[ACC_NEXT]] = or i32 [[ACC]], [[X_EXT]]
+; CHECK-NEXT:    [[IV_NEXT]] = add i64 [[IV]], 1
+; CHECK-NEXT:    [[EC:%.*]] = icmp eq i64 [[IV_NEXT]], [[N:%.*]]
+; CHECK-NEXT:    br i1 [[EC]], label [[EXIT:%.*]], label [[LOOP]]
+; CHECK:       exit:
+; CHECK-NEXT:    [[MASKED:%.*]] = and i32 [[ACC_NEXT]], 255
+; CHECK-NEXT:    ret i32 [[MASKED]]
+;
+entry:
+  br label %loop
+
+loop:
+  %iv = phi i64 [ 0, %entry ], [ %iv.next, %loop ]
+  %acc = phi i32 [ %start, %entry ], [ %acc.next, %loop ]
+  %gep = getelementptr inbounds i8, ptr %p, i64 %iv
+  %x = load i8, ptr %gep
+  %x.ext = zext i8 %x to i32
+  %acc.next = or i32 %acc, %x.ext
+  %iv.next = add i64 %iv, 1
+  %ec = icmp eq i64 %iv.next, %n
+  br i1 %ec, label %exit, label %loop
+
+exit:
+  %masked = and i32 %acc.next, 255
+  ret i32 %masked
+}
+
+; Bits that are one in the start value stay one in an or recurrence, but bits
+; that are only one in the step do not apply to the first iteration.
+define i64 @test_or_known_one_start(i64 %a) {
+; CHECK-LABEL: @test_or_known_one_start(
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    br label [[LOOP:%.*]]
+; CHECK:       loop:
+; CHECK-NEXT:    tail call void @use(i64 1)
+; CHECK-NEXT:    br label [[LOOP]]
+;
+entry:
+  br label %loop
+
+loop:
+  %iv = phi i64 [ 1, %entry ], [ %iv.next, %loop ]
+  %iv.next = or i64 %iv, %a
+  %bit0 = and i64 %iv, 1
+  tail call void @use(i64 %bit0)
+  br label %loop
+}
+
+; The high bits of an and recurrence are known zero if they are zero in the
+; start value.
+define i32 @test_and_known_zero_start(ptr %p, i64 %n) {
+; CHECK-LABEL: @test_and_known_zero_start(
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    br label [[LOOP:%.*]]
+; CHECK:       loop:
+; CHECK-NEXT:    [[IV:%.*]] = phi i64 [ 0, [[ENTRY:%.*]] ], [ [[IV_NEXT:%.*]], [[LOOP]] ]
+; CHECK-NEXT:    [[ACC:%.*]] = phi i32 [ 255, [[ENTRY]] ], [ [[ACC_NEXT:%.*]], [[LOOP]] ]
+; CHECK-NEXT:    [[GEP:%.*]] = getelementptr inbounds [4 x i8], ptr [[P:%.*]], i64 [[IV]]
+; CHECK-NEXT:    [[X:%.*]] = load i32, ptr [[GEP]], align 4
+; CHECK-NEXT:    [[ACC_NEXT]] = and i32 [[ACC]], [[X]]
+; CHECK-NEXT:    [[IV_NEXT]] = add i64 [[IV]], 1
+; CHECK-NEXT:    [[EC:%.*]] = icmp eq i64 [[IV_NEXT]], [[N:%.*]]
+; CHECK-NEXT:    br i1 [[EC]], label [[EXIT:%.*]], label [[LOOP]]
+; CHECK:       exit:
+; CHECK-NEXT:    ret i32 [[ACC_NEXT]]
+;
+entry:
+  br label %loop
+
+loop:
+  %iv = phi i64 [ 0, %entry ], [ %iv.next, %loop ]
+  %acc = phi i32 [ 255, %entry ], [ %acc.next, %loop ]
+  %gep = getelementptr inbounds i32, ptr %p, i64 %iv
+  %x = load i32, ptr %gep
+  %acc.next = and i32 %acc, %x
+  %iv.next = add i64 %iv, 1
+  %ec = icmp eq i64 %iv.next, %n
+  br i1 %ec, label %exit, label %loop
+
+exit:
+  %masked = and i32 %acc.next, 255
+  ret i32 %masked
+}
+
+; Negative test: an and recurrence does not inherit the zero bits of the step,
+; because the step does not apply to the first iteration.
+define i32 @test_and_step_zero_bits(i32 %start) {
+; CHECK-LABEL: @test_and_step_zero_bits(
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    br label [[LOOP:%.*]]
+; CHECK:       loop:
+; CHECK-NEXT:    tail call void @use(i64 0)
+; CHECK-NEXT:    br i1 false, label [[LOOP]], label [[EXIT:%.*]]
+; CHECK:       exit:
+; CHECK-NEXT:    [[MASKED:%.*]] = and i32 [[START:%.*]], 4
+; CHECK-NEXT:    ret i32 [[MASKED]]
+;
+entry:
+  br label %loop
+
+loop:
+  %iv = phi i32 [ %start, %entry ], [ %iv.next, %loop ]
+  %iv.next = and i32 %iv, 4
+  %masked = and i32 %iv, 4
+  tail call void @use(i64 0)
+  br i1 false, label %loop, label %exit
+
+exit:
+  ret i32 %masked
+}
+
+; The high bits of an xor recurrence are known zero if they are zero in both
+; the start value and the step.
+define i32 @test_xor_known_zero_high_bits(ptr %p, i64 %n) {
+; CHECK-LABEL: @test_xor_known_zero_high_bits(
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    br label [[LOOP:%.*]]
+; CHECK:       loop:
+; CHECK-NEXT:    [[IV:%.*]] = phi i64 [ 0, [[ENTRY:%.*]] ], [ [[IV_NEXT:%.*]], [[LOOP]] ]
+; CHECK-NEXT:    [[ACC:%.*]] = phi i32 [ 0, [[ENTRY]] ], [ [[ACC_NEXT:%.*]], [[LOOP]] ]
+; CHECK-NEXT:    [[GEP:%.*]] = getelementptr inbounds i8, ptr [[P:%.*]], i64 [[IV]]
+; CHECK-NEXT:    [[X:%.*]] = load i8, ptr [[GEP]], align 1
+; CHECK-NEXT:    [[X_EXT:%.*]] = zext i8 [[X]] to i32
+; CHECK-NEXT:    [[ACC_NEXT]] = xor i32 [[ACC]], [[X_EXT]]
+; CHECK-NEXT:    [[IV_NEXT]] = add i64 [[IV]], 1
+; CHECK-NEXT:    [[EC:%.*]] = icmp eq i64 [[IV_NEXT]], [[N:%.*]]
+; CHECK-NEXT:    br i1 [[EC]], label [[EXIT:%.*]], label [[LOOP]]
+; CHECK:       exit:
+; CHECK-NEXT:    ret i32 [[ACC_NEXT]]
+;
+entry:
+  br label %loop
+
+loop:
+  %iv = phi i64 [ 0, %entry ], [ %iv.next, %loop ]
+  %acc = phi i32 [ 0, %entry ], [ %acc.next, %loop ]
+  %gep = getelementptr inbounds i8, ptr %p, i64 %iv
+  %x = load i8, ptr %gep
+  %x.ext = zext i8 %x to i32
+  %acc.next = xor i32 %acc, %x.ext
+  %iv.next = add i64 %iv, 1
+  %ec = icmp eq i64 %iv.next, %n
+  br i1 %ec, label %exit, label %loop
+
+exit:
+  %masked = and i32 %acc.next, 255
+  ret i32 %masked
+}



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