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[msan] Sharpen instrumentation of Intrinsic::{ctlz,cttz} #145609

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Jun 25, 2025
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[msan] Sharpen instrumentation of Intrinsic::{ctlz,cttz} #145609

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13736a6
[msan] Sharpen instrumentation of Intrinsic::{ctlz,cttz}
thurstond Jun 24, 2025
3cee7d1
Add comment about possible further improvement
thurstond Jun 24, 2025
358dc26
Typo
thurstond Jun 24, 2025
3656c9e
Remove stray change
thurstond Jun 24, 2025
23e3b65
Clarify little-endian (and ctlz)
thurstond Jun 25, 2025
fb7c2a7
Clarify zero-poison comment
thurstond Jun 25, 2025
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41 changes: 34 additions & 7 deletions llvm/lib/Transforms/Instrumentation/MemorySanitizer.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -3278,22 +3278,49 @@ struct MemorySanitizerVisitor : public InstVisitor<MemorySanitizerVisitor> {
setOrigin(&I, getOrigin(Op));
}

void handleCountZeroes(IntrinsicInst &I) {
// Uninitialized bits are ok if they appear after the leading/trailing 0's
// and a 1. If the input is all zero, it is fully initialized iff
// !is_zero_poison.
//
// e.g., if 0/1 are initialized bits with concrete value 0/1, and ? is an
// uninitialized bit:
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for completeness, note that this is little nedian?

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Done

// - 0001 0??? is fully initialized
// - 000? ???? is fully uninitialized (*)
// - ???? ???? is fully uninitialized
// - 0000 0000 is fully initialized iff !is_zero_poison
// (*) TODO: arguably, since the number of zeros is in the range [3, 8], we
// only need to poison 4 bits.
//
// OutputShadow =
// ((ConcreteZerosCount >= ShadowZerosCount) && !AllZeroShadow)
// || (is_zero_poison && AllZeroSrc)
void handleCountLeadingTrailingZeros(IntrinsicInst &I) {
IRBuilder<> IRB(&I);
Value *Src = I.getArgOperand(0);
Value *SrcShadow = getShadow(Src);

Value *False = IRB.getInt1(false);
Value *ConcreteZerosCount = IRB.CreateIntrinsic(
I.getType(), I.getIntrinsicID(), {Src, /*is_zero_poison=*/False});
Value *ShadowZerosCount = IRB.CreateIntrinsic(
I.getType(), I.getIntrinsicID(), {SrcShadow, /*is_zero_poison=*/False});

// Set the Output shadow based on input Shadow
Value *BoolShadow = IRB.CreateIsNotNull(getShadow(Src), "_mscz_bs");
Value *CompareConcreteZeros = IRB.CreateICmpUGE(
ConcreteZerosCount, ShadowZerosCount, "_mscz_cmp_zeros");

Value *NotAllZeroShadow =
IRB.CreateIsNotNull(SrcShadow, "_mscz_shadow_not_null");
Value *OutputShadow =
IRB.CreateAnd(CompareConcreteZeros, NotAllZeroShadow, "_mscz_main");

// If zero poison is requested, mix in with the shadow
Constant *IsZeroPoison = cast<Constant>(I.getOperand(1));
if (!IsZeroPoison->isZeroValue()) {
Value *BoolZeroPoison = IRB.CreateIsNull(Src, "_mscz_bzp");
BoolShadow = IRB.CreateOr(BoolShadow, BoolZeroPoison, "_mscz_bs");
OutputShadow = IRB.CreateOr(OutputShadow, BoolZeroPoison, "_mscz_bs");
}

Value *OutputShadow =
IRB.CreateSExt(BoolShadow, getShadowTy(Src), "_mscz_os");
OutputShadow = IRB.CreateSExt(OutputShadow, getShadowTy(Src), "_mscz_os");

setShadow(&I, OutputShadow);
setOriginForNaryOp(I);
Expand Down Expand Up @@ -4710,7 +4737,7 @@ struct MemorySanitizerVisitor : public InstVisitor<MemorySanitizerVisitor> {
break;
case Intrinsic::ctlz:
case Intrinsic::cttz:
handleCountZeroes(I);
handleCountLeadingTrailingZeros(I);
break;
case Intrinsic::masked_compressstore:
handleMaskedCompressStore(I);
Expand Down
88 changes: 60 additions & 28 deletions llvm/test/Instrumentation/MemorySanitizer/count-zeroes.ll
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Expand Up @@ -9,10 +9,14 @@ define i64 @test_ctlz_i64_zeropoison(i64 %v) #0 {
; CHECK-LABEL: @test_ctlz_i64_zeropoison(
; CHECK-NEXT: [[TMP1:%.*]] = load i64, ptr @__msan_param_tls, align 8
; CHECK-NEXT: call void @llvm.donothing()
; CHECK-NEXT: [[_MSCZ_BS:%.*]] = icmp ne i64 [[TMP1]], 0
; CHECK-NEXT: [[_MSCZ_BZP:%.*]] = icmp eq i64 [[V:%.*]], 0
; CHECK-NEXT: [[_MSCZ_BS1:%.*]] = or i1 [[_MSCZ_BS]], [[_MSCZ_BZP]]
; CHECK-NEXT: [[_MSCZ_OS:%.*]] = sext i1 [[_MSCZ_BS1]] to i64
; CHECK-NEXT: [[TMP2:%.*]] = call i64 @llvm.ctlz.i64(i64 [[V:%.*]], i1 false)
; CHECK-NEXT: [[TMP3:%.*]] = call i64 @llvm.ctlz.i64(i64 [[TMP1]], i1 false)
; CHECK-NEXT: [[_MSCZ_CMP_ZEROS:%.*]] = icmp uge i64 [[TMP2]], [[TMP3]]
; CHECK-NEXT: [[_MSCZ_SHADOW_NOT_NULL:%.*]] = icmp ne i64 [[TMP1]], 0
; CHECK-NEXT: [[_MSCZ_MAIN:%.*]] = and i1 [[_MSCZ_CMP_ZEROS]], [[_MSCZ_SHADOW_NOT_NULL]]
; CHECK-NEXT: [[_MSCZ_BZP:%.*]] = icmp eq i64 [[V]], 0
; CHECK-NEXT: [[_MSCZ_BS:%.*]] = or i1 [[_MSCZ_MAIN]], [[_MSCZ_BZP]]
; CHECK-NEXT: [[_MSCZ_OS:%.*]] = sext i1 [[_MSCZ_BS]] to i64
; CHECK-NEXT: [[RES:%.*]] = call i64 @llvm.ctlz.i64(i64 [[V]], i1 true)
; CHECK-NEXT: store i64 [[_MSCZ_OS]], ptr @__msan_retval_tls, align 8
; CHECK-NEXT: ret i64 [[RES]]
Expand All @@ -24,9 +28,13 @@ define i64 @test_ctlz_i64_nozeropoison(i64 %v) #0 {
; CHECK-LABEL: @test_ctlz_i64_nozeropoison(
; CHECK-NEXT: [[TMP1:%.*]] = load i64, ptr @__msan_param_tls, align 8
; CHECK-NEXT: call void @llvm.donothing()
; CHECK-NEXT: [[_MSCZ_BS:%.*]] = icmp ne i64 [[TMP1]], 0
; CHECK-NEXT: [[_MSCZ_OS:%.*]] = sext i1 [[_MSCZ_BS]] to i64
; CHECK-NEXT: [[RES:%.*]] = call i64 @llvm.ctlz.i64(i64 [[V:%.*]], i1 false)
; CHECK-NEXT: [[TMP2:%.*]] = call i64 @llvm.ctlz.i64(i64 [[V:%.*]], i1 false)
; CHECK-NEXT: [[TMP3:%.*]] = call i64 @llvm.ctlz.i64(i64 [[TMP1]], i1 false)
; CHECK-NEXT: [[_MSCZ_CMP_ZEROS:%.*]] = icmp uge i64 [[TMP2]], [[TMP3]]
; CHECK-NEXT: [[_MSCZ_SHADOW_NOT_NULL:%.*]] = icmp ne i64 [[TMP1]], 0
; CHECK-NEXT: [[_MSCZ_MAIN:%.*]] = and i1 [[_MSCZ_CMP_ZEROS]], [[_MSCZ_SHADOW_NOT_NULL]]
; CHECK-NEXT: [[_MSCZ_OS:%.*]] = sext i1 [[_MSCZ_MAIN]] to i64
; CHECK-NEXT: [[RES:%.*]] = call i64 @llvm.ctlz.i64(i64 [[V]], i1 false)
; CHECK-NEXT: store i64 [[_MSCZ_OS]], ptr @__msan_retval_tls, align 8
; CHECK-NEXT: ret i64 [[RES]]
;
Expand All @@ -39,10 +47,14 @@ define <2 x i64> @test_ctlz_v2i64_zeropoison(<2 x i64> %v) #0 {
; CHECK-LABEL: @test_ctlz_v2i64_zeropoison(
; CHECK-NEXT: [[TMP1:%.*]] = load <2 x i64>, ptr @__msan_param_tls, align 8
; CHECK-NEXT: call void @llvm.donothing()
; CHECK-NEXT: [[_MSCZ_BS:%.*]] = icmp ne <2 x i64> [[TMP1]], zeroinitializer
; CHECK-NEXT: [[_MSCZ_BZP:%.*]] = icmp eq <2 x i64> [[V:%.*]], zeroinitializer
; CHECK-NEXT: [[_MSCZ_BS1:%.*]] = or <2 x i1> [[_MSCZ_BS]], [[_MSCZ_BZP]]
; CHECK-NEXT: [[_MSCZ_OS:%.*]] = sext <2 x i1> [[_MSCZ_BS1]] to <2 x i64>
; CHECK-NEXT: [[TMP2:%.*]] = call <2 x i64> @llvm.ctlz.v2i64(<2 x i64> [[V:%.*]], i1 false)
; CHECK-NEXT: [[TMP3:%.*]] = call <2 x i64> @llvm.ctlz.v2i64(<2 x i64> [[TMP1]], i1 false)
; CHECK-NEXT: [[_MSCZ_CMP_ZEROS:%.*]] = icmp uge <2 x i64> [[TMP2]], [[TMP3]]
; CHECK-NEXT: [[_MSCZ_SHADOW_NOT_NULL:%.*]] = icmp ne <2 x i64> [[TMP1]], zeroinitializer
; CHECK-NEXT: [[_MSCZ_MAIN:%.*]] = and <2 x i1> [[_MSCZ_CMP_ZEROS]], [[_MSCZ_SHADOW_NOT_NULL]]
; CHECK-NEXT: [[_MSCZ_BZP:%.*]] = icmp eq <2 x i64> [[V]], zeroinitializer
; CHECK-NEXT: [[_MSCZ_BS:%.*]] = or <2 x i1> [[_MSCZ_MAIN]], [[_MSCZ_BZP]]
; CHECK-NEXT: [[_MSCZ_OS:%.*]] = sext <2 x i1> [[_MSCZ_BS]] to <2 x i64>
; CHECK-NEXT: [[RES:%.*]] = call <2 x i64> @llvm.ctlz.v2i64(<2 x i64> [[V]], i1 true)
; CHECK-NEXT: store <2 x i64> [[_MSCZ_OS]], ptr @__msan_retval_tls, align 8
; CHECK-NEXT: ret <2 x i64> [[RES]]
Expand All @@ -54,9 +66,13 @@ define <2 x i64> @test_ctlz_v2i64_nozeropoison(<2 x i64> %v) #0 {
; CHECK-LABEL: @test_ctlz_v2i64_nozeropoison(
; CHECK-NEXT: [[TMP1:%.*]] = load <2 x i64>, ptr @__msan_param_tls, align 8
; CHECK-NEXT: call void @llvm.donothing()
; CHECK-NEXT: [[_MSCZ_BS:%.*]] = icmp ne <2 x i64> [[TMP1]], zeroinitializer
; CHECK-NEXT: [[_MSCZ_OS:%.*]] = sext <2 x i1> [[_MSCZ_BS]] to <2 x i64>
; CHECK-NEXT: [[RES:%.*]] = call <2 x i64> @llvm.ctlz.v2i64(<2 x i64> [[V:%.*]], i1 false)
; CHECK-NEXT: [[TMP2:%.*]] = call <2 x i64> @llvm.ctlz.v2i64(<2 x i64> [[V:%.*]], i1 false)
; CHECK-NEXT: [[TMP3:%.*]] = call <2 x i64> @llvm.ctlz.v2i64(<2 x i64> [[TMP1]], i1 false)
; CHECK-NEXT: [[_MSCZ_CMP_ZEROS:%.*]] = icmp uge <2 x i64> [[TMP2]], [[TMP3]]
; CHECK-NEXT: [[_MSCZ_SHADOW_NOT_NULL:%.*]] = icmp ne <2 x i64> [[TMP1]], zeroinitializer
; CHECK-NEXT: [[_MSCZ_MAIN:%.*]] = and <2 x i1> [[_MSCZ_CMP_ZEROS]], [[_MSCZ_SHADOW_NOT_NULL]]
; CHECK-NEXT: [[_MSCZ_OS:%.*]] = sext <2 x i1> [[_MSCZ_MAIN]] to <2 x i64>
; CHECK-NEXT: [[RES:%.*]] = call <2 x i64> @llvm.ctlz.v2i64(<2 x i64> [[V]], i1 false)
; CHECK-NEXT: store <2 x i64> [[_MSCZ_OS]], ptr @__msan_retval_tls, align 8
; CHECK-NEXT: ret <2 x i64> [[RES]]
;
Expand All @@ -69,10 +85,14 @@ define i64 @test_cttz_i64_zeropoison(i64 %v) #0 {
; CHECK-LABEL: @test_cttz_i64_zeropoison(
; CHECK-NEXT: [[TMP1:%.*]] = load i64, ptr @__msan_param_tls, align 8
; CHECK-NEXT: call void @llvm.donothing()
; CHECK-NEXT: [[_MSCZ_BS:%.*]] = icmp ne i64 [[TMP1]], 0
; CHECK-NEXT: [[_MSCZ_BZP:%.*]] = icmp eq i64 [[V:%.*]], 0
; CHECK-NEXT: [[_MSCZ_BS1:%.*]] = or i1 [[_MSCZ_BS]], [[_MSCZ_BZP]]
; CHECK-NEXT: [[_MSCZ_OS:%.*]] = sext i1 [[_MSCZ_BS1]] to i64
; CHECK-NEXT: [[TMP2:%.*]] = call i64 @llvm.cttz.i64(i64 [[V:%.*]], i1 false)
; CHECK-NEXT: [[TMP3:%.*]] = call i64 @llvm.cttz.i64(i64 [[TMP1]], i1 false)
; CHECK-NEXT: [[_MSCZ_CMP_ZEROS:%.*]] = icmp uge i64 [[TMP2]], [[TMP3]]
; CHECK-NEXT: [[_MSCZ_SHADOW_NOT_NULL:%.*]] = icmp ne i64 [[TMP1]], 0
; CHECK-NEXT: [[_MSCZ_MAIN:%.*]] = and i1 [[_MSCZ_CMP_ZEROS]], [[_MSCZ_SHADOW_NOT_NULL]]
; CHECK-NEXT: [[_MSCZ_BZP:%.*]] = icmp eq i64 [[V]], 0
; CHECK-NEXT: [[_MSCZ_BS:%.*]] = or i1 [[_MSCZ_MAIN]], [[_MSCZ_BZP]]
; CHECK-NEXT: [[_MSCZ_OS:%.*]] = sext i1 [[_MSCZ_BS]] to i64
; CHECK-NEXT: [[RES:%.*]] = call i64 @llvm.cttz.i64(i64 [[V]], i1 true)
; CHECK-NEXT: store i64 [[_MSCZ_OS]], ptr @__msan_retval_tls, align 8
; CHECK-NEXT: ret i64 [[RES]]
Expand All @@ -84,9 +104,13 @@ define i64 @test_cttz_i64_nozeropoison(i64 %v) #0 {
; CHECK-LABEL: @test_cttz_i64_nozeropoison(
; CHECK-NEXT: [[TMP1:%.*]] = load i64, ptr @__msan_param_tls, align 8
; CHECK-NEXT: call void @llvm.donothing()
; CHECK-NEXT: [[_MSCZ_BS:%.*]] = icmp ne i64 [[TMP1]], 0
; CHECK-NEXT: [[_MSCZ_OS:%.*]] = sext i1 [[_MSCZ_BS]] to i64
; CHECK-NEXT: [[RES:%.*]] = call i64 @llvm.cttz.i64(i64 [[V:%.*]], i1 false)
; CHECK-NEXT: [[TMP2:%.*]] = call i64 @llvm.cttz.i64(i64 [[V:%.*]], i1 false)
; CHECK-NEXT: [[TMP3:%.*]] = call i64 @llvm.cttz.i64(i64 [[TMP1]], i1 false)
; CHECK-NEXT: [[_MSCZ_CMP_ZEROS:%.*]] = icmp uge i64 [[TMP2]], [[TMP3]]
; CHECK-NEXT: [[_MSCZ_SHADOW_NOT_NULL:%.*]] = icmp ne i64 [[TMP1]], 0
; CHECK-NEXT: [[_MSCZ_MAIN:%.*]] = and i1 [[_MSCZ_CMP_ZEROS]], [[_MSCZ_SHADOW_NOT_NULL]]
; CHECK-NEXT: [[_MSCZ_OS:%.*]] = sext i1 [[_MSCZ_MAIN]] to i64
; CHECK-NEXT: [[RES:%.*]] = call i64 @llvm.cttz.i64(i64 [[V]], i1 false)
; CHECK-NEXT: store i64 [[_MSCZ_OS]], ptr @__msan_retval_tls, align 8
; CHECK-NEXT: ret i64 [[RES]]
;
Expand All @@ -99,10 +123,14 @@ define <2 x i64> @test_cttz_v2i64_zeropoison(<2 x i64> %v) #0 {
; CHECK-LABEL: @test_cttz_v2i64_zeropoison(
; CHECK-NEXT: [[TMP1:%.*]] = load <2 x i64>, ptr @__msan_param_tls, align 8
; CHECK-NEXT: call void @llvm.donothing()
; CHECK-NEXT: [[_MSCZ_BS:%.*]] = icmp ne <2 x i64> [[TMP1]], zeroinitializer
; CHECK-NEXT: [[_MSCZ_BZP:%.*]] = icmp eq <2 x i64> [[V:%.*]], zeroinitializer
; CHECK-NEXT: [[_MSCZ_BS1:%.*]] = or <2 x i1> [[_MSCZ_BS]], [[_MSCZ_BZP]]
; CHECK-NEXT: [[_MSCZ_OS:%.*]] = sext <2 x i1> [[_MSCZ_BS1]] to <2 x i64>
; CHECK-NEXT: [[TMP2:%.*]] = call <2 x i64> @llvm.cttz.v2i64(<2 x i64> [[V:%.*]], i1 false)
; CHECK-NEXT: [[TMP3:%.*]] = call <2 x i64> @llvm.cttz.v2i64(<2 x i64> [[TMP1]], i1 false)
; CHECK-NEXT: [[_MSCZ_CMP_ZEROS:%.*]] = icmp uge <2 x i64> [[TMP2]], [[TMP3]]
; CHECK-NEXT: [[_MSCZ_SHADOW_NOT_NULL:%.*]] = icmp ne <2 x i64> [[TMP1]], zeroinitializer
; CHECK-NEXT: [[_MSCZ_MAIN:%.*]] = and <2 x i1> [[_MSCZ_CMP_ZEROS]], [[_MSCZ_SHADOW_NOT_NULL]]
; CHECK-NEXT: [[_MSCZ_BZP:%.*]] = icmp eq <2 x i64> [[V]], zeroinitializer
; CHECK-NEXT: [[_MSCZ_BS:%.*]] = or <2 x i1> [[_MSCZ_MAIN]], [[_MSCZ_BZP]]
; CHECK-NEXT: [[_MSCZ_OS:%.*]] = sext <2 x i1> [[_MSCZ_BS]] to <2 x i64>
; CHECK-NEXT: [[RES:%.*]] = call <2 x i64> @llvm.cttz.v2i64(<2 x i64> [[V]], i1 true)
; CHECK-NEXT: store <2 x i64> [[_MSCZ_OS]], ptr @__msan_retval_tls, align 8
; CHECK-NEXT: ret <2 x i64> [[RES]]
Expand All @@ -114,9 +142,13 @@ define <2 x i64> @test_cttz_v2i64_nozeropoison(<2 x i64> %v) #0 {
; CHECK-LABEL: @test_cttz_v2i64_nozeropoison(
; CHECK-NEXT: [[TMP1:%.*]] = load <2 x i64>, ptr @__msan_param_tls, align 8
; CHECK-NEXT: call void @llvm.donothing()
; CHECK-NEXT: [[_MSCZ_BS:%.*]] = icmp ne <2 x i64> [[TMP1]], zeroinitializer
; CHECK-NEXT: [[_MSCZ_OS:%.*]] = sext <2 x i1> [[_MSCZ_BS]] to <2 x i64>
; CHECK-NEXT: [[RES:%.*]] = call <2 x i64> @llvm.cttz.v2i64(<2 x i64> [[V:%.*]], i1 false)
; CHECK-NEXT: [[TMP2:%.*]] = call <2 x i64> @llvm.cttz.v2i64(<2 x i64> [[V:%.*]], i1 false)
; CHECK-NEXT: [[TMP3:%.*]] = call <2 x i64> @llvm.cttz.v2i64(<2 x i64> [[TMP1]], i1 false)
; CHECK-NEXT: [[_MSCZ_CMP_ZEROS:%.*]] = icmp uge <2 x i64> [[TMP2]], [[TMP3]]
; CHECK-NEXT: [[_MSCZ_SHADOW_NOT_NULL:%.*]] = icmp ne <2 x i64> [[TMP1]], zeroinitializer
; CHECK-NEXT: [[_MSCZ_MAIN:%.*]] = and <2 x i1> [[_MSCZ_CMP_ZEROS]], [[_MSCZ_SHADOW_NOT_NULL]]
; CHECK-NEXT: [[_MSCZ_OS:%.*]] = sext <2 x i1> [[_MSCZ_MAIN]] to <2 x i64>
; CHECK-NEXT: [[RES:%.*]] = call <2 x i64> @llvm.cttz.v2i64(<2 x i64> [[V]], i1 false)
; CHECK-NEXT: store <2 x i64> [[_MSCZ_OS]], ptr @__msan_retval_tls, align 8
; CHECK-NEXT: ret <2 x i64> [[RES]]
;
Expand Down
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