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Translate OpUndef to poison instead of undef in SPIR-V reader #3661

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Translate OpUndef to poison instead of undef in SPIR-V reader #3661

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2 changes: 1 addition & 1 deletion lib/SPIRV/SPIRVReader.cpp
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Expand Up @@ -1704,7 +1704,7 @@ Value *SPIRVToLLVM::transValueWithoutDecoration(SPIRVValue *BV, Function *F,
}

case OpUndef:
return mapValue(BV, UndefValue::get(transType(BV->getType())));
return mapValue(BV, PoisonValue::get(transType(BV->getType())));
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@MrSidims MrSidims Mar 18, 2026

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We can't do the replacement unconditionally. If we really want to invest into this, then we should do this following https://registry.khronos.org/SPIR-V/specs/unified1/SPIRV.html#_validity_and_defined_behavior aka check which instruction generates/consume OpUndef and if consuming this undef/poison value is forbidden for an instruction - undef should be generated in LLVM IR, and poison otherwise.

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@aobolensk aobolensk Mar 18, 2026

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Fair enough. Shall we follow the logic described in the spec directly? As I can see, there could be several "forbidden consumers" such as conditional branch instructions. Or are there any other assumptions? The check seems to be very non-elegant, because it tries to evaluate the context of the users (other mappers here do not perform such checks)

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@MrSidims MrSidims Mar 20, 2026 •
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Please correct me if I'm wrong. The patch addresses this fixme, right? If so, I would like to understand, why roundtrip through llvm-spirv alone and through backend + llvm-spirv are different before suggesting an approach.


case OpSizeOf: {
Type *ResTy = transType(BV->getType());
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2 changes: 1 addition & 1 deletion test/DebugInfo/DebugInfoLLVMArg.ll
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Expand Up @@ -65,7 +65,7 @@ entry:
; CHECK-LLVM-OCL: #dbg_value(!DIArgList(ptr %x), ![[#]], !DIExpression(DW_OP_LLVM_arg, 0), ![[#]])
; CHECK-LLVM-200: #dbg_value(!DIArgList(ptr %x), ![[#]], !DIExpression(DW_OP_LLVM_arg, 0), ![[#]])
call void @llvm.dbg.value(metadata !DIArgList(ptr %x), metadata !6, metadata !DIExpression(DW_OP_LLVM_arg, 0)), !dbg !10
; CHECK-LLVM-OCL: #dbg_value(ptr undef, ![[#]], !DIExpression(), ![[#]])
; CHECK-LLVM-OCL: #dbg_value(ptr poison, ![[#]], !DIExpression(), ![[#]])
; CHECK-LLVM-200: #dbg_value(!DIArgList(ptr %x, ptr %x), ![[#]], !DIExpression(DW_OP_LLVM_arg, 0, DW_OP_LLVM_arg, 1, DW_OP_plus)
call void @llvm.dbg.value(metadata !DIArgList(ptr %x, ptr %x), metadata !6, metadata !DIExpression(DW_OP_LLVM_arg, 0, DW_OP_LLVM_arg, 1, DW_OP_plus)), !dbg !10
store i32 42, ptr %x, align 4
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2 changes: 1 addition & 1 deletion test/complex-constexpr-vector.ll
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Expand Up @@ -56,7 +56,7 @@ entry:
; CHECK-LLVM-SAME: i8 add (
; CHECK-LLVM-SAME: i8 extractelement (<8 x i8> bitcast (<2 x i32> splat (i32 65793) to <8 x i8>), i32 2),
; CHECK-LLVM-SAME: i8 extractelement (<8 x i8> bitcast (<2 x i32> splat (i32 131586) to <8 x i8>), i32 2)),
; CHECK-LLVM-SAME: i8 undef>,
; CHECK-LLVM-SAME: i8 poison>,
; CHECK-LLVM-SAME: ![[#]], !DIExpression(), ![[#]])

; CHECK-LLC: target triple = "spir64-unknown-unknown"
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4 changes: 2 additions & 2 deletions test/freeze.ll
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Expand Up @@ -125,7 +125,7 @@ define spir_func i64 @testfunction_ptrB(ptr addrspace(1) %val) {
}

; CHECK-LLC: @testfunction_ptrB
; CHECK-LLC-NEXT: ptrtoint ptr undef to i64
; CHECK-LLC-NEXT: ptrtoint ptr poison to i64

; CHECK-LLVM: @testfunction_ptrC
; Frozen poison/undef should produce a constant.
Expand All @@ -138,4 +138,4 @@ define spir_func i64 @testfunction_ptrC(ptr addrspace(1) %val) {
}

; CHECK-LLC: @testfunction_ptrC
; CHECK-LLC-NEXT: ptrtoint ptr undef to i64
; CHECK-LLC-NEXT: ptrtoint ptr poison to i64
2 changes: 1 addition & 1 deletion test/global-var-name-linkage.ll
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Expand Up @@ -45,7 +45,7 @@ target triple = "spir64-unknown-unknown"
; CHECK-DAG: Decorate [[#id38]] Constant
; CHECK-DAG: Decorate [[#id38]] Alignment 4

; CHECK-LLVM: @G1 = internal addrspace(1) constant %"class.sycl::_V1::nd_item" undef, align 1
; CHECK-LLVM: @G1 = internal addrspace(1) constant %"class.sycl::_V1::nd_item" poison, align 1
; CHECK-LLVM: @g1 = addrspace(1) global i32 1, align 4
; CHECK-LLVM: @g2 = internal addrspace(1) global i32 2, align 4
; CHECK-LLVM: @g4 = common addrspace(1) global i32 0, align 4
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4 changes: 2 additions & 2 deletions test/llvm-intrinsics/frexp.ll
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Expand Up @@ -80,7 +80,7 @@ define { float, i32 } @frexp_negzero() {
}

; CHECK-SPIRV: ExtInst [[#TypeDouble]] [[#]] [[#ExtInstSetId]] frexp [[#UndefDouble]] [[#]]
; CHECK-LLVM: call spir_func double @_Z5frexpdPi(double undef, ptr %[[#]])
; CHECK-LLVM: call spir_func double @_Z5frexpdPi(double poison, ptr %[[#]])
; CHECK-LLVM: ret %[[StrTypeDoubleInt]]
define { double, i32 } @frexp_undef() {
%ret = call { double, i32 } @llvm.frexp.f64.i32(double undef)
Expand All @@ -104,7 +104,7 @@ define { <2 x float>, <2 x i32> } @frexp_zero_negzero_vector() {
}

; CHECK-SPIRV: ExtInst [[#VecFloat4]] [[#]] [[#ExtInstSetId]] frexp [[#]] [[#]]
; CHECK-LLVM: call spir_func <4 x float> @_Z5frexpDv4_fPDv4_i(<4 x float> <float 1.600000e+01, float -3.200000e+01, float undef, float 9.999000e+03>, ptr %[[#]])
; CHECK-LLVM: call spir_func <4 x float> @_Z5frexpDv4_fPDv4_i(<4 x float> <float 1.600000e+01, float -3.200000e+01, float poison, float 9.999000e+03>, ptr %[[#]])
; CHECK-LLVM: ret %[[StrTypeFloatIntVec4]]
define { <4 x float>, <4 x i32> } @frexp_nonsplat_vector() {
%ret = call { <4 x float>, <4 x i32> } @llvm.frexp.v4f32.v4i32(<4 x float> <float 16.0, float -32.0, float undef, float 9999.0>)
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8 changes: 4 additions & 4 deletions test/llvm-intrinsics/uadd.with.overflow.ll
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Expand Up @@ -84,7 +84,7 @@ entry:
; CHECK-LLVM: %8 = extractvalue [[structtype]] %7, 0
; CHECK-LLVM: %9 = extractvalue [[structtype]] %7, 1
; CHECK-LLVM: %10 = icmp ne i16 %9, 0
; CHECK-LLVM: %11 = insertvalue [[structtype_0]] undef, i16 %8, 0
; CHECK-LLVM: %11 = insertvalue [[structtype_0]] poison, i16 %8, 0
; CHECK-LLVM: %12 = insertvalue [[structtype_0]] %11, i1 %10, 1
; CHECK-LLVM: %13 = extractvalue [[structtype_0]] %12, 0
; CHECK-LLVM: %14 = extractvalue [[structtype_0]] %12, 1
Expand Down Expand Up @@ -126,7 +126,7 @@ entry:
; CHECK-LLVM: %8 = extractvalue [[structtype_1]] %7, 0
; CHECK-LLVM: %9 = extractvalue [[structtype_1]] %7, 1
; CHECK-LLVM: %10 = icmp ne i32 %9, 0
; CHECK-LLVM: %11 = insertvalue [[structtype_2]] undef, i32 %8, 0
; CHECK-LLVM: %11 = insertvalue [[structtype_2]] poison, i32 %8, 0
; CHECK-LLVM: %12 = insertvalue [[structtype_2]] %11, i1 %10, 1
; CHECK-LLVM: %13 = extractvalue [[structtype_2]] %12, 0
; CHECK-LLVM: %14 = extractvalue [[structtype_2]] %12, 1
Expand Down Expand Up @@ -167,7 +167,7 @@ entry:
; CHECK-LLVM: %8 = extractvalue [[structtype_3]] %7, 0
; CHECK-LLVM: %9 = extractvalue [[structtype_3]] %7, 1
; CHECK-LLVM: %10 = icmp ne i64 %9, 0
; CHECK-LLVM: %11 = insertvalue [[structtype_4]] undef, i64 %8, 0
; CHECK-LLVM: %11 = insertvalue [[structtype_4]] poison, i64 %8, 0
; CHECK-LLVM: %12 = insertvalue [[structtype_4]] %11, i1 %10, 1
; CHECK-LLVM: %13 = extractvalue [[structtype_4]] %12, 0
; CHECK-LLVM: %14 = extractvalue [[structtype_4]] %12, 1
Expand Down Expand Up @@ -208,7 +208,7 @@ entry:
; CHECK-LLVM: %8 = extractvalue [[structtype_5]] %7, 0
; CHECK-LLVM: %9 = extractvalue [[structtype_5]] %7, 1
; CHECK-LLVM: %10 = icmp ne <4 x i32> %9, zeroinitializer
; CHECK-LLVM: %11 = insertvalue [[structtype_6]] undef, <4 x i32> %8, 0
; CHECK-LLVM: %11 = insertvalue [[structtype_6]] poison, <4 x i32> %8, 0
; CHECK-LLVM: %12 = insertvalue [[structtype_6]] %11, <4 x i1> %10, 1
; CHECK-LLVM: %13 = extractvalue [[structtype_6]] %12, 0
; CHECK-LLVM: %14 = extractvalue [[structtype_6]] %12, 1
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8 changes: 4 additions & 4 deletions test/llvm-intrinsics/usub.with.overflow.ll
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Expand Up @@ -84,7 +84,7 @@ entry:
; CHECK-LLVM: %8 = extractvalue [[structtype]] %7, 0
; CHECK-LLVM: %9 = extractvalue [[structtype]] %7, 1
; CHECK-LLVM: %10 = icmp ne i16 %9, 0
; CHECK-LLVM: %11 = insertvalue [[structtype_0]] undef, i16 %8, 0
; CHECK-LLVM: %11 = insertvalue [[structtype_0]] poison, i16 %8, 0
; CHECK-LLVM: %12 = insertvalue [[structtype_0]] %11, i1 %10, 1
; CHECK-LLVM: %13 = extractvalue [[structtype_0]] %12, 0
; CHECK-LLVM: %14 = extractvalue [[structtype_0]] %12, 1
Expand Down Expand Up @@ -126,7 +126,7 @@ entry:
; CHECK-LLVM: %8 = extractvalue [[structtype_1]] %7, 0
; CHECK-LLVM: %9 = extractvalue [[structtype_1]] %7, 1
; CHECK-LLVM: %10 = icmp ne i32 %9, 0
; CHECK-LLVM: %11 = insertvalue [[structtype_2]] undef, i32 %8, 0
; CHECK-LLVM: %11 = insertvalue [[structtype_2]] poison, i32 %8, 0
; CHECK-LLVM: %12 = insertvalue [[structtype_2]] %11, i1 %10, 1
; CHECK-LLVM: %13 = extractvalue [[structtype_2]] %12, 0
; CHECK-LLVM: %14 = extractvalue [[structtype_2]] %12, 1
Expand Down Expand Up @@ -167,7 +167,7 @@ entry:
; CHECK-LLVM: %8 = extractvalue [[structtype_3]] %7, 0
; CHECK-LLVM: %9 = extractvalue [[structtype_3]] %7, 1
; CHECK-LLVM: %10 = icmp ne i64 %9, 0
; CHECK-LLVM: %11 = insertvalue [[structtype_4]] undef, i64 %8, 0
; CHECK-LLVM: %11 = insertvalue [[structtype_4]] poison, i64 %8, 0
; CHECK-LLVM: %12 = insertvalue [[structtype_4]] %11, i1 %10, 1
; CHECK-LLVM: %13 = extractvalue [[structtype_4]] %12, 0
; CHECK-LLVM: %14 = extractvalue [[structtype_4]] %12, 1
Expand Down Expand Up @@ -208,7 +208,7 @@ entry:
; CHECK-LLVM: %8 = extractvalue [[structtype_5]] %7, 0
; CHECK-LLVM: %9 = extractvalue [[structtype_5]] %7, 1
; CHECK-LLVM: %10 = icmp ne <4 x i32> %9, zeroinitializer
; CHECK-LLVM: %11 = insertvalue [[structtype_6]] undef, <4 x i32> %8, 0
; CHECK-LLVM: %11 = insertvalue [[structtype_6]] poison, <4 x i32> %8, 0
; CHECK-LLVM: %12 = insertvalue [[structtype_6]] %11, <4 x i1> %10, 1
; CHECK-LLVM: %13 = extractvalue [[structtype_6]] %12, 0
; CHECK-LLVM: %14 = extractvalue [[structtype_6]] %12, 1
Expand Down
4 changes: 2 additions & 2 deletions test/opundef.spt
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Expand Up @@ -45,10 +45,10 @@

; CHECK: define spir_func %structtype @foo() #0 {
; CHECK-NEXT: entry:
; CHECK-NEXT: ret %structtype { i32 1, float undef }
; CHECK-NEXT: ret %structtype { i32 1, float poison }
; CHECK-NEXT: }
; CHECK: define spir_func %structtype @bar() #0 {
; CHECK-NEXT: entry:
; CHECK-NEXT: ret %structtype { i32 1, float undef }
; CHECK-NEXT: ret %structtype { i32 1, float poison }
; CHECK-NEXT: }

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