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Drop undef/poison initializers for global variables in SPIR-V translation #3661

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Drop undef/poison initializers for global variables in SPIR-V translation #3661

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20 changes: 14 additions & 6 deletions lib/SPIRV/SPIRVWriter.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -2073,12 +2073,20 @@ LLVMToSPIRVBase::transValueWithoutDecoration(Value *V, SPIRVBasicBlock *BB,

if (auto *GV = dyn_cast<GlobalVariable>(V)) {
llvm::Type *Ty = Scavenger->getScavengedType(GV);
// Though variables with common linkage type are initialized by 0,
// they can be represented in SPIR-V as uninitialized variables with
// 'Export' linkage type, just as tentative definitions look in C
llvm::Constant *Init = GV->hasInitializer() && !GV->hasCommonLinkage()
? GV->getInitializer()
: nullptr;
// Check whether the global has an initializer for SPIR-V.
// Variables with common linkage are represented as uninitialized with
// 'Export' linkage, just as tentative definitions look in C.
// Undef/poison initializers are dropped unless the variable is constant
// with an aggregate type
auto HasInit = [](const GlobalVariable *GV) {
if (!GV->hasInitializer() || GV->hasCommonLinkage())
return false;
if (isa<UndefValue>(GV->getInitializer()))
return GV->isConstant() &&
GV->getInitializer()->getType()->isAggregateType();
return true;
};
llvm::Constant *Init = HasInit(GV) ? GV->getInitializer() : nullptr;
SPIRVValue *BVarInit = nullptr;
StructType *ST = Init ? dyn_cast<StructType>(Init->getType()) : nullptr;
if (ST && ST->hasName() && isSPIRVConstantName(ST->getName())) {
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12 changes: 6 additions & 6 deletions test/var_undef.ll
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Expand Up @@ -7,17 +7,17 @@
; RUN: llvm-spirv -r %t.spv -o %t.rev.bc
; RUN: llvm-dis %t.rev.bc -o %t.rev.ll
; RUN: FileCheck < %t.rev.ll %s --check-prefix CHECK-LLVM
; FIXME: FILECHECK_FAIL during llvm-spirv -r in llc compilation flow
; RUN: %if spirv-backend %{ llc -O0 -mtriple=spirv64-unknown-unknown -filetype=obj %s -o %t.llc.spv %}
; RUN: %if spirv-backend %{ llvm-spirv -r %t.llc.spv -o %t.llc.rev.bc %}
; RUN: %if spirv-backend %{ llvm-dis %t.llc.rev.bc -o %t.llc.rev.ll %}
; RUN: %if spirv-backend %{ FileCheck %s --input-file %t.llc.rev.ll --check-prefix CHECK-LLVM %}

; CHECK-SPIRV: Name [[FOO_VAR:[0-9]+]] "foo"
; CHECK-SPIRV: Name [[BAR_VAR:[0-9]+]] "bar"
;; foo variable has optional initializer (OpUndef)
; CHECK-SPIRV: 5 Variable [[#]] [[FOO_VAR]]
;; bar variable does not have optional initializer
;; word count must be 4
; CHECK-SPIRV: 4 Variable [[#]] [[FOO_VAR]]
; CHECK-SPIRV: 4 Variable [[#]] [[BAR_VAR]]

; CHECK-LLVM: @foo = internal addrspace(3) global %anon undef, align 8
; CHECK-LLVM: @foo = internal addrspace(3) global %anon poison, align 8
; CHECK-LLVM: @bar = internal addrspace(3) global %range poison, align 8

target datalayout = "e-i64:64-v16:16-v24:32-v32:32-v48:64-v96:128-v192:256-v256:256-v512:512-v1024:1024-n8:16:32:64"
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