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[DirectX] Convert private global variables to internal linkage during Finalize Linkage pass #146406

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Merged
merged 2 commits into from
Jul 7, 2025
Merged

[DirectX] Convert private global variables to internal linkage during Finalize Linkage pass #146406

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6a3aedc
fix switch.table.* bug - convert private global variables to internal…
kmpeng Jun 30, 2025
52b874b
add tests
kmpeng Jul 2, 2025
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20 changes: 17 additions & 3 deletions llvm/lib/Target/DirectX/DXILFinalizeLinkage.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -18,6 +18,16 @@
using namespace llvm;

static bool finalizeLinkage(Module &M) {
bool MadeChange = false;

// Convert private global variables to internal linkage.
for (GlobalVariable &GV : M.globals()) {
if (GV.hasPrivateLinkage()) {
GV.setLinkage(GlobalValue::InternalLinkage);
MadeChange = true;
}
Comment on lines +25 to +28
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Should we be removing these if GV.use_empty() to match what we do with functions? Alternatively, if we don't expect to ever get here with unused private globals, can we assert(!GV.use_empty()) here? Or is it okay/expected for us to leave unused internal variables around?

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Thats the solution we worked for this ticket #139023. My understanding was though we didn't want to blanket do this because of external linkage. so, I suppose we could do something like

if(GV.use_empty() && !GV.hasExtenalLinkage())
    ToErase.push_back(&G);

}

SmallVector<Function *> Funcs;

// Collect non-entry and non-exported functions to set to internal linkage.
Expand All @@ -32,13 +42,17 @@ static bool finalizeLinkage(Module &M) {
}

for (Function *F : Funcs) {
if (F->getLinkage() == GlobalValue::ExternalLinkage)
if (F->getLinkage() == GlobalValue::ExternalLinkage) {
F->setLinkage(GlobalValue::InternalLinkage);
if (F->isDefTriviallyDead())
MadeChange = true;
}
if (F->isDefTriviallyDead()) {
M.getFunctionList().erase(F);
MadeChange = true;
}
}

return false;
return MadeChange;
}

PreservedAnalyses DXILFinalizeLinkage::run(Module &M,
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23 changes: 22 additions & 1 deletion llvm/test/CodeGen/DirectX/finalize_linkage.ll
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Original file line number Diff line number Diff line change
Expand Up @@ -4,7 +4,28 @@
target triple = "dxilv1.5-pc-shadermodel6.5-compute"

; DXILFinalizeLinkage changes linkage of all functions that are hidden to
; internal.
; internal, and converts private global variables to internal linkage.

; CHECK: @switch.table = internal unnamed_addr constant [4 x i32]
@switch.table = private unnamed_addr constant [4 x i32] [i32 1, i32 257, i32 65793, i32 16843009], align 4

; CHECK: @private_array = internal constant [3 x float]
@private_array = private constant [3 x float] [float 1.0, float 2.0, float 3.0], align 4

; CHECK: @private_var = internal global i32
@private_var = private global i32 1, align 4

; Internal global should remain internal
; CHECK: @internal_var = internal global i32
@internal_var = internal global i32 1, align 4

; External global should remain external
; CHECK: @external_var = external global i32
@external_var = external global i32, align 4

; Hidden global should remain hidden
; CHECK: @hidden_var = hidden global i32
@hidden_var = hidden global i32 1, align 4

; CHECK-NOT: define internal void @"?f1@@YAXXZ"()
define void @"?f1@@YAXXZ"() #0 {
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