[DirectX] Remove unused global variables #149184

kmpeng · 2025-07-16T20:52:44Z

Fixes #139023

This PR:

Removes unused global variables in the finalize linkage pass
Changes the scalar-data.ll run command to avoid removing its global variables
Adds tests to finalize_linkage.ll that make sure unused global variables are removed
Temporarily removes the llc run command from finalize_linkage.ll
- This needs to be added back once #149179 and #149180 are fixed

llvmbot · 2025-07-16T20:53:24Z

@llvm/pr-subscribers-backend-directx

Author: Kaitlin Peng (kmpeng)

Changes

Fixes #139023.

This PR:

Removes unused global variables in the finalize linkage pass
Changes the scalar-data.ll run command to avoid removing its global variables
Temporarily removes the llc run command from finalize_linkage.ll
- This needs to be added back once #149179 and #149180 are fixed

Full diff: https://github.com/llvm/llvm-project/pull/149184.diff

3 Files Affected:

(modified) llvm/lib/Target/DirectX/DXILFinalizeLinkage.cpp (+12)
(modified) llvm/test/CodeGen/DirectX/finalize_linkage.ll (+20-2)
(modified) llvm/test/CodeGen/DirectX/scalar-data.ll (+1-1)

diff --git a/llvm/lib/Target/DirectX/DXILFinalizeLinkage.cpp b/llvm/lib/Target/DirectX/DXILFinalizeLinkage.cpp
index 5f331dbd2d826..cf497d8e4bba5 100644
--- a/llvm/lib/Target/DirectX/DXILFinalizeLinkage.cpp
+++ b/llvm/lib/Target/DirectX/DXILFinalizeLinkage.cpp
@@ -28,6 +28,18 @@ static bool finalizeLinkage(Module &M) {
     }
   }
 
+  // Remove unused global variables.
+  SmallVector<GlobalVariable *> ToErase;
+  for (GlobalVariable &GV : M.globals()) {
+    if (GV.use_empty()) {
+      ToErase.push_back(&GV);
+    }
+  }
+  for (GlobalVariable *GV : ToErase) {
+    GV->eraseFromParent();
+    MadeChange = true;
+  }
+
   SmallVector<Function *> Funcs;
 
   // Collect non-entry and non-exported functions to set to internal linkage.
diff --git a/llvm/test/CodeGen/DirectX/finalize_linkage.ll b/llvm/test/CodeGen/DirectX/finalize_linkage.ll
index dc1140f1c9160..b0e9182c813f7 100644
--- a/llvm/test/CodeGen/DirectX/finalize_linkage.ll
+++ b/llvm/test/CodeGen/DirectX/finalize_linkage.ll
@@ -1,10 +1,17 @@
 ; RUN: opt -S -dxil-finalize-linkage -mtriple=dxil-unknown-shadermodel6.5-compute %s | FileCheck %s
-; RUN: llc %s --filetype=asm -o - | FileCheck %s --check-prefixes=CHECK-LLC
+; TODO: Add back the llc test once #149179 and #149180 are fixed
 
 target triple = "dxilv1.5-pc-shadermodel6.5-compute"
 
 ; DXILFinalizeLinkage changes linkage of all functions that are hidden to
-; internal, and converts private global variables to internal linkage.
+; internal, converts private global variables to internal linkage, and removes
+; unused global variables.
+
+; CHECK-NOT: @aTile
+@aTile = hidden addrspace(3) global [4 x [1 x i32]] zeroinitializer, align 4
+
+; CHECK-NOT: @bTile
+@bTile = hidden addrspace(3) global [1 x <1 x i32>] zeroinitializer, align 4
 
 ; 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
@@ -27,6 +34,17 @@ target triple = "dxilv1.5-pc-shadermodel6.5-compute"
 ; CHECK: @hidden_var = hidden global i32
 @hidden_var = hidden global i32 1, align 4
 
+define void @anchor_function() #0 {
+entry:
+  %0 = load i32, ptr @switch.table, align 4
+  %1 = load [3 x float], ptr @private_array, align 4
+  %2 = load i32, ptr @private_var, align 4
+  %3 = load i32, ptr @internal_var, align 4
+  %4 = load i32, ptr @external_var, align 4
+  %5 = load i32, ptr @hidden_var, align 4
+  ret void
+}
+
 ; CHECK-NOT: define internal void @"?f1@@YAXXZ"()
 define void @"?f1@@YAXXZ"() #0 {
 entry:
diff --git a/llvm/test/CodeGen/DirectX/scalar-data.ll b/llvm/test/CodeGen/DirectX/scalar-data.ll
index 4861a0890f136..d9c8df9bc169c 100644
--- a/llvm/test/CodeGen/DirectX/scalar-data.ll
+++ b/llvm/test/CodeGen/DirectX/scalar-data.ll
@@ -1,4 +1,4 @@
-; RUN: llc %s -mtriple=dxil-pc-shadermodel6.3-library --filetype=asm -o - | FileCheck %s
+; RUN: opt -S -passes='dxil-data-scalarization,dxil-flatten-arrays' -mtriple=dxil-unknown-shadermodel6.5-compute %s | FileCheck %s
 
 ; Make sure we don't touch arrays without vectors and that can recurse and flatten multiple-dimension arrays of vectors

farzonl · 2025-07-16T21:01:37Z

llvm/lib/Target/DirectX/DXILFinalizeLinkage.cpp

+  SmallVector<GlobalVariable *> ToErase;
+  for (GlobalVariable &GV : M.globals()) {
+    if (GV.use_empty()) {
+      ToErase.push_back(&GV);


any chance we could just do GV->eraseFromParent(); here and not need the second loop\ ToErase vector?

No, that causes it to crash. Doing GV->eraseFromParent() here removes it from the module's global list, which invalidates the iterator used in the for loop

I'm pretty sure you can get around that problem with make_early_inc_range. To be clear what I'm asking. Is it possible to do

for (GlobalVariable &GV : llvm::make_early_inc_range(M.globals())) { GV.eraseFromParent(); }

Yeah that works, I just did it this way because I was trying to follow the same format as the function removals. But I can change it

Icohedron · 2025-07-16T22:50:24Z

llvm/lib/Target/DirectX/DXILFinalizeLinkage.cpp

+  for (GlobalVariable &GV : make_early_inc_range(M.globals())) {
+    if (GV.use_empty()) {
+      GV.eraseFromParent();
+      MadeChange = true;
+    }
+  }


style nit: unecessary curly braces

Suggested change

for (GlobalVariable &GV : make_early_inc_range(M.globals())) {

if (GV.use_empty()) {

GV.eraseFromParent();

MadeChange = true;

}

}

for (GlobalVariable &GV : make_early_inc_range(M.globals()))

if (GV.use_empty()) {

GV.eraseFromParent();

MadeChange = true;

}

Icohedron · 2025-07-17T21:52:58Z

llvm/test/CodeGen/DirectX/finalize_linkage.ll

@@ -1,10 +1,17 @@
 ; RUN: opt -S -dxil-finalize-linkage -mtriple=dxil-unknown-shadermodel6.5-compute %s | FileCheck %s
-; RUN: llc %s --filetype=asm -o - | FileCheck %s --check-prefixes=CHECK-LLC
+; TODO: Add back the llc test once #149179 and #149180 are fixed


These are fixed now.

Great, thanks!

Icohedron · 2025-07-17T22:07:20Z

I recompiled all the DML shaders with this PR and it appears to completely resolve #139023.
I did not include changes from your other PR #148986 when building, so PR #148986 is not necessary to fix #139023.
However, that PR is still required for correctness.

Icohedron

The PR changes look good but you need to add the llc test since #149179 and #149180 are fixed.

Furthermore, you need to fix these dxil-dis tests which have broken with your changes:

Failed Tests (2):
  LLVM :: tools/dxil-dis/global_ctor.ll
  LLVM :: tools/dxil-dis/opaque-value_as_metadata.ll

If you have configured llvm with -DLLVM_INCLUDE_DXIL_TESTS=ON, you can run these tests by building the target check-llvm-tools-dxil-dis

kmpeng · 2025-07-17T22:31:08Z

I recompiled all the DML shaders with this PR and it appears to completely resolve #139023. I did not include changes from your other PR #148986 when building, so PR #148986 is not necessary to fix #139023. However, that PR is still required for correctness.

Yep, we realized that but didn't update it in the comments sorry. I think Farzon said he wants to redo the solution to #148986 to make it recursive, so I'll be closing that PR soon.

kmpeng · 2025-07-29T02:11:40Z

New PR that adds the GlobalDCE pass after finalize linkage instead of this approach: #151071

kmpeng marked this pull request as ready for review July 16, 2025 20:52

llvmbot added the backend:DirectX label Jul 16, 2025

farzonl reviewed Jul 16, 2025

View reviewed changes

kmpeng force-pushed the bugfix/unused-globalvars branch from 6b8ee3b to eddc1cf Compare July 16, 2025 21:28

Icohedron reviewed Jul 16, 2025

View reviewed changes

Icohedron reviewed Jul 17, 2025

View reviewed changes

Icohedron approved these changes Jul 17, 2025

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Icohedron requested changes Jul 17, 2025

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kmpeng added 2 commits July 17, 2025 15:19

remove unused global variables in finalize linkage pass

d063024

change 2 for loops to 1

0fe55a5

kmpeng force-pushed the bugfix/unused-globalvars branch from 59e6e16 to 0fe55a5 Compare July 17, 2025 22:19

Icohedron mentioned this pull request Jul 17, 2025

[DirectX] Validator is erroring with Internal declaration '.*' is unused #139023

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kmpeng closed this Jul 29, 2025

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