[PATCH] D133028: [amdgpu] Always, instead of mostly, remove unused LDS symbols

[Jon Chesterfield via Phabricator via llvm-commits]

JonChesterfield created this revision.
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Currently LDS variables are removed by the lower module pass
if they have a use which is caught by the replace with struct control flow.
This makes tests brittle to changes to that control flow which induces
noise when trying to improve lowering. Some tests already check that
variables are removed, while others checked that they are not removed.

LDS variables are not (currently) externally accessible, and if that
changes the machinery which makes them externally accessible will look
like a use. This change therefore breaks no applications.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D133028

Files:
  llvm/lib/Target/AMDGPU/AMDGPULowerModuleLDSPass.cpp
  llvm/test/CodeGen/AMDGPU/lower-kernel-lds-super-align.ll
  llvm/test/CodeGen/AMDGPU/lower-kernel-lds.ll


Index: llvm/test/CodeGen/AMDGPU/lower-kernel-lds.ll
===================================================================
--- llvm/test/CodeGen/AMDGPU/lower-kernel-lds.ll
+++ llvm/test/CodeGen/AMDGPU/lower-kernel-lds.ll
@@ -4,14 +4,12 @@
 @lds.size.1.align.1 = internal unnamed_addr addrspace(3) global [1 x i8] undef, align 1
 @lds.size.2.align.2 = internal unnamed_addr addrspace(3) global [2 x i8] undef, align 2
 @lds.size.4.align.4 = internal unnamed_addr addrspace(3) global [4 x i8] undef, align 4
- at lds.size.8.align.8 = internal unnamed_addr addrspace(3) global [8 x i8] undef, align 8
 @lds.size.16.align.16 = internal unnamed_addr addrspace(3) global [16 x i8] undef, align 16
 
 ; CHECK: %llvm.amdgcn.kernel.k0.lds.t = type { [16 x i8], [4 x i8], [2 x i8], [1 x i8] }
 ; CHECK: %llvm.amdgcn.kernel.k1.lds.t = type { [16 x i8], [4 x i8], [2 x i8] }
 
 ;.
-; CHECK: @lds.size.8.align.8 = internal unnamed_addr addrspace(3) global [8 x i8] undef, align 8
 ; CHECK: @lds.k2 = addrspace(3) global [1 x i8] undef, align 1
 ; CHECK: @llvm.amdgcn.kernel.k0.lds = internal addrspace(3) global %llvm.amdgcn.kernel.k0.lds.t undef, align 16
 ; CHECK: @llvm.amdgcn.kernel.k1.lds = internal addrspace(3) global %llvm.amdgcn.kernel.k1.lds.t undef, align 16
Index: llvm/test/CodeGen/AMDGPU/lower-kernel-lds-super-align.ll
===================================================================
--- llvm/test/CodeGen/AMDGPU/lower-kernel-lds-super-align.ll
+++ llvm/test/CodeGen/AMDGPU/lower-kernel-lds-super-align.ll
@@ -12,6 +12,8 @@
 ; SUPER-ALIGN_OFF: @lds.unused = addrspace(3) global i32 undef, align 2
 @lds.unused = addrspace(3) global i32 undef, align 2
 
+ at llvm.used = appending global [1 x i8*] [i8* addrspacecast (i32 addrspace(3)* @lds.unused to i8*)], section "llvm.metadata"
+
 ; CHECK-NOT: @lds.1
 @lds.1 = internal unnamed_addr addrspace(3) global [32 x i8] undef, align 1
 
Index: llvm/lib/Target/AMDGPU/AMDGPULowerModuleLDSPass.cpp
===================================================================
--- llvm/lib/Target/AMDGPU/AMDGPULowerModuleLDSPass.cpp
+++ llvm/lib/Target/AMDGPU/AMDGPULowerModuleLDSPass.cpp
@@ -245,6 +245,14 @@
       }
     }
 
+    for (auto &GV : make_early_inc_range(M.globals())) {
+      if (AMDGPU::isLDSVariableToLower(GV)) {
+        if (GV.use_empty()) {
+          GV.eraseFromParent();
+        }
+      }
+    }
+    
     return Changed;
   }
 


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