[llvm] 23f6c8d - [amdgpu] Always, instead of mostly, remove unused LDS symbols

[Jon Chesterfield via llvm-commits]

Author: Jon Chesterfield
Date: 2022-09-07T18:28:16+01:00
New Revision: 23f6c8d6354fa78feb5ae636205a2b1de6323c3c

URL: https://github.com/llvm/llvm-project/commit/23f6c8d6354fa78feb5ae636205a2b1de6323c3c
DIFF: https://github.com/llvm/llvm-project/commit/23f6c8d6354fa78feb5ae636205a2b1de6323c3c.diff

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

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.

Reviewed By: rampitec

Differential Revision: https://reviews.llvm.org/D133028

Added: 
    

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

Removed: 
    


################################################################################
diff  --git a/llvm/lib/Target/AMDGPU/AMDGPULowerModuleLDSPass.cpp b/llvm/lib/Target/AMDGPU/AMDGPULowerModuleLDSPass.cpp
index bc0558c52f25e..243d9ce19fd2f 100644
--- a/llvm/lib/Target/AMDGPU/AMDGPULowerModuleLDSPass.cpp
+++ b/llvm/lib/Target/AMDGPU/AMDGPULowerModuleLDSPass.cpp
@@ -244,6 +244,10 @@ class AMDGPULowerModuleLDS : public ModulePass {
       }
     }
 
+    for (auto &GV : make_early_inc_range(M.globals()))
+      if (AMDGPU::isLDSVariableToLower(GV) && GV.use_empty())
+        GV.eraseFromParent();
+    
     return Changed;
   }
 

diff  --git a/llvm/test/CodeGen/AMDGPU/lower-kernel-lds-super-align.ll b/llvm/test/CodeGen/AMDGPU/lower-kernel-lds-super-align.ll
index a6225bc7c2ed9..dfad39cb6d638 100644
--- a/llvm/test/CodeGen/AMDGPU/lower-kernel-lds-super-align.ll
+++ b/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
 

diff  --git a/llvm/test/CodeGen/AMDGPU/lower-kernel-lds.ll b/llvm/test/CodeGen/AMDGPU/lower-kernel-lds.ll
index c8592c7a52b5b..29159f18b4e12 100644
--- a/llvm/test/CodeGen/AMDGPU/lower-kernel-lds.ll
+++ b/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