[llvm] [AMDGPU][PromoteAlloca] Support memsets to ptr allocas (PR #80678)

[via llvm-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-backend-amdgpu

Author: Pierre van Houtryve (Pierre-vh)

<details>
<summary>Changes</summary>

Fixes #<!-- -->80366

---
Full diff: https://github.com/llvm/llvm-project/pull/80678.diff


2 Files Affected:

- (modified) llvm/lib/Target/AMDGPU/AMDGPUPromoteAlloca.cpp (+12-4) 
- (modified) llvm/test/CodeGen/AMDGPU/promote-alloca-memset.ll (+12) 


``````````diff
diff --git a/llvm/lib/Target/AMDGPU/AMDGPUPromoteAlloca.cpp b/llvm/lib/Target/AMDGPU/AMDGPUPromoteAlloca.cpp
index 5e73411cae9b70..c1b244f50d93f8 100644
--- a/llvm/lib/Target/AMDGPU/AMDGPUPromoteAlloca.cpp
+++ b/llvm/lib/Target/AMDGPU/AMDGPUPromoteAlloca.cpp
@@ -521,10 +521,18 @@ static Value *promoteAllocaUserToVector(
       // For memset, we don't need to know the previous value because we
       // currently only allow memsets that cover the whole alloca.
       Value *Elt = MSI->getOperand(1);
-      if (DL.getTypeStoreSize(VecEltTy) > 1) {
-        Value *EltBytes =
-            Builder.CreateVectorSplat(DL.getTypeStoreSize(VecEltTy), Elt);
-        Elt = Builder.CreateBitCast(EltBytes, VecEltTy);
+      const unsigned BytesPerElt = DL.getTypeStoreSize(VecEltTy);
+      if (BytesPerElt > 1) {
+        Value *EltBytes = Builder.CreateVectorSplat(BytesPerElt, Elt);
+
+        // If the element type of the vector is a pointer, we need to first cast
+        // to an integer, then use a PtrCast.
+        if (VecEltTy->isPointerTy()) {
+          Type *PtrInt = Builder.getIntNTy(BytesPerElt * 8);
+          Elt = Builder.CreateBitCast(EltBytes, PtrInt);
+          Elt = Builder.CreateIntToPtr(Elt, VecEltTy);
+        } else
+          Elt = Builder.CreateBitCast(EltBytes, VecEltTy);
       }
 
       return Builder.CreateVectorSplat(VectorTy->getElementCount(), Elt);
diff --git a/llvm/test/CodeGen/AMDGPU/promote-alloca-memset.ll b/llvm/test/CodeGen/AMDGPU/promote-alloca-memset.ll
index 15af1f17e230ec..829e7a1b84e90c 100644
--- a/llvm/test/CodeGen/AMDGPU/promote-alloca-memset.ll
+++ b/llvm/test/CodeGen/AMDGPU/promote-alloca-memset.ll
@@ -84,4 +84,16 @@ entry:
   ret void
 }
 
+define amdgpu_kernel void @memset_ptr_alloca(ptr %out) {
+; CHECK-LABEL: @memset_ptr_alloca(
+; CHECK-NEXT:    store i64 0, ptr [[OUT:%.*]], align 8
+; CHECK-NEXT:    ret void
+;
+  %alloca = alloca [6 x ptr], align 16, addrspace(5)
+  call void @llvm.memset.p5.i64(ptr addrspace(5) %alloca, i8 0, i64 48, i1 false)
+  %load = load i64, ptr addrspace(5) %alloca
+  store i64 %load, ptr %out
+  ret void
+}
+
 declare void @llvm.memset.p5.i64(ptr addrspace(5) nocapture writeonly, i8, i64, i1 immarg)

``````````

</details>


https://github.com/llvm/llvm-project/pull/80678