[clang] [AMDGPU] fix amdgpu_max_num_work_groups in templates (PR #141633)

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llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-backend-amdgpu

Author: Yaxun (Sam) Liu (yxsamliu)

<details>
<summary>Changes</summary>

Clang does not instantiate amdgpu_max_num_work_groups attribute with one template argument, causing
assertion codegen.

Fixes: https://github.com/llvm/llvm-project/issues/139570

---
Full diff: https://github.com/llvm/llvm-project/pull/141633.diff


2 Files Affected:

- (modified) clang/lib/Sema/SemaTemplateInstantiateDecl.cpp (+22-13) 
- (modified) clang/test/CodeGenCUDA/amdgpu-kernel-attrs.cu (+6) 


``````````diff
diff --git a/clang/lib/Sema/SemaTemplateInstantiateDecl.cpp b/clang/lib/Sema/SemaTemplateInstantiateDecl.cpp
index 44700a446dfac..174c8fc59e4fa 100644
--- a/clang/lib/Sema/SemaTemplateInstantiateDecl.cpp
+++ b/clang/lib/Sema/SemaTemplateInstantiateDecl.cpp
@@ -648,21 +648,30 @@ static void instantiateDependentAMDGPUMaxNumWorkGroupsAttr(
   EnterExpressionEvaluationContext Unevaluated(
       S, Sema::ExpressionEvaluationContext::ConstantEvaluated);
 
-  ExprResult ResultX = S.SubstExpr(Attr.getMaxNumWorkGroupsX(), TemplateArgs);
-  if (!ResultX.isUsable())
-    return;
-  ExprResult ResultY = S.SubstExpr(Attr.getMaxNumWorkGroupsY(), TemplateArgs);
-  if (!ResultY.isUsable())
-    return;
-  ExprResult ResultZ = S.SubstExpr(Attr.getMaxNumWorkGroupsZ(), TemplateArgs);
-  if (!ResultZ.isUsable())
-    return;
+  Expr *XExpr = nullptr;
+  Expr *YExpr = nullptr;
+  Expr *ZExpr = nullptr;
+
+  if (Attr.getMaxNumWorkGroupsX()) {
+    ExprResult ResultX = S.SubstExpr(Attr.getMaxNumWorkGroupsX(), TemplateArgs);
+    if (ResultX.isUsable())
+      XExpr = ResultX.getAs<Expr>();
+  }
+
+  if (Attr.getMaxNumWorkGroupsY()) {
+    ExprResult ResultY = S.SubstExpr(Attr.getMaxNumWorkGroupsY(), TemplateArgs);
+    if (ResultY.isUsable())
+      YExpr = ResultY.getAs<Expr>();
+  }
 
-  Expr *XExpr = ResultX.getAs<Expr>();
-  Expr *YExpr = ResultY.getAs<Expr>();
-  Expr *ZExpr = ResultZ.getAs<Expr>();
+  if (Attr.getMaxNumWorkGroupsZ()) {
+    ExprResult ResultZ = S.SubstExpr(Attr.getMaxNumWorkGroupsZ(), TemplateArgs);
+    if (ResultZ.isUsable())
+      ZExpr = ResultZ.getAs<Expr>();
+  }
 
-  S.AMDGPU().addAMDGPUMaxNumWorkGroupsAttr(New, Attr, XExpr, YExpr, ZExpr);
+  if (XExpr)
+    S.AMDGPU().addAMDGPUMaxNumWorkGroupsAttr(New, Attr, XExpr, YExpr, ZExpr);
 }
 
 // This doesn't take any template parameters, but we have a custom action that
diff --git a/clang/test/CodeGenCUDA/amdgpu-kernel-attrs.cu b/clang/test/CodeGenCUDA/amdgpu-kernel-attrs.cu
index 253ac0898f546..ced0059e69d9b 100644
--- a/clang/test/CodeGenCUDA/amdgpu-kernel-attrs.cu
+++ b/clang/test/CodeGenCUDA/amdgpu-kernel-attrs.cu
@@ -78,6 +78,12 @@ __global__ void template_32_4_a_max_num_work_groups() {}
 template __global__ void template_32_4_a_max_num_work_groups<2>();
 // CHECK: define{{.*}} amdgpu_kernel void @_Z35template_32_4_a_max_num_work_groupsILj2EEvv() [[MAX_NUM_WORK_GROUPS_32_4_2:#[0-9]+]]
 
+template<unsigned a>
+__attribute__((amdgpu_max_num_work_groups(a)))
+__global__ void template_a_max_num_work_groups() {}
+template __global__ void template_a_max_num_work_groups<32>();
+// CHECK: define{{.*}} amdgpu_kernel void @_Z30template_a_max_num_work_groupsILj32EEvv() [[MAX_NUM_WORK_GROUPS_32_1_1]]
+
 // Make sure this is silently accepted on other targets.
 // NAMD-NOT: "amdgpu-flat-work-group-size"
 // NAMD-NOT: "amdgpu-waves-per-eu"

``````````

</details>


https://github.com/llvm/llvm-project/pull/141633