[AMDGPU] Fix module split's assumption on kernels

Module split assumes that a kernel function must have an external
linkage; however, that isn't the case.  For example, a static kernel
function will have a weak_odr linkage

Change-Id: I1e5dee0de1fd866b365f4090a574e1b2961f8dca

Author: scchan

llvm/lib/Target/AMDGPU/AMDGPUSplitModule.cpp

@@ -157,13 +157,12 @@ static auto formatRatioOf(CostType Num, CostType Dem) {
 /// Non-copyable functions cannot be cloned into multiple partitions, and only
 /// one copy of the function can be present across all partitions.
 ///
-/// External functions fall into this category. If we were to clone them, we
-/// would end up with multiple symbol definitions and a very unhappy linker.
+/// Kernel functions and external functions fall into this category. If we were 
+/// to clone them, we would end up with multiple symbol definitions and a very 
+/// unhappy linker.
 static bool isNonCopyable(const Function &F) {
-  assert(AMDGPU::isEntryFunctionCC(F.getCallingConv())
-             ? F.hasExternalLinkage()
-             : true && "Kernel w/o external linkage?");
-  return F.hasExternalLinkage() || !F.isDefinitionExact();
+  return AMDGPU::isEntryFunctionCC(F.getCallingConv()) ||
+         F.hasExternalLinkage() || !F.isDefinitionExact();
 }
 
 /// If \p GV has local linkage, make it external + hidden.

llvm/test/tools/llvm-split/AMDGPU/large-kernels-merging.ll

@@ -19,7 +19,7 @@
 ; CHECK0: declare
 
 ; CHECK1: define internal void @HelperC()
-; CHECK1: define amdgpu_kernel void @C
+; CHECK1: define weak_odr amdgpu_kernel void @C
 
 ; CHECK2: define internal void @large2()
 ; CHECK2: define internal void @large1()
@@ -30,7 +30,7 @@
 ; CHECK2: define amdgpu_kernel void @B
 
 ; NOLARGEKERNELS-CHECK0: define internal void @HelperC()
-; NOLARGEKERNELS-CHECK0: define amdgpu_kernel void @C
+; NOLARGEKERNELS-CHECK0: define weak_odr amdgpu_kernel void @C
 
 ; NOLARGEKERNELS-CHECK1: define internal void @large2()
 ; NOLARGEKERNELS-CHECK1: define internal void @large1()
@@ -88,7 +88,7 @@ define internal void @HelperC() {
   ret void
 }
 
-define amdgpu_kernel void @C() {
+define weak_odr amdgpu_kernel void @C() {
   call void @HelperC()
   ret void
 }