[ThinLTO] Don't convert functions to declarations if force-import-all is enabled

On one hand, we intend to `force-import-all` functions when the option is
enabled. On the other hand, we currently drop definitions of some functions and
convert them to declarations, which contradicts this intent.

With this PR, functions will no longer be converted to declarations when
`force-import-all` is enabled.

Author: shiltian

llvm/lib/Transforms/IPO/FunctionImport.cpp

@@ -1701,13 +1701,16 @@ void llvm::thinLTOFinalizeInModule(Module &TheModule,
     if (NewLinkage == GV.getLinkage())
       return;
 
+    bool ForceImportFunction = isa<Function>(GV) && ForceImportAll;
+
     // Check for a non-prevailing def that has interposable linkage
     // (e.g. non-odr weak or linkonce). In that case we can't simply
     // convert to available_externally, since it would lose the
     // interposable property and possibly get inlined. Simply drop
     // the definition in that case.
     if (GlobalValue::isAvailableExternallyLinkage(NewLinkage) &&
-        GlobalValue::isInterposableLinkage(GV.getLinkage())) {
+        GlobalValue::isInterposableLinkage(GV.getLinkage()) &&
+        !ForceImportFunction) {
       if (!convertToDeclaration(GV))
         // FIXME: Change this to collect replaced GVs and later erase
         // them from the parent module once thinLTOResolvePrevailingGUID is

llvm/test/ThinLTO/AMDGPU/Inputs/noinline.ll

@@ -0,0 +1,15 @@
+define void @f2(ptr %v) #0 {
+entry:
+  %v.addr = alloca ptr, align 8, addrspace(5)
+  store ptr %v, ptr addrspace(5) %v.addr, align 8
+  call void @f3(ptr %v)
+  ret void
+}
+
+define weak hidden void @f3(ptr %v) #0 {
+entry:
+  store i32 12345, ptr %v
+  ret void
+}
+
+attributes #0 = { noinline }

llvm/test/ThinLTO/AMDGPU/force-import-all.ll

@@ -0,0 +1,27 @@
+; RUN: opt -mtriple=amdgcn-amd-amdhsa -module-summary %s -o %t1.bc
+; RUN: opt -mtriple=amdgcn-amd-amdhsa -module-summary %p/Inputs/noinline.ll -o %t2.bc
+; RUN: llvm-lto -thinlto-action=thinlink -force-import-all %t1.bc %t2.bc -o %t3.index.bc
+; RUN: llvm-lto -thinlto-action=import -force-import-all %t1.bc %t2.bc --thinlto-index=%t3.index.bc -thinlto-save-temps=%t3.
+; RUN: llvm-dis %t3.0.3.imported.bc -o - | FileCheck %s --check-prefix=MOD1
+; RUN: llvm-dis %t3.1.3.imported.bc -o - | FileCheck %s --check-prefix=MOD2
+
+define i32 @f1(ptr %p) #0 {
+entry:
+  call void @f2(ptr %p)
+  ret i32 0
+}
+
+define weak hidden void @f3(ptr %v) #0 {
+entry:
+  store i32 12345, ptr %v
+  ret void
+}
+
+declare void @f2(ptr)
+
+attributes #0 = { noinline }
+
+; MOD1: define weak hidden void @f3
+; MOD1: define available_externally void @f2
+; MOD2: define void @f2
+; MOD2: define available_externally hidden void @f3

llvm/test/ThinLTO/AMDGPU/lit.local.cfg

@@ -0,0 +1,2 @@
+if not "AMDGPU" in config.root.targets:
+    config.unsupported = True