[WebAssembly] Add mechanisms for specifying an explicit import module name.

This adds a wasm-import-module function attribute and a .import_module
assembler directive, for specifying module import names for WebAssembly.
Currently these may only be used for function symbols; global variables
may be considered in the future.

WebAssembly has a two-level namespace scheme for symbols, and it's
normally the linker's job to assign the module name, which is the
first-level name. The attributes here allow users to specify their
own module names explicitly, which is useful for tools generating
bindings to modules defined in other languages.

This feature is not fully usable yet. It will evolve along with the
ongoing symbol table and lld changes.

Differential Revision: https://reviews.llvm.org/D42520

llvm-svn: 324778

2 files changed, 27 insertions, 1 deletions

diff --git a/llvm/test/CodeGen/WebAssembly/import-module.ll b/llvm/test/CodeGen/WebAssembly/import-module.ll
new file mode 100644
index 00000000000..e748b7ec1c7
--- /dev/null
+++ b/llvm/test/CodeGen/WebAssembly/import-module.ll
@@ -0,0 +1,19 @@
+; RUN: llc < %s -asm-verbose=false | FileCheck %s
+
+target datalayout = "e-m:e-p:32:32-i64:64-n32:64-S128"
+target triple = "wasm32-unknown-unknown-wasm"
+
+define void @test() {
+  call void @foo()
+  call void @plain()
+  ret void
+}
+
+declare void @foo() #0
+declare void @plain()
+
+attributes #0 = { "wasm-import-module"="bar" }
+
+; CHECK-NOT: .import_module plain
+;     CHECK: .import_module foo, bar
+; CHECK-NOT: .import_module plain
diff --git a/llvm/test/MC/WebAssembly/external-func-address.ll b/llvm/test/MC/WebAssembly/external-func-address.ll
index 940f54cb077..05a335b848a 100644
--- a/llvm/test/MC/WebAssembly/external-func-address.ll
+++ b/llvm/test/MC/WebAssembly/external-func-address.ll
@@ -5,6 +5,11 @@ target triple = "wasm32-unknown-unknown-wasm"
 ; Verify that addresses of external functions generate correctly typed
 ; imports and relocations or type R_TABLE_INDEX_I32.
 
+declare void @f0(i32) #0
+@ptr_to_f0 = hidden global void (i32)* @f0, align 4
+
+attributes #0 = { "wasm-import-module"="somewhere" }
+
 declare void @f1(i32) #1
 @ptr_to_f1 = hidden global void (i32)* @f1, align 4
 
@@ -24,6 +29,8 @@ declare void @f1(i32) #1
 ; CHECK-NEXT:         Field:           __linear_memory
 ; CHECK:            - Module:          env
 ; CHECK-NEXT:         Field:           __indirect_function_table
+; CHECK:            - Module:          somewhere
+; CHECK-NEXT:         Field:           f0
 ; CHECK:            - Module:          env
 ; CHECK-NEXT:         Field:           f1
 ; CHECK-NEXT:         Kind:            FUNCTION
@@ -33,7 +40,7 @@ declare void @f1(i32) #1
 ; CHECK-NEXT:       - Offset:
 ; CHECK-NEXT:           Opcode:          I32_CONST
 ; CHECK-NEXT:           Value:           1
-; CHECK-NEXT:         Functions:       [ 0 ]
+; CHECK-NEXT:         Functions:       [ 0, 1 ]
 ; CHECK:        - Type:            DATA
 ; CHECK-NEXT:     Relocations:
 ; CHECK-NEXT:       - Type:            R_WEBASSEMBLY_TABLE_INDEX_I32