[WebAssembly] Add extra test for weak global symbols

[ncw]

Summary

Currently the test only checks behaviour for weak function symbols.

Should be good to merge straight away?

[ncw]

Oops, rebased to master than on top of my previous patches

[sbc100]

Nice. I wonder if we added --emit-reloc is might show more clearly which address is being loaded by the code section? Happy to land either way.

[ncw]

Since the relocation is emitted in the function body, which is tested, it should be good enough for now.

D41390 modifies this test (by discarding the duplicate InputSegment), at which point the test is even more precise. Until D41390 lands, this test doesn't need to be too precise since it's currently asserting "wrong" output (both copies of the weak functions and weak globals are there in the CODE/DATA sections).

I'd say it's fine to commit this as-is - we're revisiting it soon.

test/wasm/Inputs/weak-symbol1.ll

 define weak i32 @weakFn() #0 {
 entry:
   ret i32 1
 }
 
 define i32 @exportWeak1() {
 entry:
     ret i32 ptrtoint (i32 ()* @weakFn to i32)
 }
+
+@weakGlobal = weak global i32 1

test/wasm/Inputs/weak-symbol2.ll

 define weak i32 @weakFn() #0 {
 entry:
   ret i32 2
 }
 
 define i32 @exportWeak2() {
 entry:
     ret i32 ptrtoint (i32 ()* @weakFn to i32)
 }
+
+@weakGlobal = weak global i32 2

test/wasm/weak-symbols.ll

 ; RUN: llc -filetype=obj -mtriple=wasm32-unknown-unknown-wasm %p/Inputs/weak-symbol1.ll -o %t1.o
 ; RUN: llc -filetype=obj -mtriple=wasm32-unknown-unknown-wasm %p/Inputs/weak-symbol2.ll -o %t2.o
 ; RUN: llc -filetype=obj -mtriple=wasm32-unknown-unknown-wasm %s -o %t.o
 ; RUN: lld -flavor wasm -o %t.wasm %t.o %t1.o %t2.o
 ; RUN: obj2yaml %t.wasm | FileCheck %s
 
 declare i32 @weakFn() local_unnamed_addr
+@weakGlobal = external global i32
 
-define void @_start() local_unnamed_addr {
+define i32 @_start() local_unnamed_addr {
 entry:
   %call = call i32 @weakFn()
-  ret void
+  %val = load i32, i32* @weakGlobal, align 4
+  ret i32 %val
 }
 
 ; CHECK:      --- !WASM
 ; CHECK-NEXT: FileHeader:
 ; CHECK-NEXT:   Version:         0x00000001
 ; CHECK-NEXT: Sections:
 ; CHECK-NEXT:   - Type:            TYPE
 ; CHECK-NEXT:     Signatures:
 ; CHECK-NEXT:       - Index:           0
-; CHECK-NEXT:         ReturnType:      NORESULT
-; CHECK-NEXT:         ParamTypes:
-; CHECK-NEXT:       - Index:           1
 ; CHECK-NEXT:         ReturnType:      I32
 ; CHECK-NEXT:         ParamTypes:
 ; CHECK-NEXT:   - Type:            FUNCTION
-; CHECK-NEXT:     FunctionTypes:   [ 0, 1, 1, 1 ]
+; CHECK-NEXT:     FunctionTypes:   [ 0, 0, 0, 0 ]
 ; CHECK-NEXT:   - Type:            TABLE
 ; CHECK-NEXT:     Tables:
 ; CHECK-NEXT:       - ElemType:        ANYFUNC
 ; CHECK-NEXT:         Limits:
 ; CHECK-NEXT:           Flags:           [ HAS_MAX ]
 ; CHECK-NEXT:           Initial:         0x00000002
 ; CHECK-NEXT:           Maximum:         0x00000002
 ; CHECK-NEXT:   - Type:            MEMORY
 ; CHECK-NEXT:     Memories:
 ; CHECK-NEXT:       - Initial:         0x00000002
 ; CHECK-NEXT:   - Type:            GLOBAL
 ; CHECK-NEXT:     Globals:
 ; CHECK-NEXT:       - Type:            I32
 ; CHECK-NEXT:         Mutable:         true
 ; CHECK-NEXT:         InitExpr:
 ; CHECK-NEXT:           Opcode:          I32_CONST
-; CHECK-NEXT:           Value:           66560
+; CHECK-NEXT:           Value:           66576
 ; CHECK-NEXT:   - Type:            EXPORT
 ; CHECK-NEXT:     Exports:
 ; CHECK-NEXT:       - Name:            memory
 ; CHECK-NEXT:         Kind:            MEMORY
 ; CHECK-NEXT:         Index:           0
 ; CHECK-NEXT:       - Name:            _start
 ; CHECK-NEXT:         Kind:            FUNCTION
 ; CHECK-NEXT:         Index:           0

 ; CHECK-NEXT:     Segments:
 ; CHECK-NEXT:       - Offset:
 ; CHECK-NEXT:           Opcode:          I32_CONST
 ; CHECK-NEXT:           Value:           1
 ; CHECK-NEXT:         Functions:       [ 1 ]
 ; CHECK-NEXT:   - Type:            CODE
 ; CHECK-NEXT:     Functions:
 ; CHECK-NEXT:       - Locals:
-; CHECK-NEXT:         Body:            1081808080001A0B
+; CHECK-NEXT:         Body:            1081808080001A4100280280888080000B
 ; CHECK-NEXT:       - Locals:
 ; CHECK-NEXT:         Body:            41010B
 ; CHECK-NEXT:       - Locals:
 ; CHECK-NEXT:         Body:            4181808080000B
 ; CHECK-NEXT:       - Locals:
 ; CHECK-NEXT:         Body:            4181808080000B
+; CHECK-NEXT:   - Type:            DATA
+; CHECK-NEXT:     Segments:
+; CHECK-NEXT:       - SectionOffset:   7
+; CHECK-NEXT:         MemoryIndex:     0
+; CHECK-NEXT:         Offset:
+; CHECK-NEXT:           Opcode:          I32_CONST
+; CHECK-NEXT:           Value:           1024
+; CHECK-NEXT:         Content:         '0100000002000000'
 ; CHECK-NEXT:   - Type:            CUSTOM
 ; CHECK-NEXT:     Name:            linking
-; CHECK-NEXT:     DataSize:        0
+; CHECK-NEXT:     DataSize:        8
 ; CHECK-NEXT:   - Type:            CUSTOM
 ; CHECK-NEXT:     Name:            name
 ; CHECK-NEXT:     FunctionNames:
 ; CHECK-NEXT:       - Index:           0
 ; CHECK-NEXT:         Name:            _start
 ; CHECK-NEXT:       - Index:           2
 ; CHECK-NEXT:         Name:            exportWeak1
 ; CHECK-NEXT:       - Index:           3
 ; CHECK-NEXT:         Name:            exportWeak2
 ; CHECK-NEXT: ...