[WebAssembly] Fix tail call with return_call_indirect instruction

[yamt]

Summary

A musttail with function pointers doesn't rewind C stack without this.

[asb]

Are you able to provide a test case that demonstrates the codegen change?

[yamt]

In D142615#4090795, @asb wrote:

Are you able to provide a test case that demonstrates the codegen change?

this function is broken without this change: https://github.com/yamt/garbage/blob/51ec5aaea4e30c9eece7665dea78cb71364076e2/wasm/tail-call/b.c#L12

do you mean adding a test case in llvm tree? i'm not familiar with it. if you mean so, can you point me where to add?

[yamt]

In D142615#4090846, @yamt wrote:

In D142615#4090795, @asb wrote:

Are you able to provide a test case that demonstrates the codegen change?

this function is broken without this change: https://github.com/yamt/garbage/blob/51ec5aaea4e30c9eece7665dea78cb71364076e2/wasm/tail-call/b.c#L12

sorry, i linked to a wrong function.
actually this function: https://github.com/yamt/garbage/blob/51ec5aaea4e30c9eece7665dea78cb71364076e2/wasm/tail-call/a.c#L7

[yamt]

i added a test.

[yamt]

remove an unnecessary line in the test

[aheejin]

LGTM % comment

llvm/test/CodeGen/WebAssembly/tailcall.ll

260

Can you add a little more comment that says this test is to test if SP restoring code is generated correctly before the return_call?

[aheejin]

FYI, not sure why this hasn't landed so far, but D146569 is fixing the same issue.

[yamt]

add comment

[yamt]

llvm/test/CodeGen/WebAssembly/tailcall.ll

260

done

[aheejin]

Thanks for fixing this, but D146569 has landed first.

llvm/lib/Target/WebAssembly/WebAssemblyInstrCall.td

 
 let isReturn = 1, isTerminator = 1, hasCtrlDep = 1, isBarrier = 1 in
 defm RET_CALL :
   I<(outs), (ins function32_op:$callee, variable_ops),
     (outs), (ins function32_op:$callee), [],
     "return_call    \t$callee", "return_call\t$callee", 0x12>,
   Requires<[HasTailCall]>;
 
-let isReturn = 1 in
+let isReturn = 1, isTerminator = 1, hasCtrlDep = 1, isBarrier = 1 in
 defm RET_CALL_INDIRECT :
   I<(outs), (ins TypeIndex:$type, table32_op:$table, variable_ops),
     (outs), (ins TypeIndex:$type, table32_op:$table), [],
     "return_call_indirect\t", "return_call_indirect\t$type, $table",
     0x13>,
   Requires<[HasTailCall]>;
 
 } // Uses = [SP32,SP64], isCall = 1

llvm/test/CodeGen/WebAssembly/tailcall.ll

 ; YAML-NEXT:    ReturnTypes:
 ; YAML-NEXT:      - I32
 define i32 @unique_caller(ptr %p) {
   %f = load ptr, ptr %p
   %v = tail call i32 %f(i32 0, float 0., i64 0, double 0.)
   ret i32 %v
 }
 
+; Test if SP restoring code is generated correctly before the return_call_indirect.
+; Note: the second global.set is to restore the SP.
+; CHECK-LABEL: alloca_and_indirect_tail_call
+; CHECK: global.get $push{{[0-9]+}}=, __stack_pointer
+; CHECK: global.set __stack_pointer, $pop{{[0-9]+}}
+; CHECK: global.set __stack_pointer, $pop{{[0-9]+}}
+; CHECK: return_call_indirect , $0, $1
+declare void @do_something(ptr)
+define i32 @alloca_and_indirect_tail_call(ptr %p) {
+  ; consume stack
+  %a = alloca i8
+  call void @do_something(ptr %a)
+
+  %f = load ptr, ptr %p
+  %v = musttail call i32 %f(ptr %p)
+  ret i32 %v
+}
+
 ; CHECK-LABEL: .section .custom_section.target_features
 ; CHECK-NEXT: .int8 1
 ; CHECK-NEXT: .int8 43
 ; CHECK-NEXT: .int8 9
 ; CHECK-NEXT: .ascii "tail-call"