Miscompile with multivalue ABI

[nikic]

From rust-lang/rust#127318:

; RUN: llc -mtriple=wasm32-unknown-unknown -target-abi=experimental-mv
define i64 @test() {
entry:
  %pair = call { i64, i64 } @foo()
  %v0 = extractvalue { i64, i64 } %pair, 0
  %1 = icmp eq i64 %v0, 0
  %v1 = extractvalue { i64, i64 } %pair, 1
  %_0.sroa.0.0 = select i1 %1, i64 42, i64 %v1
  ret i64 %_0.sroa.0.0
}

declare { i64, i64 } @foo()

Results in:

	i64.const	42
	local.get	0
	call	foo
	local.set	0
	i64.eqz
	i64.select

Note the get-before-set of local 0.

[llvmbot]

@llvm/issue-subscribers-backend-webassembly

Author: Nikita Popov (nikic)

From https://github.com/rust-lang/rust/issues/127318:

; RUN: llc -mtriple=wasm32-unknown-unknown -target-abi=experimental-mv
define i64 @<!-- -->test() {
entry:
  %pair = call { i64, i64 } @<!-- -->foo()
  %v0 = extractvalue { i64, i64 } %pair, 0
  %1 = icmp eq i64 %v0, 0
  %v1 = extractvalue { i64, i64 } %pair, 1
  %_0.sroa.0.0 = select i1 %1, i64 42, i64 %v1
  ret i64 %_0.sroa.0.0
}

declare { i64, i64 } @<!-- -->foo()

Results in:

	i64.const	42
	local.get	0
	call	foo
	local.set	0
	i64.eqz
	i64.select

Note the get-before-set of local 0.

[temeddix]

Is there any update on this issue? This bug is kind of severe, as any feature that use multivalue ABI like u128 leads to maximum call stack error.

This affect many features including:

• Rust's std::time::Duration
• chrono crate

[tlively]

Can you work around the issue by not using multivalue for now?