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Given the following code:
(module
(import "External" "external_function" (func $external_function))
(func $foo (param $0 i32) (param $1 i32) (result i32)
i32.const 0)
(func $_start (param $0 i32) (param $1 i64) (param $2 i32) (param $3 i32)
i32.const 0
i32.load
local.set $0
local.get $0
local.set $2
i32.const 0
i32.const 0
call $foo
local.set $0
block ;; label = @1
local.get $0
br_if 0 (;@1;)
i32.const 0
i32.const 0
i32.store
i32.const 0
local.set $3
end
local.get $3
local.set $0
local.get $2
local.get $0
i32.and
local.set $0
block ;; label = @1
local.get $0
i32.eqz
br_if 0 (;@1;)
call $external_function
end)
(memory $0 258 258)
(export "_start" (func $_start)))wasm-opt (e6d02fa) by -all -O3 cannot deduce the condition
(i32.and
(i32.load
(i32.const 0)
)
(block (result i32)
(i32.store
(i32.const 0)
(i32.const 0)
)
(i32.const 0)
)to zero (but -all -O2 can), thus misses an optimization opportunity.
Similar to #7455 and #7556, I think the probably cause is the limitation of merge-blocks, which cannot hoist the constant in the block out due to the load and store instructions cannot reordered. Below the is logic code checking whether a given binary operation emits zero bits:
binaryen/src/passes/OptimizeInstructions.cpp
Lines 317 to 327 in e6d02fa
Currently the above logic cannot deduce the condition above to zero, since the getMaxBits does not handle the Block expression. Do you think there is a need to extend the getMaxBits to handle the Block?
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