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Backport 7882 to release-18.0.0 #7885

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Merged
elliottt merged 1 commit into from
Feb 7, 2024
Merged

Backport 7882 to release-18.0.0 #7885

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26 changes: 17 additions & 9 deletions cranelift/codegen/src/opts/extends.isle
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Original file line number Diff line number Diff line change
Expand Up @@ -77,18 +77,26 @@

;; Matches values where `ireducing` them will not actually introduce another
;; instruction, since other rules will collapse them with the reduction.
(decl pure multi will_simplify_with_ireduce (Value) Value)
(rule (will_simplify_with_ireduce x@(uextend _ _)) x)
(rule (will_simplify_with_ireduce x@(sextend _ _)) x)
(rule (will_simplify_with_ireduce x@(iconst _ _)) x)
(rule (will_simplify_with_ireduce x@(unary_op _ _ a))
(if-let _ (will_simplify_with_ireduce a))
(decl pure multi will_simplify_with_ireduce_rec (u8 Value) Value)
(rule (will_simplify_with_ireduce_rec _ x@(uextend _ _)) x)
(rule (will_simplify_with_ireduce_rec _ x@(sextend _ _)) x)
(rule (will_simplify_with_ireduce_rec _ x@(iconst _ _)) x)
(rule (will_simplify_with_ireduce_rec depth x@(unary_op _ _ a))
(if-let _ (u8_lt 0 depth))
(if-let _ (reducible_modular_op x))
(if-let _ (will_simplify_with_ireduce_rec (u8_sub depth 1) a))
x)
(rule (will_simplify_with_ireduce x@(binary_op _ _ a b))
(if-let _ (will_simplify_with_ireduce a))
(if-let _ (will_simplify_with_ireduce b))
(rule (will_simplify_with_ireduce_rec depth x@(binary_op _ _ a b))
(if-let _ (u8_lt 0 depth))
(if-let _ (reducible_modular_op x))
(if-let _ (will_simplify_with_ireduce_rec (u8_sub depth 1) a))
(if-let _ (will_simplify_with_ireduce_rec (u8_sub depth 1) b))
x)

(decl pure multi will_simplify_with_ireduce (Value) Value)
(rule (will_simplify_with_ireduce x)
(will_simplify_with_ireduce_rec 2 x))

;; Matches values where the high bits of the input don't affect lower bits of
;; the output, and thus the inputs can be reduced before the operation rather
;; than doing the wide operation then reducing afterwards.
Expand Down
38 changes: 38 additions & 0 deletions cranelift/filetests/filetests/egraph/associative-and-commutative.clif
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Expand Up @@ -79,3 +79,41 @@ block0(v0: i32, v1: i32, v2: i32, v3: i32):
; nextln: v8 = bxor v4, v7
; check: return v8
}

;; We don't have any assertions about the result of optimizing this function,
;; but it's a good canary for unbounded recursion in optimization rulesets. In
;; particular, because of the shared structure in the dag, it won't be obvious
;; to rules that are pattern matching on trees that this is actually a chain,
;; and they will exhibit exponential behavior as a result.
function %iadd_big_chain(i8) -> i16 {
block0(v0: i8):
v1 = uextend.i32 v0
v2 = iconst.i32 42
v3 = iadd v1, v2
v4 = iadd v3, v3
v5 = iadd v4, v4
v6 = iadd v5, v5
v7 = iadd v6, v6
v8 = iadd v7, v7
v9 = iadd v8, v8
v10 = iadd v9, v9
v11 = iadd v10, v10
v12 = iadd v11, v11
v13 = iadd v12, v12
v14 = iadd v13, v13
v15 = iadd v14, v14
v16 = iadd v15, v15
v17 = iadd v16, v16
v18 = iadd v17, v17
v19 = iadd v18, v18
v20 = iadd v19, v19
v21 = iadd v20, v20
v22 = iadd v21, v21
v23 = iadd v22, v22
v24 = iadd v23, v23
v25 = iadd v24, v24
v26 = iadd v25, v25
v27 = iadd v26, v26
v28 = ireduce.i16 v27
return v28
}