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Merged
merged 1 commit into from
Nov 8, 2023
+45 −47
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LocalCSE: Do not optimize small things like global.get #6087

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9 changes: 6 additions & 3 deletions src/passes/LocalCSE.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -334,13 +334,16 @@ struct Scanner
// and so adding one set+one get and removing one of the items itself
// is not detrimental, and may be beneficial.
// TODO: investigate size 2
if (options.shrinkLevel > 0 && Measurer::measure(curr) >= 3) {
auto size = Measurer::measure(curr);
if (options.shrinkLevel > 0 && size >= 3) {
return true;
}

// If we focus on speed, any reduction in cost is beneficial, as the
// cost of a get is essentially free.
if (options.shrinkLevel == 0 && CostAnalyzer(curr).cost > 0) {
// cost of a get is essentially free. However, we need to balance that with
// the fact that the VM will also do CSE/GVN itself, so minor improvements
// are not worthwhile, so skip things of size 1 (like a global.get).
if (options.shrinkLevel == 0 && CostAnalyzer(curr).cost > 0 && size >= 2) {
return true;
}

Expand Down
68 changes: 31 additions & 37 deletions test/lit/passes/inlining-optimizing_optimize-level=3.wast
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Original file line number Diff line number Diff line change
Expand Up @@ -299,13 +299,11 @@
;; CHECK-NEXT: (local $12 i32)
;; CHECK-NEXT: (local $13 i32)
;; CHECK-NEXT: (local.set $8
;; CHECK-NEXT: (local.tee $4
;; CHECK-NEXT: (global.get $STACKTOP)
;; CHECK-NEXT: )
;; CHECK-NEXT: (global.get $STACKTOP)
;; CHECK-NEXT: )
;; CHECK-NEXT: (global.set $STACKTOP
;; CHECK-NEXT: (i32.add
;; CHECK-NEXT: (local.get $4)
;; CHECK-NEXT: (global.get $STACKTOP)
;; CHECK-NEXT: (i32.const 16)
;; CHECK-NEXT: )
;; CHECK-NEXT: )
Expand All @@ -316,11 +314,12 @@
;; CHECK-NEXT: )
;; CHECK-NEXT: (call $abort)
;; CHECK-NEXT: )
;; CHECK-NEXT: (local.set $6
;; CHECK-NEXT: (global.get $STACKTOP)
;; CHECK-NEXT: )
;; CHECK-NEXT: (global.set $STACKTOP
;; CHECK-NEXT: (i32.add
;; CHECK-NEXT: (local.tee $4
;; CHECK-NEXT: (global.get $STACKTOP)
;; CHECK-NEXT: )
;; CHECK-NEXT: (global.get $STACKTOP)
;; CHECK-NEXT: (i32.const 16)
;; CHECK-NEXT: )
;; CHECK-NEXT: )
Expand All @@ -332,19 +331,20 @@
;; CHECK-NEXT: (call $abort)
;; CHECK-NEXT: )
;; CHECK-NEXT: (i32.store
;; CHECK-NEXT: (local.get $4)
;; CHECK-NEXT: (local.get $6)
;; CHECK-NEXT: (local.get $8)
;; CHECK-NEXT: )
;; CHECK-NEXT: (local.set $0
;; CHECK-NEXT: (i32.load
;; CHECK-NEXT: (i32.const 8)
;; CHECK-NEXT: )
;; CHECK-NEXT: )
;; CHECK-NEXT: (local.set $1
;; CHECK-NEXT: (global.get $STACKTOP)
;; CHECK-NEXT: )
;; CHECK-NEXT: (global.set $STACKTOP
;; CHECK-NEXT: (i32.add
;; CHECK-NEXT: (local.tee $1
;; CHECK-NEXT: (global.get $STACKTOP)
;; CHECK-NEXT: )
;; CHECK-NEXT: (global.get $STACKTOP)
;; CHECK-NEXT: (i32.const 224)
;; CHECK-NEXT: )
;; CHECK-NEXT: )
Expand All @@ -361,13 +361,13 @@
;; CHECK-NEXT: (i32.const 120)
;; CHECK-NEXT: )
;; CHECK-NEXT: )
;; CHECK-NEXT: (local.set $5
;; CHECK-NEXT: (local.set $4
;; CHECK-NEXT: (i32.add
;; CHECK-NEXT: (local.get $1)
;; CHECK-NEXT: (i32.const 136)
;; CHECK-NEXT: )
;; CHECK-NEXT: )
;; CHECK-NEXT: (local.set $6
;; CHECK-NEXT: (local.set $5
;; CHECK-NEXT: (i32.add
;; CHECK-NEXT: (local.tee $3
;; CHECK-NEXT: (local.tee $7
Expand All @@ -393,14 +393,14 @@
;; CHECK-NEXT: (i32.const 4)
;; CHECK-NEXT: )
;; CHECK-NEXT: )
;; CHECK-NEXT: (local.get $6)
;; CHECK-NEXT: (local.get $5)
;; CHECK-NEXT: )
;; CHECK-NEXT: )
;; CHECK-NEXT: )
;; CHECK-NEXT: (i32.store
;; CHECK-NEXT: (local.get $2)
;; CHECK-NEXT: (i32.load
;; CHECK-NEXT: (local.get $4)
;; CHECK-NEXT: (local.get $6)
;; CHECK-NEXT: )
;; CHECK-NEXT: )
;; CHECK-NEXT: (drop
Expand Down Expand Up @@ -444,7 +444,7 @@
;; CHECK-NEXT: )
;; CHECK-NEXT: (if
;; CHECK-NEXT: (i32.load
;; CHECK-NEXT: (local.tee $6
;; CHECK-NEXT: (local.tee $5
;; CHECK-NEXT: (i32.add
;; CHECK-NEXT: (local.get $0)
;; CHECK-NEXT: (i32.const 48)
Expand Down Expand Up @@ -473,7 +473,7 @@
;; CHECK-NEXT: )
;; CHECK-NEXT: (i32.store
;; CHECK-NEXT: (local.get $9)
;; CHECK-NEXT: (local.get $5)
;; CHECK-NEXT: (local.get $4)
;; CHECK-NEXT: )
;; CHECK-NEXT: (i32.store
;; CHECK-NEXT: (local.tee $12
Expand All @@ -482,7 +482,7 @@
;; CHECK-NEXT: (i32.const 28)
;; CHECK-NEXT: )
;; CHECK-NEXT: )
;; CHECK-NEXT: (local.get $5)
;; CHECK-NEXT: (local.get $4)
;; CHECK-NEXT: )
;; CHECK-NEXT: (i32.store
;; CHECK-NEXT: (local.tee $11
Expand All @@ -491,10 +491,10 @@
;; CHECK-NEXT: (i32.const 20)
;; CHECK-NEXT: )
;; CHECK-NEXT: )
;; CHECK-NEXT: (local.get $5)
;; CHECK-NEXT: (local.get $4)
;; CHECK-NEXT: )
;; CHECK-NEXT: (i32.store
;; CHECK-NEXT: (local.get $6)
;; CHECK-NEXT: (local.get $5)
;; CHECK-NEXT: (i32.const 80)
;; CHECK-NEXT: )
;; CHECK-NEXT: (i32.store
Expand All @@ -505,7 +505,7 @@
;; CHECK-NEXT: )
;; CHECK-NEXT: )
;; CHECK-NEXT: (i32.add
;; CHECK-NEXT: (local.get $5)
;; CHECK-NEXT: (local.get $4)
;; CHECK-NEXT: (i32.const 80)
;; CHECK-NEXT: )
;; CHECK-NEXT: )
Expand Down Expand Up @@ -547,7 +547,7 @@
;; CHECK-NEXT: (local.get $10)
;; CHECK-NEXT: )
;; CHECK-NEXT: (i32.store
;; CHECK-NEXT: (local.get $6)
;; CHECK-NEXT: (local.get $5)
;; CHECK-NEXT: (i32.const 0)
;; CHECK-NEXT: )
;; CHECK-NEXT: (i32.store
Expand Down Expand Up @@ -586,7 +586,7 @@
;; CHECK-NEXT: (local.get $1)
;; CHECK-NEXT: )
;; CHECK-NEXT: (global.set $STACKTOP
;; CHECK-NEXT: (local.get $4)
;; CHECK-NEXT: (local.get $6)
;; CHECK-NEXT: )
;; CHECK-NEXT: (global.set $STACKTOP
;; CHECK-NEXT: (local.get $8)
Expand Down Expand Up @@ -4080,13 +4080,11 @@
;; CHECK-NEXT: (local $44 i32)
;; CHECK-NEXT: (local $45 i32)
;; CHECK-NEXT: (local.set $13
;; CHECK-NEXT: (local.tee $5
;; CHECK-NEXT: (global.get $STACKTOP)
;; CHECK-NEXT: )
;; CHECK-NEXT: (global.get $STACKTOP)
;; CHECK-NEXT: )
;; CHECK-NEXT: (global.set $STACKTOP
;; CHECK-NEXT: (i32.add
;; CHECK-NEXT: (local.get $5)
;; CHECK-NEXT: (global.get $STACKTOP)
;; CHECK-NEXT: (i32.const 624)
;; CHECK-NEXT: )
;; CHECK-NEXT: )
Expand Down Expand Up @@ -5785,21 +5783,19 @@
;; CHECK-NEXT: (i32.const 0)
;; CHECK-NEXT: )
;; CHECK-NEXT: (f64.store
;; CHECK-NEXT: (local.tee $5
;; CHECK-NEXT: (global.get $tempDoublePtr)
;; CHECK-NEXT: )
;; CHECK-NEXT: (global.get $tempDoublePtr)
;; CHECK-NEXT: (local.get $14)
;; CHECK-NEXT: )
;; CHECK-NEXT: (drop
;; CHECK-NEXT: (i32.load
;; CHECK-NEXT: (local.get $5)
;; CHECK-NEXT: (global.get $tempDoublePtr)
;; CHECK-NEXT: )
;; CHECK-NEXT: )
;; CHECK-NEXT: (local.set $30
;; CHECK-NEXT: (if (result i32)
;; CHECK-NEXT: (i32.lt_s
;; CHECK-NEXT: (i32.load offset=4
;; CHECK-NEXT: (local.get $5)
;; CHECK-NEXT: (global.get $tempDoublePtr)
;; CHECK-NEXT: )
;; CHECK-NEXT: (i32.const 0)
;; CHECK-NEXT: )
Expand Down Expand Up @@ -5844,22 +5840,20 @@
;; CHECK-NEXT: )
;; CHECK-NEXT: )
;; CHECK-NEXT: (f64.store
;; CHECK-NEXT: (local.tee $5
;; CHECK-NEXT: (global.get $tempDoublePtr)
;; CHECK-NEXT: )
;; CHECK-NEXT: (global.get $tempDoublePtr)
;; CHECK-NEXT: (local.get $14)
;; CHECK-NEXT: )
;; CHECK-NEXT: (drop
;; CHECK-NEXT: (i32.load
;; CHECK-NEXT: (local.get $5)
;; CHECK-NEXT: (global.get $tempDoublePtr)
;; CHECK-NEXT: )
;; CHECK-NEXT: )
;; CHECK-NEXT: (local.set $7
;; CHECK-NEXT: (if (result i32)
;; CHECK-NEXT: (i32.lt_u
;; CHECK-NEXT: (i32.and
;; CHECK-NEXT: (i32.load offset=4
;; CHECK-NEXT: (local.get $5)
;; CHECK-NEXT: (global.get $tempDoublePtr)
;; CHECK-NEXT: )
;; CHECK-NEXT: (i32.const 2146435072)
;; CHECK-NEXT: )
Expand Down
15 changes: 8 additions & 7 deletions test/lit/passes/local-cse.wast
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Original file line number Diff line number Diff line change
Expand Up @@ -447,20 +447,17 @@
(global $other-glob (mut i32) (i32.const 1))

;; CHECK: (func $global
;; CHECK-NEXT: (local $0 i32)
;; CHECK-NEXT: (drop
;; CHECK-NEXT: (local.tee $0
;; CHECK-NEXT: (global.get $glob)
;; CHECK-NEXT: )
;; CHECK-NEXT: (global.get $glob)
;; CHECK-NEXT: )
;; CHECK-NEXT: (drop
;; CHECK-NEXT: (local.get $0)
;; CHECK-NEXT: (global.get $glob)
;; CHECK-NEXT: )
;; CHECK-NEXT: (global.set $other-glob
;; CHECK-NEXT: (i32.const 100)
;; CHECK-NEXT: )
;; CHECK-NEXT: (drop
;; CHECK-NEXT: (local.get $0)
;; CHECK-NEXT: (global.get $glob)
;; CHECK-NEXT: )
;; CHECK-NEXT: (global.set $glob
;; CHECK-NEXT: (i32.const 200)
Expand All @@ -470,7 +467,11 @@
;; CHECK-NEXT: )
;; CHECK-NEXT: )
(func $global
;; We should optimize redundant global.get operations.
;; We should not optimize redundant global.get operations: they are of size
;; 1 (no children), and so we may end up increasing code size here for
;; unclear benefit. The benefit is unclear since VMs already do GVN/CSE
;; themselves, and so we focus on things of size 2 and above, where we
;; definitely reduce code size at least.
(drop (global.get $glob))
(drop (global.get $glob))
;; We can do it past a write to another global
Expand Down