BPVM Snack Pack #15 - Optimizations: Making Your Blueprint Faster
The compiler doesn't just translate your nodes - it optimizes them! Learn about the clever tricks that make your compiled Blueprint run faster.
The content in this post is based on Unreal Engine 5.6.0
BPVM Snack Pack - Quick Blueprint knowledge drops! Part of the Blueprint to Bytecode series.
The Optimization Phase
After scheduling but before bytecode generation, the compiler optimizes your statements:
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void PostcompileFunction(Context) {
Context.ResolveStatements(); // Optimization happens here!
// Inside ResolveStatements:
FinalSortLinearExecList(); // Re-order for efficiency
ResolveGoToFixups(); // Fix jump targets
MergeAdjacentStates(); // Combine operations
}
Your code gets faster without you doing anything!
Optimization #1: Merge Adjacent States
Remove redundant push/pop operations:
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// Before optimization
PushState(Label_A)
PopState()
PushState(Label_B)
// After optimization
PushState(Label_B) // First two removed!
Why it matters: Flow stack operations are expensive. Fewer = faster!
Optimization #2: Remove Redundant Jumps
Eliminate useless jumps:
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// Before
Goto Label_A
Label_A: // Jump target right here!
DoSomething()
// After
DoSomething() // Jump removed!
Why it matters: Every jump has overhead. No jump = instant execution!
Optimization #3: Dead Code Elimination
Remove code that never runs:
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// Before
Return
CallFunction() // Never reached!
SetVariable() // Never reached!
// After
Return // Everything after removed!
Why it matters: Why generate bytecode that never executes?
Optimization #4: Constant Folding
Pre-calculate constant expressions:
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// Before
Result = 5 + 10 + 15
// After
Result = 30 // Calculated at compile time!
Why it matters: Why waste CPU cycles on math you already know?
Optimization #5: Jump Chain Collapsing
Simplify jump chains:
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// Before
JumpIfFalse Label_A
Label_A: Jump Label_B
Label_B: Jump Label_C
Label_C: DoSomething()
// After
JumpIfFalse Label_C // Direct jump!
DoSomething()
Why it matters: Each jump takes time. One jump instead of three!
Optimization #6: Flow Stack vs Direct Return
Choose the faster path:
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// Complex flow (needs flow stack)
BeginPlay → Branch
True → DoA → EndOfThread
False → DoB → EndOfThread
// Simple flow (direct return)
BeginPlay → DoSimpleStuff → Return // No flow stack!
Why it matters: Flow stack management is slow. Direct return is fast!
The MergeAdjacentStates Algorithm
This is the most impactful optimization:
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void MergeAdjacentStates() {
for (int i = 0; i < Statements.Num(); i++) {
Statement* Current = Statements[i];
Statement* Next = Statements[i+1];
// Pattern: Push then Pop
if (Current->Type == KCST_PushState &&
Next->Type == KCST_EndOfThread) {
// Remove both!
Statements.RemoveAt(i, 2);
i--;
}
// Pattern: Jump to next statement
if (Current->Type == KCST_UnconditionalGoto &&
Current->TargetLabel == Next->Label) {
// Remove jump!
Statements.RemoveAt(i);
i--;
}
}
}
Real-World Impact
Before optimization:
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15 statements
8 jumps
4 flow stack operations
Bytecode size: 512 bytes
After optimization:
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10 statements (33% fewer!)
3 jumps (62% fewer!)
1 flow stack operation (75% fewer!)
Bytecode size: 320 bytes (37% smaller!)
Result: Faster execution AND smaller memory footprint!
Pure Node Optimization
Pure nodes get special treatment:
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// If output never used
GetRandomFloat() // REMOVED!
// If output used once
GetRandomFloat() → Add → Print
// All inlined together!
Why it matters: Don’t compute values nobody needs!
Branch Prediction Hints
The compiler tries to optimize branches:
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// Most common pattern
if (IsValid()) { // Likely true
DoStuff();
} else { // Rarely happens
HandleError();
}
// Compiler arranges:
CheckIsValid()
JumpIfFalse Error_Label // Unlikely jump
DoStuff()
Jump End_Label
Error_Label: HandleError() // Cold code
End_Label:
Why it matters: CPU branch prediction works better!
Optimization Limits
Some things can’t be optimized:
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// Can't optimize external calls
CallBlueprintFunction() // Unknown behavior
// Can't optimize dynamic casts
Cast<AMyActor>(GetActor()) // Runtime check
// Can't optimize user-facing debug sites
BreakPoint() // Must preserve for debugging!
The Performance Impact
Typical optimization gains:
- 10-20% faster execution
- 20-30% smaller bytecode
- Fewer VM overhead operations
- Better cache locality
Not dramatic, but completely free!
Quick Takeaway
- Compiler automatically optimizes your Blueprint
- MergeAdjacentStates removes redundant flow operations
- Jump elimination makes control flow faster
- Dead code removal shrinks bytecode size
- Constant folding pre-calculates known values
- Typical gain: 10-20% faster, 20-30% smaller
- You get these benefits for free!
The Silent Optimizer
Next time you compile a Blueprint, remember that the compiler isn’t just translating your nodes - it’s actively making them faster. It’s like having an expert programmer review and optimize every function you write, automatically!
Want More Details?
For complete optimization breakdown:
Next: Learning to read the actual bytecode!
🍿 BPVM Snack Pack Series
- ← #14: Backend Magic
- #15: Optimizations Explained ← You are here
- #16: Reading Bytecode →