R E C U R S I O N I N L I N I N G I N L L V M - - PowerPoint PPT Presentation

R E C U R S I O N I N L I N I N G I N L L V M

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• Performance improvements observed of up to ~20%.
• Potentially improve chances for other optimization passes:
• Increase function size.
• Increase knowledge of the context.
• Current status:
• GCC inlines recursive function calls up to a certain depth.
• LLVM marks recursive functions as noinline.
• Code size and register pressure must be controlled.

# 1 I n l i n e i t e r a t i v e l y

f(x): if x == 0 return 1 a = g(x) b = f(a) return a + h(b) f(x): if x == 0 return 1 a = g(x) if a == 0 b = 1 else: a1 = g(a) b1 = f(a1) b = a1 + h(b1) return a + h(b)

L e v e l 1 i n l i n e

# 2 R e m

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f(x): if x == 0 return 1 a = g(x) b = f(a) return a + h(b) f(x): x1 = x while x1 != 0: a = g(x) x1 = a push(a) b = 1 while S not empty: a = pop() b = a + h(b) return b a i s l i v e

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3 ) 1 . 1 . 9 7 S t a c k 2 . 5 3 1 . 1 9 I t e r a t i v e i n l i n i n g 1 . 1 . 4 G C C C l a n g B a s e (

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3 ) 3 . 5 2 . 5 4 S t a c k 2 . 6 7 2 . 7 1 I t e r a t i v e i n l i n i n g 3 . 5 2 . 7 4

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C C b a s e O b j e c t s i z e ( k B )