Enhancing the Role of Inlining in Effective Interprocedural Parallelization Jichi Guo, Mike Stiles Qing Yi, Kleanthis Psarris

Problem Inter-procedural parallelization o Parallel after inlining Gain more parallelizable loops Lost of parallelized loops o Inlining messes up caller / callee Missed parallel opportunities o Inlining increases code complexity

Goal Keep the gain parallelizable loops Prevent the lost parallelism Discover the missed opportunities

Solution Summarize the code using annotation o Express the underlying information Inline the annotation before parallelization o Pass the summarized information to the compiler Reverse -inline after parallelization o Revert inlining side effects o Maintain equivalence

Outline Innovations Problems of parallel + inline strategy Annotation language Annotation-based inlining technique Experiments Summary

Outline Innovations Problems of parallel + inline strategy Annotation language Annotation-based inlining technique Experiments Summary

Problems of parallel + inlining Parallel + inlining o Conventional inlining with heuristics and pre-transformations Heuristics: code size Transformations: linearization, forward substitution o Intra-procedural loop parallelization Fortran do-all loop Goal o Gain loops in caller Problems o Lost loops in caller / callee o Missed loops in caller

Problems of parallel + inlining Lost of parallelizable loops in caller/callee o Transformations that cause the lost Forward substitution Linearization Forward substitution of non-linear subscripts o Create indirect array references Linearization of array dimensions o Mess up array shapes

Problems of parallel + inlining Forward substitution of non-linear subscripts o Create indirect array references X2(I) ⇒ T(IX(7) + I) Y2(I) ⇒ T(IX(8) + I) Z2(I) ⇒ T(IX(9) + I)

Problems of parallel + inlining Linearization of array dimensions o Mess up array shapes PP(i, j, k) ⇒ PP(i + j*4 + k*16)

Problems of parallel + inlining Missed parallelizable loops in caller o Coding styles that cause the lost Opaque compositional subroutines o A calls B, B calls C, C calls D, … Array access o When it is difficult to determine which part is killed Debugging and Error Checking o Statement that breaks the dependency is never executed I/O statements Indirect array references o ID=IDX(I), X = A(ID)

Problems of parallel + inlining Opaque compositional subroutines o A calls B, B calls C, C calls D, …

Problems of parallel + inlining Array access o Difficult to determine which part is killed CTR computed at runtime

Problems of parallel + inlining Debugging and Error Checking o Statement that breaks the dependency is never executed I/O statements

Problems of parallel + inlining Indirect array references IN=>NODE NODE=>IREL IREL=>RHSB

Outline Innovations Problems of parallel + inline strategy Annotation language Annotation-based inlining technique Experiments Summary

The annotation language Goal o Summarize information o Avoid ambiguity

The annotation language Restricted grammar Special operators Writing annotations

The annotation language Restricted grammar o Do-all loop only o No goto

The annotation language Special operators y = operator(x1, x2, …, xn) Purpose: abstract relation o Unknown operator Relation is unknown o Generic functions o Unique operator Relation is one-to-one, from X to Y

The annotation language Writing annotations o Eliminating adverse side effects Preserve caller and callee if inlining breaks the dependency o Summarize opaque subroutines Eliminate nested function calls o Array access Specify exact range get read/modified o Debugging and error handling Aggressive strategy: ignore checking statements o Indirect array references Discover unique relation

The annotation language Summarize opaque subroutines o Eliminate nested function calls

The annotation language Array access o Specify exact range get read/modified

The annotation language Debugging and error handling o Aggressive strategy: ignore checking statements

The annotation language Indirect array references o Discover unique relation

Outline Innovations Problems of parallel + inline strategy Annotation language Annotation-based inlining technique Experiments Summary

Annotation-based inlining Goal o Pass annotated information to the compiler o Eliminate inlining side effects Flow o Inline before parallelization o Reverse-inlining after parallelization o Verify and evaluate at last Implementation o POLARIS compiler for parallelization o ROSE compiler for parsing o POET transformer o PERFECT benchmark

Annotation-based inlining Workflow o Annotation inlining ⇒ Parallelization ⇒ Reverse-inlining

Annotation-based inlining Inlining annotation o Steps Annotation ⇒ source language o Translating special operators Inlinining generated source language o Avoiding linearization o Translating special operators Unknown: using uninitialized global arrays Unique: using linear expression o Avoiding linearization

Annotation-based inlining Inlining annotation

Annotation-based inlining Parallelize do-all loops

Annotation-based inlining Reverse inlining

Annotation-based inlining Reverse inlining is indispensible o Inlinining is restored to function call Avoid lost of parallelism in caller / callee Enable abstraction operators (unknown, unique)

Annotation-based inlining Verification and evaluation o Correctness, Efficiency, and Generality

Outline Innovations Problems of parallel + inline strategy Annotation language Annotation-based inlining technique Experiments Summary

Experiment Purpose o What does conventional lining bring to parallelization Gain? Lost? Missed? o How good is annotation-based inlining to avoid above issues Design o PERFECT benchmarks (except SPEC77) o Two machines 8 cores Intel Mac 4 cores AMD Operon o End compiler GFortran IFort 11.1 Result o Count of Loops o Performance

Experiment Result: Loops o Conventional inlining Having loss o Annotation-based inlining No loss, more gain

Experiment Result: Performance o Average speedup limited o Annot-based inlining always better

Summary Inter-procedural parallelization Summarize effects of conventional inlining o Gain o Lost o Missed Propose annotation-based inlining o Annotation summary o Enhanced inlining strategy o Reverse inlining

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