CANN/PTO-ISA控制流操作文档

Control Flow Operations

【免费下载链接】pto-isaParallel Tile Operation (PTO) is a virtual instruction set architecture designed by Ascend CANN, focusing on tile-level operations. This repository offers high-performance, cross-platform tile operations across Ascend platforms.项目地址: https://gitcode.com/cann/pto-isa

This document describes structured control flow operations from the MLIRscf(Structured Control Flow) dialect.

Total Operations:9

Loop Operations

scf.for - For Loop

Description:For loop with lower bound, upper bound, and step. Supports loop-carried variables and signed/unsigned comparison.

Syntax:

scf.for %iv = %lb to %ub step %step { // loop body } scf.for %iv = %lb to %ub step %step iter_args(%arg = %init) -> (type) { // loop body with loop-carried variable scf.yield %new_value : type } scf.for unsigned %iv = %lb to %ub step %step : i32 { // unsigned comparison }

Operands:

• lb: Lower bound (index or integer)
• ub: Upper bound (exclusive)
• step: Step value (must be positive)
• iter_args: Initial values for loop-carried variables (optional)

Results:

• Final values of loop-carried variables (if any)

Example:

// Simple loop scf.for %i = %c0 to %c100 step %c1 { // loop body } // Loop with accumulator %sum = scf.for %i = %c0 to %c100 step %c1 iter_args(%acc = %c0_i32) -> (i32) { %val = memref.load %array[%i] : memref<?xi32> %new_acc = arith.addi %acc, %val : i32 scf.yield %new_acc : i32 } // Unsigned comparison scf.for unsigned %i = %lb to %ub step %step : i32 { // loop body }

scf.while - While Loop

Description:While loop with condition check in "before" region and loop body in "after" region.

Syntax:

%result = scf.while (%arg = %init) : (type) -> type { // before region: condition check %condition = ... scf.condition(%condition) %arg : type } do { ^bb0(%arg: type): // after region: loop body %next = ... scf.yield %next : type }

Regions:

• before: Condition check region (terminates withscf.condition)
• after: Loop body region (terminates withscf.yield)

Example:

%result = scf.while (%arg = %init) : (i32) -> i32 { %condition = arith.cmpi slt, %arg, %limit : i32 scf.condition(%condition) %arg : i32 } do { ^bb0(%arg: i32): %next = arith.addi %arg, %c1 : i32 scf.yield %next : i32 }

Conditional Operations

scf.if - If-Then-Else

Description:Conditional branch with optional else block and optional results.

Syntax:

scf.if %condition { // then block } scf.if %condition { // then block } else { // else block } %result = scf.if %condition -> type { // then block scf.yield %value : type } else { // else block scf.yield %other : type }

Operands:

• condition: Boolean condition (i1)

Results:

• Values yielded from branches (if any)

Example:

// Simple if scf.if %condition { // then block } // If-else scf.if %condition { // then block } else { // else block } // If with results %result = scf.if %condition -> i32 { %value = arith.constant 1 : i32 scf.yield %value : i32 } else { %value = arith.constant 0 : i32 scf.yield %value : i32 }

scf.index_switch - Index Switch

Description:Switch statement based on an index value with multiple cases and a default case.

Syntax:

%result = scf.index_switch %arg -> type case 0 { // case 0 block scf.yield %value0 : type } case 1 { // case 1 block scf.yield %value1 : type } default { // default block scf.yield %default_value : type }

Operands:

• arg: Index value to switch on

Attributes:

• cases: Array of case values

Example:

%result = scf.index_switch %idx -> i32 case 0 { %c0 = arith.constant 10 : i32 scf.yield %c0 : i32 } case 1 { %c1 = arith.constant 20 : i32 scf.yield %c1 : i32 } case 2 { %c2 = arith.constant 30 : i32 scf.yield %c2 : i32 } default { %cd = arith.constant 0 : i32 scf.yield %cd : i32 }

Region Operations

scf.execute_region - Execute Region

Description:Execute a region exactly once. Allows multiple blocks within single-block contexts.

Syntax:

%result = scf.execute_region -> type { // region body (can have multiple blocks) scf.yield %value : type } %result = scf.execute_region -> type no_inline { // region body with no_inline attribute scf.yield %value : type }

Attributes:

• no_inline: Optional flag to prevent inlining

Semantics:Executes the region exactly once. Useful for creating multi-block regions within operations that normally allow only single blocks.

Example:

// Simple execute region %result = scf.execute_region -> i32 { %x = arith.constant 42 : i32 scf.yield %x : i32 } // With multiple blocks %result = scf.execute_region -> i32 { cf.cond_br %cond, ^bb1, ^bb2 ^bb1: %c1 = arith.constant 1 : i32 cf.br ^bb3(%c1 : i32) ^bb2: %c2 = arith.constant 2 : i32 cf.br ^bb3(%c2 : i32) ^bb3(%arg: i32): scf.yield %arg : i32 } // With no_inline attribute %result = scf.execute_region -> i32 no_inline { %x = arith.constant 42 : i32 scf.yield %x : i32 }

Terminator Operations

scf.yield - Yield Values

Description:Terminates regions within SCF operations and yields values to parent operation.

Syntax:

scf.yield scf.yield %value : type scf.yield %value1, %value2 : type1, type2

Semantics:Used to terminate:

• Loop bodies (scf.for,scf.whileafter region)

• Conditional branches (scf.if)

• Execute regions (scf.execute_region)

• Switch cases (scf.index_switch)

Example:

// Yield single value scf.yield %value : i32 // Yield multiple values scf.yield %a, %b : i32, f32 // Yield no values scf.yield

scf.condition - Loop Continuation Condition

Description:Terminates the "before" region ofscf.while. If condition is true, continues to "after" region; otherwise exits loop.

Syntax:

scf.condition(%condition) %args... : types...

Operands:

• condition: Boolean condition (i1)
• args: Values to pass to "after" region or return from loop

Semantics:

• Ifconditionis true: execute "after" region withargs
• Ifconditionis false: exit loop and returnargs

Example:

// In scf.while before region %keep_going = arith.cmpi slt, %i, %limit : i32 scf.condition(%keep_going) %i : i32 // With multiple values %cond = arith.cmpi slt, %i, %limit : i32 scf.condition(%cond) %i, %sum : i32, i32

Common Patterns

Pattern 1: Simple Loop

scf.for %i = %c0 to %c100 step %c1 { // loop body }

Pattern 2: Loop with Accumulator

%sum = scf.for %i = %c0 to %c100 step %c1 iter_args(%acc = %c0) -> (i32) { %val = memref.load %array[%i] : memref<?xi32> %new_acc = arith.addi %acc, %val : i32 scf.yield %new_acc : i32 }

Pattern 3: Conditional with Results

%result = scf.if %cond -> i32 { scf.yield %true_val : i32 } else { scf.yield %false_val : i32 }

Pattern 4: While Loop

%final = scf.while (%arg = %init) : (i32) -> i32 { %keep_going = arith.cmpi slt, %arg, %limit : i32 scf.condition(%keep_going) %arg : i32 } do { ^bb0(%arg: i32): %next = arith.addi %arg, %c1 : i32 scf.yield %next : i32 }

Pattern 5: Nested Loops

scf.for %i = %c0 to %M step %c1 { scf.for %j = %c0 to %N step %c1 { // nested loop body } }

Pattern 6: Loop with Multiple Accumulators

%sum, %prod = scf.for %i = %c0 to %c100 step %c1 iter_args(%acc_sum = %c0, %acc_prod = %c1) -> (i32, i32) { %val = memref.load %array[%i] : memref<?xi32> %new_sum = arith.addi %acc_sum, %val : i32 %new_prod = arith.muli %acc_prod, %val : i32 scf.yield %new_sum, %new_prod : i32, i32 }

【免费下载链接】pto-isaParallel Tile Operation (PTO) is a virtual instruction set architecture designed by Ascend CANN, focusing on tile-level operations. This repository offers high-performance, cross-platform tile operations across Ascend platforms.项目地址: https://gitcode.com/cann/pto-isa