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[mlir][scf]: Add value bound between scf for loop yield and result #123200

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Jan 19, 2025
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[mlir][scf]: Add value bound between scf for loop yield and result #123200

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16 changes: 16 additions & 0 deletions mlir/lib/Dialect/SCF/IR/ValueBoundsOpInterfaceImpl.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -70,6 +70,22 @@ struct ForOpInterface
cstr.bound(value) == cstr.getExpr(initArg);
}
}

if (dim.has_value() || isa<BlockArgument>(value))
return;

// `value` is result of `forOp`, we can prove that:
// %result == %init_arg + trip_count * (%yielded_value - %iter_arg).
// Where trip_count is (ub - lb) / step.
AffineExpr lbExpr = cstr.getExpr(forOp.getLowerBound());
AffineExpr ubExpr = cstr.getExpr(forOp.getUpperBound());
AffineExpr stepExpr = cstr.getExpr(forOp.getStep());
AffineExpr tripCountExpr =
AffineExpr(ubExpr - lbExpr).ceilDiv(stepExpr); // (ub - lb) / step
AffineExpr oneIterAdvanceExpr =
cstr.getExpr(yieldedValue) - cstr.getExpr(iterArg);
cstr.bound(value) ==
cstr.getExpr(initArg) + AffineExpr(tripCountExpr * oneIterAdvanceExpr);
}

void populateBoundsForIndexValue(Operation *op, Value value,
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71 changes: 71 additions & 0 deletions mlir/test/Dialect/SCF/value-bounds-op-interface-impl.mlir
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Expand Up @@ -267,3 +267,74 @@ func.func @compare_scf_for(%a: index, %b: index, %c: index) {
}
return
}

// -----

func.func @scf_for_result_infer() {
%c0 = arith.constant 0 : index
%c1 = arith.constant 1 : index
%c10 = arith.constant 10 : index
%0 = scf.for %iv = %c0 to %c10 step %c1 iter_args(%arg = %c0) -> index {
%2 = "test.some_use"() : () -> (i1)
%3 = scf.if %2 -> (index) {
%5 = arith.addi %arg, %c1 : index
scf.yield %5 : index
} else {
scf.yield %arg : index
}
scf.yield %3 : index
}
// expected-remark @below{{true}}
"test.compare"(%0, %c10) {cmp = "LE"} : (index, index) -> ()
return
}

// -----

func.func @scf_for_result_infer_dynamic_init(%i : index) {
%c0 = arith.constant 0 : index
%c1 = arith.constant 1 : index
%c10 = arith.constant 10 : index
%0 = scf.for %iv = %c0 to %c10 step %c1 iter_args(%arg = %i) -> index {
%2 = "test.some_use"() : () -> (i1)
%3 = scf.if %2 -> (index) {
%5 = arith.addi %arg, %c1 : index
scf.yield %5 : index
} else {
scf.yield %arg : index
}
scf.yield %3 : index
}
%6 = arith.addi %i, %c10 : index
// expected-remark @below{{true}}
"test.compare"(%0, %6) {cmp = "LE"} : (index, index) -> ()
return
}

// -----

func.func @scf_for_result_infer_dynamic_init_big_step(%i : index) {
%c0 = arith.constant 0 : index
%c1 = arith.constant 1 : index
%c2 = arith.constant 2 : index
%c4 = arith.constant 4 : index
%c5 = arith.constant 5 : index
%c10 = arith.constant 10 : index
%0 = scf.for %iv = %c0 to %c10 step %c2 iter_args(%arg = %i) -> index {
%2 = "test.some_use"() : () -> (i1)
%3 = scf.if %2 -> (index) {
%5 = arith.addi %arg, %c1 : index
scf.yield %5 : index
} else {
scf.yield %arg : index
}
scf.yield %3 : index
}
%6 = arith.addi %i, %c5 : index
%7 = arith.addi %i, %c4 : index
// expected-remark @below{{true}}
"test.compare"(%0, %6) {cmp = "LE"} : (index, index) -> ()
// expected-error @below{{unknown}}
"test.compare"(%0, %7) {cmp = "LE"} : (index, index) -> ()
return
}
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