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[mlir][SCF] Do not verify step size of scf.for (#78141)

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An op verifier should verify only local properties. This commit removes
the verification of `scf.for` step sizes. (Verifiers can check
attributes but should not follow SSA values.) This verification could
reject IR that is actually valid, e.g.:

```mlir
scf.if %always_false {
  // Branch is never entered.
  scf.for ... step %c0 { ... }
}
```

This commit fixes `for-loop-peeling.mlir` when running with
`MLIR_ENABLE_EXPENSIVE_PATTERN_API_CHECKS`:
```
within split at llvm-project/mlir/test/Dialect/SCF/for-loop-peeling.mlir:293 offset :9:3: note: see current operation:
"scf.for"(%0, %3, %2) ({
^bb0(%arg1: index):
  %4 = "arith.index_cast"(%arg1) : (index) -> i64
  "memref.store"(%4, %arg0) : (i64, memref<i64>) -> ()
  "scf.yield"() : () -> ()
}) {__peeled_loop__} : (index, index, index) -> ()
LLVM ERROR: IR failed to verify after folding
```

Note: `%2` is `arith.constant 0 : index`.
This commit is contained in:
Matthias Springer 2024-01-15 17:46:54 +01:00 committed by GitHub
parent fcfe1b6482
commit c1730f4221
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GPG Key ID: 4AEE18F83AFDEB23
3 changed files with 6 additions and 18 deletions
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4
mlir/lib/Dialect/SCF/IR/SCF.cpp
View File

@ -332,10 +332,6 @@ void ForOp::build(OpBuilder &builder, OperationState &result, Value lb,
}
LogicalResult ForOp::verify() {
IntegerAttr step;
if (matchPattern(getStep(), m_Constant(&step)) && step.getInt() <= 0)
return emitOpError("constant step operand must be positive");
// Check that the number of init args and op results is the same.
if (getInitArgs().size() != getNumResults())
return emitOpError(

8
mlir/test/Dialect/SCF/for-loop-peeling.mlir
View File

@ -292,15 +292,19 @@ func.func @regression(%arg0: memref<i64>, %arg1: index) {
// -----
// Check that this doesn't crash but trigger the verifier.
// Regression test: Make sure that we do not crash.
// CHECK-LABEL: func @zero_step(
// CHECK: scf.for
// CHECK: scf.for
func.func @zero_step(%arg0: memref<i64>) {
%c0 = arith.constant 0 : index
%c1 = arith.constant 1 : index
%foldto0 = arith.subi %c1, %c1 : index
// expected-error @+1 {{'scf.for' op constant step operand must be positive}}
scf.for %arg2 = %c0 to %c1 step %foldto0 {
%2 = arith.index_cast %arg2 : index to i64
memref.store %2, %arg0[] : memref<i64>
}
return
}

12
mlir/test/Dialect/SCF/invalid.mlir
View File

@ -32,18 +32,6 @@ func.func @loop_for_mismatch(%arg0: i32, %arg1: index) {
// -----
func.func @loop_for_step_positive(%arg0: index) {
// expected-error@+2 {{constant step operand must be positive}}
%c0 = arith.constant 0 : index
"scf.for"(%arg0, %arg0, %c0) ({
^bb0(%arg1: index):
scf.yield
}) : (index, index, index) -> ()
return
}
// -----
func.func @loop_for_one_region(%arg0: index) {
// expected-error@+1 {{requires one region}}
"scf.for"(%arg0, %arg0, %arg0) (