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[MLIR] Erase unreachable blocks before applying patterns in the greedy rewriter (#153957)

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Operations like:

    %add = arith.addi %add, %add : i64

are legal in unreachable code. Unfortunately many patterns would be
unsafe to apply on such IR and can lead to crashes or infinite loops. To
avoid this we can remove unreachable blocks before attempting to apply
patterns.
We may have to do this also whenever the CFG is changed by a pattern, it
is left up for future work right now.

Fixes #153732
This commit is contained in:
Mehdi Amini 2025-08-18 10:59:43 +02:00 committed by GitHub
parent 7ee6cf06c8
commit 87e6fd161a
No known key found for this signature in database
GPG Key ID: B5690EEEBB952194
3 changed files with 34 additions and 10 deletions
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13
mlir/lib/Transforms/Utils/GreedyPatternRewriteDriver.cpp
View File

@ -871,7 +871,18 @@ LogicalResult RegionPatternRewriteDriver::simplify(bool *changed) && {
ctx->executeAction<GreedyPatternRewriteIteration>(
[&] {
continueRewrites = processWorklist();
continueRewrites = false;
// Erase unreachable blocks
// Operations like:
// %add = arith.addi %add, %add : i64
// are legal in unreachable code. Unfortunately many patterns would be
// unsafe to apply on such IR and can lead to crashes or infinite
// loops.
continueRewrites |=
succeeded(eraseUnreachableBlocks(rewriter, region));
continueRewrites |= processWorklist();
// After applying patterns, make sure that the CFG of each of the
// regions is kept up to date.

15
mlir/test/Dialect/Arith/canonicalize.mlir
View File

@ -3363,3 +3363,18 @@ func.func @bf16_fma(%arg0: vector<32x32x32xbf16>, %arg1: vector<32x32x32xbf16>,
}
}
#-}
// CHECK-LABEL: func @unreachable()
// CHECK-NEXT: return
// CHECK-NOT: arith
func.func @unreachable() {
return
^unreachable:
%c1_i64 = arith.constant 1 : i64
// This self referencing operation is legal in an unreachable block.
// Many patterns are unsafe with respect to this kind of situation,
// check that we don't infinite loop here.
%add = arith.addi %add, %c1_i64 : i64
cf.br ^unreachable
}

16
mlir/test/Transforms/test-canonicalize.mlir
View File

@ -1,4 +1,4 @@
// RUN: mlir-opt %s -pass-pipeline='builtin.module(func.func(canonicalize))' | FileCheck %s
// RUN: mlir-opt %s -pass-pipeline='builtin.module(func.func(canonicalize))' | FileCheck %s --check-prefixes=CHECK,RS
// RUN: mlir-opt %s -pass-pipeline='builtin.module(func.func(canonicalize{region-simplify=disabled}))' | FileCheck %s --check-prefixes=CHECK,NO-RS
// CHECK-LABEL: func @remove_op_with_inner_ops_pattern
@ -80,12 +80,10 @@ func.func @test_dialect_canonicalizer() -> (i32) {
// Check that the option to control region simplification actually works
// CHECK-LABEL: test_region_simplify
func.func @test_region_simplify() {
// CHECK-NEXT: return
// NO-RS-NEXT: ^bb1
// NO-RS-NEXT: return
// CHECK-NEXT: }
return
^bb1:
return
func.func @test_region_simplify(%input1 : i32, %cond : i1) -> i32 {
// RS-NEXT: "test.br"(%arg0)[^bb1] : (i32) -> ()
// NO-RS-NEXT: "test.br"(%arg0, %arg0)[^bb1] : (i32, i32) -> ()
"test.br"(%input1, %input1)[^bb1] : (i32, i32) -> ()
^bb1(%used_arg : i32, %unused_arg : i32):
return %used_arg : i32
}