Different behaviour on lexicographical reordering of blocks

[vaivaswatha]

This MLIR code fails to compile,

func.func @multiply(%A: i64) -> i64  {
    %B = arith.addi %A, %A : i64
    %Zero = arith.constant 0 : i64
    %C = arith.cmpi eq, %B, %Zero : i64
    %C1 = arith.constant 1 : i1
    cf.cond_br %C, ^bb1, ^bb2

    ^bb1:
        %One = arith.constant 1 : i64
        cf.br ^bb3

    ^bb3:
        %Res = scf.if %C1 -> i64 {
            %Two = arith.constant 2 : i64
            %res = arith.addi %Two, %Two : i64
            scf.yield %res : i64
        } else {
            %One = arith.constant 3 : i64
            %res = arith.addi %One, %One : i64
            scf.yield %res : i64
        }
        return %Res: i64

    ^bb2:
        return %B: i64
}

with error:

$ mlir-opt test.mlir  
test.mlir:18:13: error: redefinition of SSA value '%One'
            %One = arith.constant 3 : i64
            ^
test.mlir:9:9: note: previously defined here
        %One = arith.constant 1 : i64
        ^

However if I move ^bb1 to be lexicographically after ^bb3, the redefinition is no longer detected, and hence no error thrown.

For clarity, this code compiles without errors:

func.func @multiply(%A: i64) -> i64  {
    %B = arith.addi %A, %A : i64
    %Zero = arith.constant 0 : i64
    %C = arith.cmpi eq, %B, %Zero : i64
    %C1 = arith.constant 1 : i1
    cf.cond_br %C, ^bb1, ^bb2

    ^bb3:
        %Res = scf.if %C1 -> i64 {
            %Two = arith.constant 2 : i64
            %res = arith.addi %Two, %Two : i64
            scf.yield %res : i64
        } else {
            %One = arith.constant 3 : i64
            %res = arith.addi %One, %One : i64
            scf.yield %res : i64
        }
        return %Res: i64

    ^bb1:
        %One = arith.constant 1 : i64
    cf.br ^bb3

    ^bb2:
        return %B: i64
}

[llvmbot]

@llvm/issue-subscribers-mlir-core

Author: Vaivaswatha N (vaivaswatha)

This MLIR code fails to compile, ``` func.func @multiply(%A: i64) -> i64 { %B = arith.addi %A, %A : i64 %Zero = arith.constant 0 : i64 %C = arith.cmpi eq, %B, %Zero : i64 %C1 = arith.constant 1 : i1 cf.cond_br %C, ^bb1, ^bb2 ^bb1: %One = arith.constant 1 : i64 cf.br ^bb3 ^bb3: %Res = scf.if %C1 -> i64 { %Two = arith.constant 2 : i64 %res = arith.addi %Two, %Two : i64 scf.yield %res : i64 } else { %One = arith.constant 3 : i64 %res = arith.addi %One, %One : i64 scf.yield %res : i64 } return %Res: i64 ^bb2: return %B: i64 } ``` with error: ``` $ mlir-opt test.mlir test.mlir:18:13: error: redefinition of SSA value '%One' %One = arith.constant 3 : i64 ^ test.mlir:9:9: note: previously defined here %One = arith.constant 1 : i64 ^ ``` However if I move `^bb1` to be lexicographically after `^bb3`, the redefinition is no longer detected, and hence no error thrown. For clarity, this code compiles without errors: ``` func.func @multiply(%A: i64) -> i64 { %B = arith.addi %A, %A : i64 %Zero = arith.constant 0 : i64 %C = arith.cmpi eq, %B, %Zero : i64 %C1 = arith.constant 1 : i1 cf.cond_br %C, ^bb1, ^bb2 ^bb3: %Res = scf.if %C1 -> i64 { %Two = arith.constant 2 : i64 %res = arith.addi %Two, %Two : i64 scf.yield %res : i64 } else { %One = arith.constant 3 : i64 %res = arith.addi %One, %One : i64 scf.yield %res : i64 } return %Res: i64 ^bb1: %One = arith.constant 1 : i64 cf.br ^bb3 ^bb2: return %B: i64 } ```

[llvmbot]

@llvm/issue-subscribers-bug

Author: Vaivaswatha N (vaivaswatha)

This MLIR code fails to compile, ``` func.func @multiply(%A: i64) -> i64 { %B = arith.addi %A, %A : i64 %Zero = arith.constant 0 : i64 %C = arith.cmpi eq, %B, %Zero : i64 %C1 = arith.constant 1 : i1 cf.cond_br %C, ^bb1, ^bb2 ^bb1: %One = arith.constant 1 : i64 cf.br ^bb3 ^bb3: %Res = scf.if %C1 -> i64 { %Two = arith.constant 2 : i64 %res = arith.addi %Two, %Two : i64 scf.yield %res : i64 } else { %One = arith.constant 3 : i64 %res = arith.addi %One, %One : i64 scf.yield %res : i64 } return %Res: i64 ^bb2: return %B: i64 } ``` with error: ``` $ mlir-opt test.mlir test.mlir:18:13: error: redefinition of SSA value '%One' %One = arith.constant 3 : i64 ^ test.mlir:9:9: note: previously defined here %One = arith.constant 1 : i64 ^ ``` However if I move `^bb1` to be lexicographically after `^bb3`, the redefinition is no longer detected, and hence no error thrown. For clarity, this code compiles without errors: ``` func.func @multiply(%A: i64) -> i64 { %B = arith.addi %A, %A : i64 %Zero = arith.constant 0 : i64 %C = arith.cmpi eq, %B, %Zero : i64 %C1 = arith.constant 1 : i1 cf.cond_br %C, ^bb1, ^bb2 ^bb3: %Res = scf.if %C1 -> i64 { %Two = arith.constant 2 : i64 %res = arith.addi %Two, %Two : i64 scf.yield %res : i64 } else { %One = arith.constant 3 : i64 %res = arith.addi %One, %One : i64 scf.yield %res : i64 } return %Res: i64 ^bb1: %One = arith.constant 1 : i64 cf.br ^bb3 ^bb2: return %B: i64 } ```