Sign extension not properly propagated to users

[j2kun]

Given the following C++ code:

short isqrt(short num) {
  short res = 0;
  short bit = 1 << 14;  // ((unsigned) INT16_MAX + 1) / 2.

  for (int i = 0; i < 8; ++i) {
    if (num >= res + bit) {
      num -= res + bit;
      res = (res >> 1) + bit;
    } else {
      res >>= 1;
    }
    bit >>= 2;
  }
  return res;
}

Running cgeist at 4b04755 as follows:

bin/cgeist \
  '-function=*' \
  -raise-scf-to-affine \
  --memref-fullrank \
  -S \
  -O0 \
  sqrt.cc

Produces

loc("/path/to/sqrt.cc":25:11): error: 'arith.subi' op requires the same type for all operands and results
"builtin.module"() ({
  "func.func"() <{function_type = (i16) -> i16, sym_name = "_Z5isqrts"}> ({
  ^bb0(%arg0: i16):
    %0 = "arith.constant"() <{value = 16384 : i16}> : () -> i16
    %1 = "arith.constant"() <{value = 2 : i16}> : () -> i16
    %2 = "arith.constant"() <{value = 1 : i16}> : () -> i16
    %3 = "arith.constant"() <{value = 1 : i32}> : () -> i32
    %4 = "arith.constant"() <{value = 0 : i16}> : () -> i16
    %5:3 = "affine.for"(%0, %4, %arg0) ({
    ^bb0(%arg1: index, %arg2: i16, %arg3: i16, %arg4: i16):
      %6 = "arith.extsi"(%arg4) : (i16) -> i32
      %7 = "arith.extsi"(%arg3) : (i16) -> i32
      %8 = "arith.extsi"(%arg2) : (i16) -> i32
      %9 = "arith.addi"(%7, %8) : (i32, i32) -> i32
      %10 = "arith.cmpi"(%6, %9) <{predicate = 5 : i64}> : (i32, i32) -> i1
      %11:2 = "scf.if"(%10) ({
        %13 = "arith.subi"(%arg4, %9) : (i16, i32) -> i16
        %14 = "arith.shrsi"(%7, %3) : (i32, i32) -> i32
        %15 = "arith.addi"(%14, %8) : (i32, i32) -> i32
        %16 = "arith.trunci"(%15) : (i32) -> i16
        "scf.yield"(%16, %13) : (i16, i16) -> ()
      }, {
        %13 = "arith.shrsi"(%arg3, %2) : (i16, i16) -> i16
        "scf.yield"(%13, %arg4) : (i16, i16) -> ()
      }) : (i1) -> (i16, i16)
      %12 = "arith.shrsi"(%arg2, %1) : (i16, i16) -> i16
      "affine.yield"(%12, %11#0, %11#1) : (i16, i16, i16) -> ()
    }) {lower_bound = affine_map<() -> (0)>, step = 1 : index, upper_bound = affine_map<() -> (8)>} : (i16, i16, i16) -> (i16, i16, i16)
    "func.return"(%5#1) : (i16) -> ()
  }) {llvm.linkage = #llvm.linkage<external>} : () -> ()
}) {<lots of attributes>} : () -> ()

It looks like the issue is that

%13 = "arith.subi"(%arg4, %9) : (i16, i32) -> i16

Is still using %arg4 even though it was sign extended in an earlier line

%6 = "arith.extsi"(%arg4) : (i16) -> i32

[j2kun]

@ivanradanov I'd like to fix this issue along with #388. Is the project actively soliciting contributions? Is there bandwidth to review my fixes? It's not clear to me who is the official maintainer to contact, so please redirect me if it's not you.

[wsmoses]

Go for it patches welcome!