[libclc] 37a3de1 - libclc: Fix signed integer underflow in abs_diff

[Fraser Cormack via cfe-commits]

Author: Fraser Cormack
Date: 2023-08-31T14:28:16+01:00
New Revision: 37a3de1e2eedf848b8442217ef3790436f69a7db

URL: https://github.com/llvm/llvm-project/commit/37a3de1e2eedf848b8442217ef3790436f69a7db
DIFF: https://github.com/llvm/llvm-project/commit/37a3de1e2eedf848b8442217ef3790436f69a7db.diff

LOG: libclc: Fix signed integer underflow in abs_diff

We noticed this same issue in our own implementation of abs_diff, and
the same issue also came up in the abs_diff reference function in the
OpenCL CTS.

Reviewed By: rjodinchr

Differential Revision: https://reviews.llvm.org/D159275

Added: 
    

Modified: 
    libclc/generic/lib/integer/abs_diff.inc

Removed: 
    


################################################################################
diff  --git a/libclc/generic/lib/integer/abs_
diff .inc b/libclc/generic/lib/integer/abs_
diff .inc
index f39c3ff4d3e8ab..2d3c492cae0e68 100644
--- a/libclc/generic/lib/integer/abs_
diff .inc
+++ b/libclc/generic/lib/integer/abs_
diff .inc
@@ -1,3 +1,5 @@
 _CLC_OVERLOAD _CLC_DEF __CLC_U_GENTYPE abs_
diff (__CLC_GENTYPE x, __CLC_GENTYPE y) {
-  return __builtin_astype((__CLC_GENTYPE)(x > y ? x-y : y-x), __CLC_U_GENTYPE);
+  __CLC_U_GENTYPE ux = __builtin_astype(x, __CLC_U_GENTYPE);
+  __CLC_U_GENTYPE uy = __builtin_astype(y, __CLC_U_GENTYPE);
+  return x > y ? ux - uy : uy - ux;
 }