[PATCH] D159275: libclc: Fix signed interger underflow in abs_diff

[Fraser Cormack via Phabricator via llvm-commits]

frasercrmck created this revision.
frasercrmck added reviewers: kpet, rjodinchr, aarongreig.
Herald added subscribers: jvesely, Anastasia.
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frasercrmck requested review of this revision.
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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.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D159275

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


Index: libclc/generic/lib/integer/abs_diff.inc
===================================================================
--- libclc/generic/lib/integer/abs_diff.inc
+++ 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;
 }


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