[Polly] [ScheduleOptimizer] Prevent incorrect tile size computation

Because Polly exposes parameters that directly influence tile size
calculations, one can setup situations like divide-by-zero.

Check against a possible divide-by-zero in getMacroKernelParams
and return early.

Also assert at the end of getMacroKernelParams that the block sizes
computed for matrices are positive (>= 1).

Tags: #polly

Differential Revision: https://reviews.llvm.org/D31708

llvm-svn: 299633

1 files changed, 11 insertions, 0 deletions

diff --git a/polly/lib/Transform/ScheduleOptimizer.cpp b/polly/lib/Transform/ScheduleOptimizer.cpp
index 83c97d12641..ba1373e7be2 100644
--- a/polly/lib/Transform/ScheduleOptimizer.cpp
+++ b/polly/lib/Transform/ScheduleOptimizer.cpp
@@ -1014,6 +1014,14 @@ getMacroKernelParams(const MicroKernelParamsTy &MicroKernelParams,
   int Car = floor(
       (FirstCacheLevelAssociativity - 1) /
       (1 + static_cast<double>(MicroKernelParams.Nr) / MicroKernelParams.Mr));
+
+  // Car can be computed to be zero since it is floor to int.
+  // On Mac OS, division by 0 does not raise a signal. This causes negative
+  // tile sizes to be computed. Prevent division by 0 Cac by early returning
+  // if this happens.
+  if (Car == 0)
+    return {1, 1, 1};
+
   auto ElementSize = getMatMulAlignTypeSize(MMI);
   assert(ElementSize > 0 && "The element size of the matrix multiplication "
                             "operands should be greater than zero.");
@@ -1024,6 +1032,9 @@ getMacroKernelParams(const MicroKernelParamsTy &MicroKernelParams,
       SecondCacheLevelSize;
   int Mc = floor((SecondCacheLevelAssociativity - 2) / Cac);
   int Nc = PollyPatternMatchingNcQuotient * MicroKernelParams.Nr;
+
+  assert(Mc > 0 && Nc > 0 && Kc > 0 &&
+         "Matrix block sizes should be  greater than zero");
   return {Mc, Nc, Kc};
 }