Subzero: Make sure alloca with align=0 is handled correctly.

src/IceTargetLoweringX8632.cpp

Index: src/IceTargetLoweringX8632.cpp
diff --git a/src/IceTargetLoweringX8632.cpp b/src/IceTargetLoweringX8632.cpp
index 756508ec4d7ccc17dc011d67a86bbb0cb2c50e2c..c3a6e4d33fb247a6e882d1cc787bb9a4a9db78a7 100644
--- a/src/IceTargetLoweringX8632.cpp
+++ b/src/IceTargetLoweringX8632.cpp
@@ -1118,6 +1118,9 @@ void TargetX8632::lowerAlloca(const InstAlloca *Inst) {
   Operand *TotalSize = legalize(Inst->getSizeInBytes());
   Variable *Dest = Inst->getDest();
   uint32_t AlignmentParam = Inst->getAlignInBytes();
+  // For default align=0, set it to the real value 1, to avoid any
+  // bit-manipulation problems below.
+  AlignmentParam = std::max(AlignmentParam, 1u);
 
   // LLVM enforces power of 2 alignment.
   assert((AlignmentParam & (AlignmentParam - 1)) == 0);