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

src/IceInst.cpp

@@ -534,7 +534,8 @@ void InstAlloca::dump(const Cfg *Func) const {
   dumpDest(Func);
   Str << " = alloca i8, i32 ";
   getSizeInBytes()->dump(Func);
-  Str << ", align " << getAlignInBytes();
+  if (getAlignInBytes())
+    Str << ", align " << getAlignInBytes();
 }
 
 void InstArithmetic::dump(const Cfg *Func) const {

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);

tests_lit/llvm2ice_tests/alloc.ll

@@ -104,6 +104,19 @@ entry:
 ; CHECK:      mov     dword ptr [esp], eax
 ; CHECK:      call    f2
 
+; Test alloca with default (0) alignment.
+define void @align0(i32 %n) {
+entry:
+  %array = alloca i8, i32 %n
+  %__2 = ptrtoint i8* %array to i32
+  call void @f2(i32 %__2)
+  ret void
+}
+; CHECK-LABEL: align0
+; CHECK: add [[REG:.*]], 15
+; CHECK: and [[REG]], -16
+; CHECK: sub esp, [[REG]]
+
 define void @f2(i32 %ignored) {
 entry:
   ret void