W/A GCC maybe-uninitialized warning (#2588)

Signed-off-by: Sidorov, Dmitry <[email protected]>

Original commit:
KhronosGroup/SPIRV-LLVM-Translator@0fd9882186c73e1

Author: MrSidims

llvm-spirv/lib/SPIRV/SPIRVWriter.cpp

@@ -4443,17 +4443,22 @@ SPIRVValue *LLVMToSPIRVBase::transIntrinsicInst(IntrinsicInst *II,
     SPIRVValue *StartingSVal = transValue(II->getArgOperand(0), BB);
     SPIRVTypeInt *I32STy = BM->addIntegerType(32);
     unsigned VecSize = VecTy->getElementCount().getFixedValue();
-    SmallVector<SPIRVValue *, 16> Extracts(VecSize);
-    for (unsigned Idx = 0; Idx < VecSize; ++Idx) {
-      Extracts[Idx] = BM->addVectorExtractDynamicInst(
-          VecSVal, BM->addIntegerConstant(I32STy, Idx), BB);
-    }
-    SPIRVValue *V = BM->addBinaryInst(Op, StartingSVal->getType(), StartingSVal,
-                                      Extracts[0], BB);
-    for (unsigned Idx = 1; Idx < VecSize; ++Idx) {
-      V = BM->addBinaryInst(Op, StartingSVal->getType(), V, Extracts[Idx], BB);
+    if (VecSize > 0) {
+      SmallVector<SPIRVValue *, 16> Extracts(VecSize);
+      for (unsigned Idx = 0; Idx < VecSize; ++Idx) {
+        Extracts[Idx] = BM->addVectorExtractDynamicInst(
+            VecSVal, BM->addIntegerConstant(I32STy, Idx), BB);
+      }
+      SPIRVValue *V = BM->addBinaryInst(Op, StartingSVal->getType(),
+                                        StartingSVal, Extracts[0], BB);
+      for (unsigned Idx = 1; Idx < VecSize; ++Idx) {
+        V = BM->addBinaryInst(Op, StartingSVal->getType(), V, Extracts[Idx],
+                              BB);
+      }
+      return V;
     }
-    return V;
+    assert(VecSize && "Zero Extracts size for vector reduce lowering");
+    return nullptr;
   }
   case Intrinsic::vector_reduce_smax:
   case Intrinsic::vector_reduce_smin: