[clang codegen] Clean up handling of vectors with trivial-auto-var-init.

The code was pretending to be doing something useful with vectors, but
really it was doing nothing: the element type of a vector is always a
scalar type, so constWithPadding would always just return the input constant.

Split off from D75661 so it can be reviewed separately.

While I'm here, also add testcase to show missing vector handling.

Differential Revision: https://reviews.llvm.org/D76528

clang/lib/CodeGen/CGDecl.cpp

@@ -1050,13 +1050,13 @@ static llvm::Constant *constWithPadding(CodeGenModule &CGM, IsPattern isPattern,
   llvm::Type *OrigTy = constant->getType();
   if (const auto STy = dyn_cast<llvm::StructType>(OrigTy))
     return constStructWithPadding(CGM, isPattern, STy, constant);
-  if (auto *STy = dyn_cast<llvm::SequentialType>(OrigTy)) {
+  if (auto *ArrayTy = dyn_cast<llvm::ArrayType>(OrigTy)) {
     llvm::SmallVector<llvm::Constant *, 8> Values;
-    unsigned Size = STy->getNumElements();
+    uint64_t Size = ArrayTy->getNumElements();
     if (!Size)
       return constant;
-    llvm::Type *ElemTy = STy->getElementType();
-    bool ZeroInitializer = constant->isZeroValue();
+    llvm::Type *ElemTy = ArrayTy->getElementType();
+    bool ZeroInitializer = constant->isNullValue();
     llvm::Constant *OpValue, *PaddedOp;
     if (ZeroInitializer) {
       OpValue = llvm::Constant::getNullValue(ElemTy);
@@ -1072,13 +1072,10 @@ static llvm::Constant *constWithPadding(CodeGenModule &CGM, IsPattern isPattern,
     auto *NewElemTy = Values[0]->getType();
     if (NewElemTy == ElemTy)
       return constant;
-    if (OrigTy->isArrayTy()) {
-      auto *ArrayTy = llvm::ArrayType::get(NewElemTy, Size);
-      return llvm::ConstantArray::get(ArrayTy, Values);
-    } else {
-      return llvm::ConstantVector::get(Values);
-    }
+    auto *NewArrayTy = llvm::ArrayType::get(NewElemTy, Size);
+    return llvm::ConstantArray::get(NewArrayTy, Values);
   }
+  // FIXME: Do we need to handle tail padding in vectors?
   return constant;
 }
 

clang/test/CodeGenCXX/auto-var-init.cpp

@@ -1610,5 +1610,24 @@ TEST_CUSTOM(doublevec32, double  __attribute__((vector_size(32))), { 3.141592653
 // CHECK-NEXT:  store <4 x double> <double 0x400921FB54442D18, double 0x400921FB54442D18, double 0x400921FB54442D18, double 0x400921FB54442D18>, <4 x double>* %custom, align [[ALIGN]]
 // CHECK-NEXT:  call void @{{.*}}used{{.*}}%custom)
 
+// TODO: This vector has tail padding
+TEST_UNINIT(doublevec24, double  __attribute__((vector_size(24))));
+// CHECK-LABEL: @test_doublevec24_uninit()
+// CHECK:       %uninit = alloca <3 x double>, align
+// CHECK-NEXT:  call void @{{.*}}used{{.*}}%uninit)
+// PATTERN-LABEL: @test_doublevec24_uninit()
+// PATTERN: store <3 x double> <double 0xFFFFFFFFFFFFFFFF, double 0xFFFFFFFFFFFFFFFF, double 0xFFFFFFFFFFFFFFFF>, <3 x double>* %uninit, align 32
+// ZERO-LABEL: @test_doublevec24_uninit()
+// ZERO: store <3 x double> zeroinitializer, <3 x double>* %uninit, align 32
+
+// TODO: This vector has tail padding
+TEST_UNINIT(longdoublevec32, long double  __attribute__((vector_size(sizeof(long double)*2))));
+// CHECK-LABEL: @test_longdoublevec32_uninit()
+// CHECK:       %uninit = alloca <2 x x86_fp80>, align
+// CHECK-NEXT:  call void @{{.*}}used{{.*}}%uninit)
+// PATTERN-LABEL: @test_longdoublevec32_uninit()
+// PATTERN: store <2 x x86_fp80> <x86_fp80 0xKFFFFFFFFFFFFFFFFFFFF, x86_fp80 0xKFFFFFFFFFFFFFFFFFFFF>, <2 x x86_fp80>* %uninit, align 32
+// ZERO-LABEL: @test_longdoublevec32_uninit()
+// ZERO: store <2 x x86_fp80> zeroinitializer, <2 x x86_fp80>* %uninit, align 32
 
 } // extern "C"