Handle constant sized array allocations using no extension (#2713)

In LLVM, array allocations might have constant size:

%array = alloca i32, i64 4, align 4
Represent this kind of allocations using OpVariable + OpBitcast.

Before this patch, the SPV_INTEL_variable_length_array extension was used.

Signed-off-by: Victor Perez <[email protected]>

Original commit:
KhronosGroup/SPIRV-LLVM-Translator@ea2fcc172f6861e

Author: victor-eds

llvm-spirv/lib/SPIRV/SPIRVWriter.cpp

@@ -2268,14 +2268,14 @@ LLVMToSPIRVBase::transValueWithoutDecoration(Value *V, SPIRVBasicBlock *BB,
       SPIRVValue *Length = transValue(Alc->getArraySize(), BB);
       assert(Length && "Couldn't translate array size!");
 
-      if (isSpecConstantOpCode(Length->getOpCode())) {
-        // SPIR-V arrays length can be expressed using a specialization
-        // constant.
+      if (isConstantOpCode(Length->getOpCode())) {
+        // Length can be any constant instruction, either a specialization
+        // constant or a non-specialization constant.
         //
-        // Spec Constant Length Arrays need special treatment, as the allocation
-        // type will be 'OpTypePointer(Function, OpTypeArray(ElementType,
-        // Length))', we need to bitcast the obtained pointer to the expected
-        // type: 'OpTypePointer(Function, ElementType).
+        // Array allocations need special treatment: as the allocation type will
+        // be 'OpTypePointer(Function, OpTypeArray(ElementType, Length))', we
+        // need to bitcast the obtained pointer to the expected type:
+        // 'OpTypePointer(Function, ElementType).
         SPIRVType *AllocationType = BM->addPointerType(
             StorageClassFunction,
             BM->addArrayType(transType(Alc->getAllocatedType()), Length));

llvm-spirv/test/array-alloca.ll

@@ -0,0 +1,52 @@
+; RUN: llvm-as %s -o %t.bc
+; RUN: llvm-spirv %t.bc -o %t.spv
+
+; Validation test.
+; RUN: spirv-val %t.spv
+
+; SPIR-V codegen test.
+; RUN: llvm-spirv %t.bc -spirv-text -o - | FileCheck %s --check-prefix=CHECK-SPIRV
+
+; Roundtrip test.
+; RUN: llvm-spirv -r %t.spv -o - | llvm-dis -o - | FileCheck %s --check-prefix=CHECK-LLVM
+
+target datalayout = "e-i64:64-v16:16-v24:32-v32:32-v48:64-v96:128-v192:256-v256:256-v512:512-v1024:1024"
+target triple = "spir64-unknown-unknown"
+
+; CHECK-SPIRV: Decorate [[#ARR:]] Alignment 4
+; CHECK-SPIRV: Decorate [[#BITARR:]] Alignment 4
+
+; CHECK-SPIRV: TypeInt [[#I32:]] 32 0
+; CHECK-SPIRV: TypeInt [[#I64:]] 64 0
+; CHECK-SPIRV: Constant [[#I64]] [[#SIZE:]] 4 0
+; CHECK-SPIRV: TypeVoid [[#VOID:]]
+; CHECK-SPIRV: TypeFunction [[#FUNCTY:]] [[#VOID]]
+; CHECK-SPIRV: TypePointer [[#PTRTY:]] [[#FUNCSTORAGE:]] [[#I32]]
+; CHECK-SPIRV: TypeArray [[#ARRTY:]] [[#I32]] [[#SIZE]]
+; CHECK-SPIRV: TypePointer [[#ARRPTRTY:]] [[#FUNCSTORAGE]] [[#ARRTY]]
+
+; CHECK-SPIRV: Function [[#VOID]] {{.*}} [[#FUNCTY]]
+; CHECK-SPIRV: Variable [[#ARRPTRTY]] [[#ARR]] [[#FUNCSTORAGE]]
+; CHECK-SPIRV: Bitcast [[#PTRTY]] [[#BITARR]] [[#ARR]]
+
+; Generated LLVM is different, but equivalent as an array type is allocated.
+; CHECK-LLVM:  define spir_func void @test_array_alloca()
+; CHECK-LLVM:    %[[#ALLOC:]] = alloca [4 x i32], align 4
+; CHECK-LLVM:    %{{.*}} = bitcast ptr %[[#ALLOC]] to ptr
+define dso_local void @test_array_alloca() #0 {
+  %arr = alloca i32, i64 4, align 4
+  ret void
+}
+
+attributes #0 = { nounwind "less-precise-fpmad"="false" "no-frame-pointer-elim"="false" "no-infs-fp-math"="false" "no-nans-fp-math"="false" "no-realign-stack" "stack-protector-buffer-size"="8" "unsafe-fp-math"="false" "use-soft-float"="false" }
+
+!opencl.enable.FP_CONTRACT = !{}
+!opencl.spir.version = !{!1}
+!opencl.ocl.version = !{!1}
+!opencl.used.extensions = !{!2}
+!opencl.used.optional.core.features = !{!3}
+!opencl.compiler.options = !{!2}
+
+!1 = !{i32 1, i32 2}
+!2 = !{}
+!3 = !{}