Fix function with unused sret parameter (#2381)

Usually sret parameters are accessed by a memory instruction, from which
would tell SPIRVTypeScavenger which type to use for this function
parameter. But if sret parameter is unused later in the module scavenger
would fail attempting to deduce type from the mangled name.

Signed-off-by: Sidorov, Dmitry <dmitry.sidorov@intel.com>

lib/SPIRV/SPIRVTypeScavenger.cpp

@@ -734,7 +734,8 @@ void SPIRVTypeScavenger::deduceFunctionType(Function &F) {
         for (Argument *Arg : PointerArgs) {
           if (auto *Ty =
                   dyn_cast<TypedPointerType>(ParamTypes[Arg->getArgNo()]))
-            TypeArgument(Arg, Ty);
+            if (!Arg->hasAttribute(Attribute::StructRet))
+              TypeArgument(Arg, Ty);
         }
       }
     }

test/transcoding/unused-sret-opaque-ptr.ll

@@ -0,0 +1,30 @@
+; RUN: llvm-as %s -o %t.bc
+; RUN: llvm-spirv %t.bc -spirv-text -o %t.txt
+; RUN: FileCheck < %t.txt %s --check-prefix=CHECK-SPIRV
+; RUN: llvm-spirv %t.bc -o %t.spv
+; RUN: spirv-val %t.spv
+; RUN: llvm-spirv -r %t.spv -o %t.rev.bc
+; RUN: llvm-dis < %t.rev.bc | FileCheck %s --check-prefix=CHECK-LLVM
+
+; CHECK-SPIRV-DAG: Name [[#Fun:]] "_Z3booi"
+; CHECK-SPIRV-DAG: Decorate [[#Param:]] FuncParamAttr 3
+; CHECK-SPIRV-DAG: TypePointer [[#PtrTy:]] [[#]] [[#StructTy:]]
+; CHECK-SPIRV-DAG: TypeStruct [[#StructTy]]
+; CHECK-SPIRV: Function [[#]] [[#Fun]]
+; CHECK-SPIRV: FunctionParameter [[#PtrTy:]] [[#Param]]
+
+; CHECK-LLVM: call spir_func void @_Z3booi(ptr sret(%struct.Example) align 8
+
+source_filename = "/app/example.cpp"
+target datalayout = "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "spir-unknown-unknown"
+
+%struct.Example = type { }
+
+define spir_func i32 @foo() {
+  %1 = alloca %struct.Example, align 8
+  call void @_Z3booi(ptr sret(%struct.Example) align 8 %1, i32 noundef 42)
+  ret i32 0
+}
+
+declare void @_Z3booi(ptr sret(%struct.Example) align 8, i32 noundef)