Use IRParser instead of BitcodeReader (#3399)

The IRParser offers a higher level API, that allows us to also read
bitcode assembly, and not only compiled bitcode.

This allows us to skip the `llvm-as %s -o %t.bc` step in several tests.
I've only updated 3 tests to show the difference; but we have more than
500 occurrences of `llvm-as %s -o` in the tests:

> $ grep -r "llvm-as %s -o" | cut -d':' -f1 | sort -u | wc -l
> 506

As a bonus, the function `llvm::getLazyIRFileModule`
(https://llvm.org/doxygen/namespacellvm.html#aac226baa3ffd0f255a8d2b6d978b81b2)
also calls `MemoryBuffer::getFileOrSTDIN`.

Original commit:
KhronosGroup/SPIRV-LLVM-Translator@400be5144443c6f

Author: jmmartinez

llvm-spirv/test/addrspacecast_null.ll

@@ -1,6 +1,5 @@
 ; REQUIRES: spirv-dis
-; RUN: llvm-as %s -o %t.bc
-; RUN: llvm-spirv %t.bc -o %t.spv
+; RUN: llvm-spirv %s -o %t.spv
 ; RUN: spirv-dis %t.spv | FileCheck %s
 
 ; Test that addrspacecast of null pointer generates appropriate OpConstantNull

llvm-spirv/test/align-duplicate.ll

@@ -1,5 +1,4 @@
-; RUN: llvm-as %s -o %t.bc
-; RUN: llvm-spirv %t.bc -o %t.spv
+; RUN: llvm-spirv %s -o %t.spv
 ; RUN: spirv-val %t.spv
 
 ; Test that duplicate align information does not result in SPIR-V validation

llvm-spirv/test/array-alloca.ll

@@ -1,18 +1,17 @@
-; RUN: llvm-as %s -o %t.bc
-; RUN: llvm-spirv %t.bc -o %t.spv
+; RUN: llvm-spirv %s -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
+; RUN: llvm-spirv %s -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
 
-; RUN: llvm-spirv %t.bc -o %t.spv --spirv-ext=+SPV_KHR_untyped_pointers
+; RUN: llvm-spirv %s -o %t.spv --spirv-ext=+SPV_KHR_untyped_pointers
 ; RUN: spirv-val %t.spv
-; RUN: llvm-spirv %t.bc -spirv-text --spirv-ext=+SPV_KHR_untyped_pointers -o - | FileCheck %s --check-prefix=CHECK-SPIRV
+; RUN: llvm-spirv %s -spirv-text --spirv-ext=+SPV_KHR_untyped_pointers -o - | FileCheck %s --check-prefix=CHECK-SPIRV
 ; 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"

llvm-spirv/tools/llvm-spirv/CMakeLists.txt

@@ -4,6 +4,7 @@ set(LLVM_LINK_COMPONENTS
   BitReader
   BitWriter
   Core
+  IRReader
   Passes
   Support
   TargetParser

llvm-spirv/tools/llvm-spirv/llvm-spirv.cpp

@@ -49,11 +49,11 @@
 #include "llvm/ADT/APInt.h"
 #include "llvm/ADT/SmallVector.h"
 #include "llvm/ADT/StringRef.h"
-#include "llvm/Bitcode/BitcodeReader.h"
 #include "llvm/Bitcode/BitcodeWriter.h"
 #include "llvm/IR/LLVMContext.h"
 #include "llvm/IR/Module.h"
 #include "llvm/IR/Verifier.h"
+#include "llvm/IRReader/IRReader.h"
 #include "llvm/Support/CommandLine.h"
 #include "llvm/Support/Debug.h"
 #include "llvm/Support/Error.h"
@@ -62,6 +62,7 @@
 #include "llvm/Support/MemoryBuffer.h"
 #include "llvm/Support/PrettyStackTrace.h"
 #include "llvm/Support/Signals.h"
+#include "llvm/Support/SourceMgr.h"
 #include "llvm/Support/ToolOutputFile.h"
 #include "llvm/Support/raw_ostream.h"
 
@@ -375,11 +376,14 @@ class StreambufToArray : public std::streambuf {
 static int convertLLVMToSPIRV(const SPIRV::TranslatorOpts &Opts) {
   LLVMContext Context;
 
-  std::unique_ptr<MemoryBuffer> MB =
-      ExitOnErr(errorOrToExpected(MemoryBuffer::getFileOrSTDIN(InputFile)));
-  std::unique_ptr<Module> M =
-      ExitOnErr(getOwningLazyBitcodeModule(std::move(MB), Context,
-                                           /*ShouldLazyLoadMetadata=*/true));
+  SMDiagnostic GetIRErr;
+  std::unique_ptr<Module> M = getLazyIRFileModule(
+      InputFile, GetIRErr, Context, /*ShouldLazyLoadMetadata=*/true);
+  if (!M) {
+    ExitOnErr(
+        createStringError(inconvertibleErrorCode(), GetIRErr.getMessage()));
+  }
+
   ExitOnErr(M->materializeAll());
 
   if (OutputFile.empty()) {