[llvm] [SPIR-V][Codegen] Represent the property of the target to declare and use typed pointers and update MachineVerifier to use it (PR #110270)

[Vyacheslav Levytskyy via llvm-commits]

https://github.com/VyacheslavLevytskyy created https://github.com/llvm/llvm-project/pull/110270

When MachineVerifier validates G_BITCAST we see a check of a kind: `if Source Type is equal to Destination Type then report error "bitcast must change the type"`. This doesn't take into account the notion of a typed pointer that is important for SPIR-V where a user may and should use bitcast between pointers with different pointee types (see, https://registry.khronos.org/SPIR-V/specs/unified1/SPIRV.html#OpBitcast). It's important for correct lowering in SPIR-V, because interpretation of the data type is not left to instructions that utilize the pointer, but encoded by the pointer declaration, and if the SPIRV target can and must handle the declaration and use of pointers that specify the type of data they point to.

It's not feasible to improve validation of G_BITCAST using just information provided by low level types of source and destination. This PR proposes a solution by introducing a new class member `hasTypedPointer()` to represent the required target lowering property. This function is used then by MachineVerifier to allow for pointer type source and destination operands, and is overridden by SPIRV implementation of target lowering rules.

 where SrcTy and DstTy both being LLT pointers just have no means to express the notion of pointer type that is important for SPIR-V where a user may and should use bitcast between pointers with different pointee types (see, https://registry.khronos.org/SPIR-V/specs/unified1/SPIRV.html#OpBitcast).

This PR helps to MachineVerifier to take into account the notion of typed pointers when checking G_BITCAST validity.

>From 70501ec2cc3167ed9f68061f5906bfaddc9c6993 Mon Sep 17 00:00:00 2001
From: "Levytskyy, Vyacheslav" <vyacheslav.levytskyy at intel.com>
Date: Fri, 27 Sep 2024 06:31:16 -0700
Subject: [PATCH] MachineVerifier takes into account the notion of typed
 pointers when checking G_BITCAST validity

---
 llvm/include/llvm/CodeGen/TargetLowering.h        |  6 ++++++
 llvm/lib/CodeGen/MachineVerifier.cpp              |  4 +++-
 llvm/lib/Target/SPIRV/SPIRVISelLowering.h         |  3 +++
 .../SPIRV/test_typedptr_bitcast.mir               | 15 +++++++++++++++
 4 files changed, 27 insertions(+), 1 deletion(-)
 create mode 100644 llvm/test/MachineVerifier/SPIRV/test_typedptr_bitcast.mir

diff --git a/llvm/include/llvm/CodeGen/TargetLowering.h b/llvm/include/llvm/CodeGen/TargetLowering.h
index 3842af56e6b3d7..19113de188d43d 100644
--- a/llvm/include/llvm/CodeGen/TargetLowering.h
+++ b/llvm/include/llvm/CodeGen/TargetLowering.h
@@ -455,6 +455,12 @@ class TargetLoweringBase {
     return true;
   }
 
+  /// Return true if the target can handle the declaration and use of pointers
+  /// that specify the type of data they point to, meaning that interpretation
+  /// of the data type is not left to instructions that utilize the pointer, but
+  /// encoded by the pointer declaration.
+  virtual bool hasTypedPointer() const { return false; }
+
   /// Return true if the @llvm.experimental.vector.partial.reduce.* intrinsic
   /// should be expanded using generic code in SelectionDAGBuilder.
   virtual bool
diff --git a/llvm/lib/CodeGen/MachineVerifier.cpp b/llvm/lib/CodeGen/MachineVerifier.cpp
index 24a0f41775cc1d..1131ab053814a7 100644
--- a/llvm/lib/CodeGen/MachineVerifier.cpp
+++ b/llvm/lib/CodeGen/MachineVerifier.cpp
@@ -1294,7 +1294,9 @@ void MachineVerifier::verifyPreISelGenericInstruction(const MachineInstr *MI) {
       report("bitcast sizes must match", MI);
 
     if (SrcTy == DstTy)
-      report("bitcast must change the type", MI);
+      if (!SrcTy.isPointer() ||
+          !MF->getSubtarget().getTargetLowering()->hasTypedPointer())
+        report("bitcast must change the type", MI);
 
     break;
   }
diff --git a/llvm/lib/Target/SPIRV/SPIRVISelLowering.h b/llvm/lib/Target/SPIRV/SPIRVISelLowering.h
index 77356b7512a739..18d463d78a7f65 100644
--- a/llvm/lib/Target/SPIRV/SPIRVISelLowering.h
+++ b/llvm/lib/Target/SPIRV/SPIRVISelLowering.h
@@ -41,6 +41,9 @@ class SPIRVTargetLowering : public TargetLowering {
   // prevent creation of jump tables
   bool areJTsAllowed(const Function *) const override { return false; }
 
+  // allow for typed pointers
+  bool hasTypedPointer() const override { return true; }
+
   // This is to prevent sexts of non-i64 vector indices which are generated
   // within general IRTranslator hence type generation for it is omitted.
   MVT getVectorIdxTy(const DataLayout &DL) const override {
diff --git a/llvm/test/MachineVerifier/SPIRV/test_typedptr_bitcast.mir b/llvm/test/MachineVerifier/SPIRV/test_typedptr_bitcast.mir
new file mode 100644
index 00000000000000..cb0ff5863f6215
--- /dev/null
+++ b/llvm/test/MachineVerifier/SPIRV/test_typedptr_bitcast.mir
@@ -0,0 +1,15 @@
+#RUN: llc -mtriple=spirv64-unknown-unknown -o - -global-isel -run-pass=none -verify-machineinstrs %s 2>&1 | FileCheck %s
+
+---
+name:            test_typedptr_bitcast
+legalized:       true
+regBankSelected: false
+selected:        false
+tracksRegLiveness: true
+liveins:
+body:             |
+  bb.0:
+    ; CHECK-NOT: Bad machine code: bitcast must change the type
+    %0:_(p0) = G_IMPLICIT_DEF
+    %1:_(p0) = G_BITCAST %0
+...