[llvm] [TableGen] Ignore inaccessible memory when checking pattern flags (PR #90061)

[Jay Foad via llvm-commits]

https://github.com/jayfoad created https://github.com/llvm/llvm-project/pull/90061

In the AMDGPU backend we have some cases where we'd like to mark an
intrinsic as IntrInaccessibleMemOnly to model dependencies, but the
corresponding MachineInstrs use uses/defs of a special physical register
to express the same thing. In this case TableGen would complain:

  Pattern doesn't match mayLoad/mayStore = 0

but the error is not useful.


>From 7b4f315029445fd97c17df0bc925fab1e61a2aac Mon Sep 17 00:00:00 2001
From: Jay Foad <jay.foad at amd.com>
Date: Thu, 25 Apr 2024 15:13:55 +0100
Subject: [PATCH] [TableGen] Ignore inaccessible memory when checking pattern
 flags

In the AMDGPU backend we have some cases where we'd like to mark an
intrinsic as IntrInaccessibleMemOnly to model dependencies, but the
corresponding MachineInstrs use uses/defs of a special physical register
to express the same thing. In this case TableGen would complain:

  Pattern doesn't match mayLoad/mayStore = 0

but the error is not useful.
---
 llvm/utils/TableGen/Common/CodeGenDAGPatterns.cpp | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/llvm/utils/TableGen/Common/CodeGenDAGPatterns.cpp b/llvm/utils/TableGen/Common/CodeGenDAGPatterns.cpp
index 7a5d2be3ae95b2..e0144a9d8ed2a7 100644
--- a/llvm/utils/TableGen/Common/CodeGenDAGPatterns.cpp
+++ b/llvm/utils/TableGen/Common/CodeGenDAGPatterns.cpp
@@ -3616,7 +3616,15 @@ class InstAnalyzer {
       hasChain = true;
 
     if (const CodeGenIntrinsic *IntInfo = N.getIntrinsicInfo(CDP)) {
-      ModRefInfo MR = IntInfo->ME.getModRef();
+      // Ignore reads/writes to inaccessible memory. These should not imply
+      // mayLoad/mayStore on the instruction because they are often used to
+      // model dependencies that Machine IR expresses as uses/defs of a
+      // special physical register.
+      ModRefInfo MR = ModRefInfo::NoModRef;
+      for (MemoryEffects::Location Loc : MemoryEffects::locations()) {
+        if (Loc != MemoryEffects::Location::InaccessibleMem)
+          MR |= IntInfo->ME.getModRef();
+      }
       // If this is an intrinsic, analyze it.
       if (isRefSet(MR))
         mayLoad = true; // These may load memory.