[llvm] remove references to hard-coded gc strategies (PR #94401)

[Dwight Guth via llvm-commits]

https://github.com/dwightguth created https://github.com/llvm/llvm-project/pull/94401

There remains a few places in the LLVM codebase where, instead of using the GC strategy object to decide whether or not to make use of a particular piece of statepoint-related logic, we are still checking the gc strategy name against a hard-coded string. This is obviously undesirable because it means that plugins cannot easily make use of this functionality to create their own GC strategies without sacrificing some of the logic that is supposedly available to them.

This PR quite simply replaces these call sites with calls to `getGCStrategy`, which returns a GCStrategy object for a particular named strategy, and then calls the relevant getter methods on the resulting GCStrategy pointer.

>From 7d6930cb2d3a0b4f705cee709016984e471f2276 Mon Sep 17 00:00:00 2001
From: Dwight Guth <dwight.guth at runtimeverification.com>
Date: Tue, 4 Jun 2024 14:57:51 -0500
Subject: [PATCH] remove references to hard-coded gc strategies

There remains a few places in the LLVM codebase where, instead of
using the GC strategy object to decide whether or not to make use
of a particular piece of statepoint-related logic, we are still
checking the gc strategy name against a hard-coded string. This
is obviously undesirable because it means that plugins cannot
easily make use of this functionality to create their own GC
strategies without sacrificing some of the logic that is supposedly
available to them.

This PR quite simply replaces these call sites with calls to
`getGCStrategy`, which returns a GCStrategy object for a particular
named strategy, and then calls the relevant getter methods on the
resulting GCStrategy pointer.
---
 llvm/lib/IR/Value.cpp                          | 12 +++++-------
 llvm/lib/Transforms/Scalar/PlaceSafepoints.cpp |  9 +++------
 2 files changed, 8 insertions(+), 13 deletions(-)

diff --git a/llvm/lib/IR/Value.cpp b/llvm/lib/IR/Value.cpp
index 8522747ccf128..042e442b31efb 100644
--- a/llvm/lib/IR/Value.cpp
+++ b/llvm/lib/IR/Value.cpp
@@ -20,6 +20,7 @@
 #include "llvm/IR/DebugInfo.h"
 #include "llvm/IR/DerivedTypes.h"
 #include "llvm/IR/DerivedUser.h"
+#include "llvm/IR/GCStrategy.h"
 #include "llvm/IR/GetElementPtrTypeIterator.h"
 #include "llvm/IR/InstrTypes.h"
 #include "llvm/IR/Instructions.h"
@@ -826,14 +827,11 @@ bool Value::canBeFreed() const {
   // which is why we need the explicit opt in on a per collector basis.
   if (!F->hasGC())
     return true;
-  
-  const auto &GCName = F->getGC();
-  if (GCName == "statepoint-example") {
+
+  const auto &GCStrategy = getGCStrategy(F->getGC());
+  if (GCStrategy->useStatepoints()) {
     auto *PT = cast<PointerType>(this->getType());
-    if (PT->getAddressSpace() != 1)
-      // For the sake of this example GC, we arbitrarily pick addrspace(1) as
-      // our GC managed heap.  This must match the same check in
-      // RewriteStatepointsForGC (and probably needs better factored.)
+    if (GCStrategy->isGCManagedPointer(PT) == false)
       return true;
 
     // It is cheaper to scan for a declaration than to scan for a use in this
diff --git a/llvm/lib/Transforms/Scalar/PlaceSafepoints.cpp b/llvm/lib/Transforms/Scalar/PlaceSafepoints.cpp
index dcdea6e7b62ae..2775dbd149f54 100644
--- a/llvm/lib/Transforms/Scalar/PlaceSafepoints.cpp
+++ b/llvm/lib/Transforms/Scalar/PlaceSafepoints.cpp
@@ -58,6 +58,7 @@
 #include "llvm/Analysis/ScalarEvolution.h"
 #include "llvm/Analysis/TargetLibraryInfo.h"
 #include "llvm/IR/Dominators.h"
+#include "llvm/IR/GCStrategy.h"
 #include "llvm/IR/IntrinsicInst.h"
 #include "llvm/IR/LegacyPassManager.h"
 #include "llvm/IR/Statepoint.h"
@@ -600,13 +601,9 @@ static bool isGCSafepointPoll(Function &F) {
 /// polls and parseable call sites.  The main point of this function is to be
 /// an extension point for custom logic.
 static bool shouldRewriteFunction(Function &F) {
-  // TODO: This should check the GCStrategy
   if (F.hasGC()) {
-    const auto &FunctionGCName = F.getGC();
-    const StringRef StatepointExampleName("statepoint-example");
-    const StringRef CoreCLRName("coreclr");
-    return (StatepointExampleName == FunctionGCName) ||
-           (CoreCLRName == FunctionGCName);
+    const auto &GCStrategy = getGCStrategy(F.getGC());
+    return GCStrategy->useStatepoints();
   } else
     return false;
 }