[llvm] [NVPTX] Add support for calling aliases (PR #81170)

[Alex MacLean via llvm-commits]

https://github.com/AlexMaclean created https://github.com/llvm/llvm-project/pull/81170

The current implementation of aliases tries to remove all the aliases in the module to prevent the generic version of `AsmPrinter` from emitting them incorrectly. Unfortunately, if the aliases are used this will fail. Instead let's override the function to print aliases directly.

>From d794687f0b3ca06dadc902db3dec4b980d24b1b3 Mon Sep 17 00:00:00 2001
From: Alex MacLean <amaclean at nvidia.com>
Date: Thu, 8 Feb 2024 02:09:09 +0000
Subject: [PATCH] [NVPTX] Add support for calling aliases

---
 llvm/include/llvm/CodeGen/AsmPrinter.h     |  2 +-
 llvm/lib/CodeGen/AsmPrinter/AsmPrinter.cpp |  2 +-
 llvm/lib/Target/NVPTX/NVPTXAsmPrinter.cpp  | 10 ----------
 llvm/lib/Target/NVPTX/NVPTXAsmPrinter.h    |  2 +-
 llvm/test/CodeGen/NVPTX/alias.ll           | 10 ++++++++++
 5 files changed, 13 insertions(+), 13 deletions(-)

diff --git a/llvm/include/llvm/CodeGen/AsmPrinter.h b/llvm/include/llvm/CodeGen/AsmPrinter.h
index fbd198a75a2436..a7fbf4aeb74494 100644
--- a/llvm/include/llvm/CodeGen/AsmPrinter.h
+++ b/llvm/include/llvm/CodeGen/AsmPrinter.h
@@ -897,7 +897,7 @@ class AsmPrinter : public MachineFunctionPass {
   virtual void emitModuleCommandLines(Module &M);
 
   GCMetadataPrinter *getOrCreateGCPrinter(GCStrategy &S);
-  void emitGlobalAlias(Module &M, const GlobalAlias &GA);
+  virtual void emitGlobalAlias(const Module &M, const GlobalAlias &GA);
   void emitGlobalIFunc(Module &M, const GlobalIFunc &GI);
 
 private:
diff --git a/llvm/lib/CodeGen/AsmPrinter/AsmPrinter.cpp b/llvm/lib/CodeGen/AsmPrinter/AsmPrinter.cpp
index b961fc2c338ae7..e89a1c26c23e6b 100644
--- a/llvm/lib/CodeGen/AsmPrinter/AsmPrinter.cpp
+++ b/llvm/lib/CodeGen/AsmPrinter/AsmPrinter.cpp
@@ -2127,7 +2127,7 @@ void AsmPrinter::emitGlobalGOTEquivs() {
     emitGlobalVariable(GV);
 }
 
-void AsmPrinter::emitGlobalAlias(Module &M, const GlobalAlias &GA) {
+void AsmPrinter::emitGlobalAlias(const Module &M, const GlobalAlias &GA) {
   MCSymbol *Name = getSymbol(&GA);
   bool IsFunction = GA.getValueType()->isFunctionTy();
   // Treat bitcasts of functions as functions also. This is important at least
diff --git a/llvm/lib/Target/NVPTX/NVPTXAsmPrinter.cpp b/llvm/lib/Target/NVPTX/NVPTXAsmPrinter.cpp
index 6c4879ba183c0a..3c52751721a3f7 100644
--- a/llvm/lib/Target/NVPTX/NVPTXAsmPrinter.cpp
+++ b/llvm/lib/Target/NVPTX/NVPTXAsmPrinter.cpp
@@ -932,16 +932,6 @@ bool NVPTXAsmPrinter::doFinalization(Module &M) {
     GlobalsEmitted = true;
   }
 
-  // If we have any aliases we emit them at the end.
-  SmallVector<GlobalAlias *> AliasesToRemove;
-  for (GlobalAlias &Alias : M.aliases()) {
-    emitGlobalAlias(M, Alias);
-    AliasesToRemove.push_back(&Alias);
-  }
-
-  for (GlobalAlias *A : AliasesToRemove)
-    A->eraseFromParent();
-
   // call doFinalization
   bool ret = AsmPrinter::doFinalization(M);
 
diff --git a/llvm/lib/Target/NVPTX/NVPTXAsmPrinter.h b/llvm/lib/Target/NVPTX/NVPTXAsmPrinter.h
index 7f0f37e7207d2d..cfd32ba72e5cf0 100644
--- a/llvm/lib/Target/NVPTX/NVPTXAsmPrinter.h
+++ b/llvm/lib/Target/NVPTX/NVPTXAsmPrinter.h
@@ -174,7 +174,7 @@ class LLVM_LIBRARY_VISIBILITY NVPTXAsmPrinter : public AsmPrinter {
   void printModuleLevelGV(const GlobalVariable *GVar, raw_ostream &O,
                           bool processDemoted, const NVPTXSubtarget &STI);
   void emitGlobals(const Module &M);
-  void emitGlobalAlias(const Module &M, const GlobalAlias &GA);
+  void emitGlobalAlias(const Module &M, const GlobalAlias &GA) override;
   void emitHeader(Module &M, raw_ostream &O, const NVPTXSubtarget &STI);
   void emitKernelFunctionDirectives(const Function &F, raw_ostream &O) const;
   void emitVirtualRegister(unsigned int vr, raw_ostream &);
diff --git a/llvm/test/CodeGen/NVPTX/alias.ll b/llvm/test/CodeGen/NVPTX/alias.ll
index d5dc3a12029ae6..df1b7647b49258 100644
--- a/llvm/test/CodeGen/NVPTX/alias.ll
+++ b/llvm/test/CodeGen/NVPTX/alias.ll
@@ -12,6 +12,12 @@ define void @noreturn() #0 {
 }
 @noreturn_alias = alias i32 (), ptr @noreturn
 
+define i32 @z() {
+  %val = call i32 @b()
+  ret i32 %val
+}
+
+
 attributes #0 = { noreturn }
 
 ; CHECK: .visible .func  (.param .b32 func_retval0) a()
@@ -24,6 +30,10 @@ attributes #0 = { noreturn }
 ;      CHECK: .visible .func noreturn()
 ; CHECK-NEXT: .noreturn
 
+;      CHECK: .visible .func  (.param .b32 func_retval0) z()
+;      CHECK:      call.uni (retval0), 
+; CHECK-NEXT:      b,
+
 ;      CHECK: .visible .func  (.param .b32 func_retval0) b();
 ; CHECK-NEXT: .alias b, a;