[llvm] [AMDGPU][MC] Allow UC_VERSION_* constant reuse (PR #96461)

[Carl Ritson via llvm-commits]

https://github.com/perlfu updated https://github.com/llvm/llvm-project/pull/96461

>From 88595f24da33f71db1ea33c08b5e5fdb03a3ab0b Mon Sep 17 00:00:00 2001
From: Carl Ritson <carl.ritson at amd.com>
Date: Mon, 24 Jun 2024 17:32:41 +0900
Subject: [PATCH 1/2] [AMDGPU][MC] Allow UC_VERSION_* constant reuse

If more than one disassembler is created for a context then
allow reuse of existing constants.
Update assertion to validate constant contents.
---
 .../lib/Target/AMDGPU/Disassembler/AMDGPUDisassembler.cpp | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/llvm/lib/Target/AMDGPU/Disassembler/AMDGPUDisassembler.cpp b/llvm/lib/Target/AMDGPU/Disassembler/AMDGPUDisassembler.cpp
index 76a559c9443bd..d61e8ebb866df 100644
--- a/llvm/lib/Target/AMDGPU/Disassembler/AMDGPUDisassembler.cpp
+++ b/llvm/lib/Target/AMDGPU/Disassembler/AMDGPUDisassembler.cpp
@@ -2366,8 +2366,12 @@ const MCExpr *AMDGPUDisassembler::createConstantSymbolExpr(StringRef Id,
                                                            int64_t Val) {
   MCContext &Ctx = getContext();
   MCSymbol *Sym = Ctx.getOrCreateSymbol(Id);
-  assert(!Sym->isVariable());
-  Sym->setVariableValue(MCConstantExpr::create(Val, Ctx));
+  int64_t Res = ~Val;
+  assert(!Sym->isVariable() ||
+         (Sym->getVariableValue()->evaluateAsAbsolute(Res) && Res == Val));
+  (void)Res;
+  if (!Sym->isVariable())
+    Sym->setVariableValue(MCConstantExpr::create(Val, Ctx));
   return MCSymbolRefExpr::create(Sym, Ctx);
 }
 

>From 053a7341bb0beb9f7c21ff29454cf70334068120 Mon Sep 17 00:00:00 2001
From: Carl Ritson <carl.ritson at amd.com>
Date: Tue, 25 Jun 2024 09:39:50 +0900
Subject: [PATCH 2/2] Address reviewer feedback: - Change assertion to comment

---
 llvm/lib/Target/AMDGPU/Disassembler/AMDGPUDisassembler.cpp | 7 +++----
 1 file changed, 3 insertions(+), 4 deletions(-)

diff --git a/llvm/lib/Target/AMDGPU/Disassembler/AMDGPUDisassembler.cpp b/llvm/lib/Target/AMDGPU/Disassembler/AMDGPUDisassembler.cpp
index d61e8ebb866df..875d1a16a1d56 100644
--- a/llvm/lib/Target/AMDGPU/Disassembler/AMDGPUDisassembler.cpp
+++ b/llvm/lib/Target/AMDGPU/Disassembler/AMDGPUDisassembler.cpp
@@ -2366,10 +2366,9 @@ const MCExpr *AMDGPUDisassembler::createConstantSymbolExpr(StringRef Id,
                                                            int64_t Val) {
   MCContext &Ctx = getContext();
   MCSymbol *Sym = Ctx.getOrCreateSymbol(Id);
-  int64_t Res = ~Val;
-  assert(!Sym->isVariable() ||
-         (Sym->getVariableValue()->evaluateAsAbsolute(Res) && Res == Val));
-  (void)Res;
+  // Note: only set value to Val on a new symbol.
+  // Existing symbol may potentially have a different value to the one
+  // requested, which allows for user redefinition of symbols.
   if (!Sym->isVariable())
     Sym->setVariableValue(MCConstantExpr::create(Val, Ctx));
   return MCSymbolRefExpr::create(Sym, Ctx);