[llvm] [AArch64] Do not promote scalable constants to global variables (PR #146926)

[Momchil Velikov via llvm-commits]

https://github.com/momchil-velikov updated https://github.com/llvm/llvm-project/pull/146926

>From 88bd451a14e64ba12de16d2ceaa9bd8926d3e341 Mon Sep 17 00:00:00 2001
From: Momchil Velikov <momchil.velikov at arm.com>
Date: Thu, 3 Jul 2025 17:02:36 +0000
Subject: [PATCH] [AArch64] Do not promote scalable constants to global
 variables

---
 .../Target/AArch64/AArch64PromoteConstant.cpp |  4 ++++
 .../no-promote-scalabale-const-to-global.ll   | 20 +++++++++++++++++++
 2 files changed, 24 insertions(+)
 create mode 100644 llvm/test/CodeGen/AArch64/no-promote-scalabale-const-to-global.ll

diff --git a/llvm/lib/Target/AArch64/AArch64PromoteConstant.cpp b/llvm/lib/Target/AArch64/AArch64PromoteConstant.cpp
index 8edf1d0f9296b..3f45d55063b50 100644
--- a/llvm/lib/Target/AArch64/AArch64PromoteConstant.cpp
+++ b/llvm/lib/Target/AArch64/AArch64PromoteConstant.cpp
@@ -345,6 +345,10 @@ static bool shouldConvertImpl(const Constant *Cst) {
   if (Cst->isZeroValue())
     return false;
 
+  // Globals cannot be or contain scalable vectors.
+  if (Cst->getType()->isScalableTy())
+    return false;
+
   if (Stress)
     return true;
 
diff --git a/llvm/test/CodeGen/AArch64/no-promote-scalabale-const-to-global.ll b/llvm/test/CodeGen/AArch64/no-promote-scalabale-const-to-global.ll
new file mode 100644
index 0000000000000..db7d26b6ed139
--- /dev/null
+++ b/llvm/test/CodeGen/AArch64/no-promote-scalabale-const-to-global.ll
@@ -0,0 +1,20 @@
+; RUN: llc -mtriple=aarch64 -mattr=+sve -stop-after=aarch64-promote-const < %s | FileCheck %s
+
+; Test that the constant inside the `phi` is not promoted to a global
+; CHECK-NOT: _PromotedConst
+define void @f(i1 %c, ptr %p, ptr %q) {
+entry:
+  br i1 %c, label %if.then, label %if.else
+
+if.then:
+  %u = load [2 x <vscale x 4 x float> ], ptr %p
+  br label %exit
+
+if.else:
+  br label %exit
+
+exit:
+  %v = phi [2 x <vscale x 4 x float> ]  [ %u, %if.then], [[<vscale x 4 x float> zeroinitializer, <vscale x 4 x float> poison], %if.else]
+  store [2 x <vscale x 4 x float>] %v, ptr %q
+  ret void
+}