[llvm] c50415b - [AArch64] Do not promote scalable constants to global variables (#146926)

[via llvm-commits]

Author: Momchil Velikov
Date: 2025-07-07T09:17:31+01:00
New Revision: c50415bb82a740426a5559ff7f1e350f394e9fcf

URL: https://github.com/llvm/llvm-project/commit/c50415bb82a740426a5559ff7f1e350f394e9fcf
DIFF: https://github.com/llvm/llvm-project/commit/c50415bb82a740426a5559ff7f1e350f394e9fcf.diff

LOG: [AArch64] Do not promote scalable constants to global variables (#146926)

Following
https://github.com/llvm/llvm-project/commit/878d3594ed74cd1153bc5cba2cb7a449702cdf34
IREE/MLIR started generating values like

    [<vscale x 4 x float> zeroinitializer, <vscale x 4 x float> poison]

which then LLVM promoted to global variables in `AArch64PromoteConstant` pass.
This patch prevents it by explicitly checking the type of the promotion candidate.

Added: 
    llvm/test/CodeGen/AArch64/no-promote-scalabale-const-to-global.ll

Modified: 
    llvm/lib/Target/AArch64/AArch64PromoteConstant.cpp

Removed: 
    


################################################################################
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
+}