fir crashing with scalable TypeSizes

From 537f3d3a7588d226b86590f97c4401107585e1ce Mon Sep 17 00:00:00 2001
From: Jakob Koschel <jakobkoschel@google.com>
Date: Thu, 5 Mar 2026 01:11:44 +0100
Subject: [PATCH] [SafeStack] Fix crashing with scalable TypeSizes (#180547)

On e.g. aarch64 the TypeSize of scalar types can have a size that is not
known at compile time.
Currently when safestack occurs those it simply crashes as described in
https://github.com/llvm/llvm-project/issues/175868.

gnu/llvm/llvm/lib/CodeGen/SafeStack.cpp

@@ -176,6 +176,8 @@ class SafeStack {
 
   bool IsMemIntrinsicSafe(const MemIntrinsic *MI, const Use &U,
                           const Value *AllocaPtr, uint64_t AllocaSize);
+  bool IsAccessSafe(Value *Addr, TypeSize Size, const Value *AllocaPtr,
+                    uint64_t AllocaSize);
   bool IsAccessSafe(Value *Addr, uint64_t Size, const Value *AllocaPtr,
                     uint64_t AllocaSize);
 
@@ -206,6 +208,16 @@ uint64_t SafeStack::getStaticAllocaAllocationSize(const AllocaInst* AI) {
   return Size;
 }
 
+bool SafeStack::IsAccessSafe(Value *Addr, TypeSize AccessSize,
+                             const Value *AllocaPtr, uint64_t AllocaSize) {
+  if (AccessSize.isScalable()) {
+    // In case we don't know the size at compile time we cannot verify if the
+    // access is safe.
+    return false;
+  }
+  return IsAccessSafe(Addr, AccessSize.getFixedValue(), AllocaPtr, AllocaSize);
+}
+
 bool SafeStack::IsAccessSafe(Value *Addr, uint64_t AccessSize,
                              const Value *AllocaPtr, uint64_t AllocaSize) {
   const SCEV *AddrExpr = SE.getSCEV(Addr);