Fix #8455 (in combination with #8457) (#8456)

* Partial fix for #8455

In slice_vector(), only check for type equality after vectors have been normalized to fixed (i.e., it's ok for some original input to be vscale)

* Update CodeGen_LLVM.h

src/CodeGen_LLVM.cpp

@@ -4947,11 +4947,18 @@ Value *CodeGen_LLVM::concat_vectors(const vector<Value *> &v) {
 
 Value *CodeGen_LLVM::shuffle_vectors(Value *a, Value *b,
                                      const std::vector<int> &indices) {
-    internal_assert(a->getType() == b->getType());
+    if (isa<llvm::ScalableVectorType>(a->getType())) {
+        a = scalable_to_fixed_vector_type(a);
+    }
+    if (isa<llvm::ScalableVectorType>(b->getType())) {
+        b = scalable_to_fixed_vector_type(b);
+    }
     if (!a->getType()->isVectorTy()) {
         a = create_broadcast(a, 1);
         b = create_broadcast(b, 1);
     }
+    // Check for type identity *after* normalizing to fixed vectors
+    internal_assert(a->getType() == b->getType());
     vector<Constant *> llvm_indices(indices.size());
     for (size_t i = 0; i < llvm_indices.size(); i++) {
         if (indices[i] >= 0) {
@@ -4963,12 +4970,6 @@ Value *CodeGen_LLVM::shuffle_vectors(Value *a, Value *b,
             llvm_indices[i] = PoisonValue::get(i32_t);
         }
     }
-    if (isa<llvm::ScalableVectorType>(a->getType())) {
-        a = scalable_to_fixed_vector_type(a);
-    }
-    if (isa<llvm::ScalableVectorType>(b->getType())) {
-        b = scalable_to_fixed_vector_type(b);
-    }
     return builder->CreateShuffleVector(a, b, ConstantVector::get(llvm_indices));
 }
 

src/CodeGen_LLVM.h

@@ -489,7 +489,9 @@ class CodeGen_LLVM : public IRVisitor {
     /** Concatenate a bunch of llvm vectors. Must be of the same type. */
     virtual llvm::Value *concat_vectors(const std::vector<llvm::Value *> &);
 
-    /** Create an LLVM shuffle vectors instruction. */
+    /** Create an LLVM shuffle vectors instruction. Takes a combination of
+     * fixed or scalable vectors as input, so long as the effective lengths match,
+     * but always returns a fixed vector. */
     virtual llvm::Value *shuffle_vectors(llvm::Value *a, llvm::Value *b,
                                          const std::vector<int> &indices);
     /** Shorthand for shuffling a single vector. */