nir: add nir_instr_can_speculate helper (for LICM)

Acked-by: Job Noorman <job@noorman.info>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/36099>

src/compiler/nir/nir.c

@@ -2728,6 +2728,47 @@ nir_intrinsic_can_reorder(nir_intrinsic_instr *instr)
           (info->flags & NIR_INTRINSIC_CAN_REORDER);
 }
 
+/* Return whether an instruction returns the same result regardless of where
+ * it's executed in the shader and regardless of whether it's executed multiple
+ * times.
+ */
+bool
+nir_instr_can_speculate(nir_instr *instr)
+{
+   nir_intrinsic_instr *intr;
+
+   switch (instr->type) {
+   case nir_instr_type_undef:
+   case nir_instr_type_load_const:
+   case nir_instr_type_alu:
+   case nir_instr_type_deref:
+      return true;
+
+   case nir_instr_type_tex:
+      return false;
+
+   case nir_instr_type_intrinsic:
+      intr = nir_instr_as_intrinsic(instr);
+
+      if (!nir_intrinsic_can_reorder(intr))
+         return false;
+
+      if (nir_intrinsic_has_access(intr))
+         return nir_intrinsic_access(intr) & ACCESS_CAN_SPECULATE;
+
+      /* Intrinsics without ACCESS are speculatable if they can be reordered. */
+      return true;
+
+   case nir_instr_type_call:
+   case nir_instr_type_jump:
+   case nir_instr_type_phi:
+   case nir_instr_type_parallel_copy:
+      return false;
+   }
+
+   return false;
+}
+
 nir_src *
 nir_get_shader_call_payload_src(nir_intrinsic_instr *call)
 {

src/compiler/nir/nir.h

@@ -2121,7 +2121,7 @@ void nir_rewrite_image_intrinsic(nir_intrinsic_instr *instr,
 
 /* Determine if an intrinsic can be arbitrarily reordered and eliminated. */
 bool nir_intrinsic_can_reorder(nir_intrinsic_instr *instr);
-
+bool nir_instr_can_speculate(nir_instr *instr);
 bool nir_intrinsic_writes_external_memory(const nir_intrinsic_instr *instr);
 
 static inline bool

src/compiler/nir/nir_opt_preamble.c

@@ -102,18 +102,10 @@ typedef struct {
 static bool
 instr_can_speculate(nir_instr *instr)
 {
-   /* Intrinsics with an ACCESS index can only be speculated if they are
-    * explicitly CAN_SPECULATE.
-    */
-   if (instr->type == nir_instr_type_intrinsic) {
-      nir_intrinsic_instr *intr = nir_instr_as_intrinsic(instr);
+   if (instr->type == nir_instr_type_phi)
+      return true;
 
-      if (nir_intrinsic_has_access(intr))
-         return nir_intrinsic_access(intr) & ACCESS_CAN_SPECULATE;
-   }
-
-   /* For now, everything else can be speculated. TODO: Bindless textures. */
-   return true;
+   return nir_instr_can_speculate(instr);
 }
 
 static float