From ddeab9879e434589588f9d12291a4d79d0ee0349 Mon Sep 17 00:00:00 2001
From: Massimiliano Culpo <massimiliano.culpo@gmail.com>
Date: Fri, 7 Feb 2025 19:40:07 +0100
Subject: [PATCH] Improve stability of DAG when using multiple compilers for
 the same language

---
 lib/spack/spack/solver/concretize.lp            | 17 ++++++++++++++++-
 .../packages/intel-oneapi-compilers/package.py  |  3 +--
 2 files changed, 17 insertions(+), 3 deletions(-)

diff --git a/lib/spack/spack/solver/concretize.lp b/lib/spack/spack/solver/concretize.lp
index 7e9052af779..3ee427c35c7 100644
--- a/lib/spack/spack/solver/concretize.lp
+++ b/lib/spack/spack/solver/concretize.lp
@@ -1246,6 +1246,10 @@ error(100, "Cannot propagate the variant '{0}' from the package: {1} because pac
 % 1. The same flag type is not set on this node
 % 2. This node has the same compilers as the propagation source
 
+compiler_penalty(PackageNode, C-1) :-
+   C = #count { CompilerNode : node_compiler(PackageNode, CompilerNode) },
+   node_compiler(PackageNode, _).
+
 node_compiler(node(X, Package), node(Y, Compiler)) :-
      attr("virtual_on_edge", node(X, Package), node(Y, Compiler), Language),
      attr("version", node(Y, Compiler), Version),
@@ -1683,7 +1687,7 @@ opt_criterion(50, "number of non-default variants (non-roots)").
       build_priority(PackageNode, Priority)
 }.
 
-% Minimize the weights of the providers, i.e. use as much as
+% Minimize the ids of the providers, i.e. use as much as
 % possible the first providers
 opt_criterion(48, "number of duplicate virtuals needed").
 #minimize{ 0@248: #true }.
@@ -1694,6 +1698,16 @@ opt_criterion(48, "number of duplicate virtuals needed").
       build_priority(ProviderNode, Priority)
 }.
 
+% Minimize the number of compilers used on nodes
+opt_criterion(49, "minimize the number of compilers used on the same node").
+#minimize{ 0@249: #true }.
+#minimize{ 0@49: #true }.
+#minimize{
+    Penalty@49+Priority,PackageNode
+    : compiler_penalty(PackageNode, Penalty),
+    build_priority(PackageNode, Priority)
+}.
+
 % Minimize the weights of the providers, i.e. use as much as
 % possible the most preferred providers
 opt_criterion(45, "preferred providers (non-roots)").
@@ -1792,6 +1806,7 @@ opt_criterion(1, "edge wiring").
       depends_on(ParentNode, PackageNode)
 }.
 
+
 #minimize{ 0@201: #true }.
 #minimize{ 0@1: #true }.
 #minimize{
diff --git a/var/spack/repos/builtin/packages/intel-oneapi-compilers/package.py b/var/spack/repos/builtin/packages/intel-oneapi-compilers/package.py
index 5fb644e5c8b..7b0cf15214d 100644
--- a/var/spack/repos/builtin/packages/intel-oneapi-compilers/package.py
+++ b/var/spack/repos/builtin/packages/intel-oneapi-compilers/package.py
@@ -356,8 +356,7 @@ class IntelOneapiCompilers(IntelOneApiPackage, CompilerPackage):
 
     stdcxx_libs = ("-cxxlib",)
 
-    provides("c")
-    provides("cxx")
+    provides("c", "cxx")
     provides("fortran")
 
     def _standard_flag(self, *, language, standard):