[llvm] [RFC][InstCombine] Combine fence with target specific sync scope (PR #93939)

[Sameer Sahasrabuddhe via llvm-commits]

================
@@ -30,6 +30,15 @@ define void @test_target_dependent_scope() {
   ret void
 }
 
+; CHECK-LABEL: combine_target_dependent_scope
+; CHECK-NEXT: fence syncscope("agent") seq_cst
+; CHECK-NEXT: ret void
+define void @combine_target_dependent_scope() {
+  fence syncscope("agent") acq_rel
+  fence syncscope("agent") seq_cst
+  ret void
+}
+
----------------
ssahasra wrote:

While it's safe to ignore and drop all MMRA, the ideal thing to do is compute the correct MMRA for the final fence. I don't know that is already happening in this path of InstCombine.

@Pierre-vh 

https://github.com/llvm/llvm-project/pull/93939