[llvm] [MachinePipeliner] Improve loop carried dependence analysis (PR #94185)

[via llvm-commits]

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@@ -1,14 +1,15 @@
 # RUN: llc -mtriple=hexagon -run-pass pipeliner -debug-only=pipeliner %s -o /dev/null 2>&1 -pipeliner-experimental-cg=true | FileCheck %s
 # REQUIRES: asserts
 
-# Test that the loop carried dependence check correctly identifies a recurrence
+# Test that it correctly recognizes that there is no loop carried dependence
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bcahoon wrote:

There is a loop carried dependence here. The dependence is two iterations later. The pipeliner doesn't currently model the dependence distance, so it needs to be conservative.
 
 iteration 0 :  load from X
                     store to X-8
 iteration 1 : load from X-4
                     store to X-12
 iteration 2 : load from X-8 <= there is a dependence to the store in iteration 0
                    store to X-16

https://github.com/llvm/llvm-project/pull/94185