[llvm] [ExtendLifetimes] Implement llvm.fake.use to extend variable lifetimes (PR #86149)

[Matt Arsenault via llvm-commits]

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@@ -0,0 +1,53 @@
+; RUN: opt -mtriple=x86_64-unknown-unknown -S -codegenprepare <%s -o - | FileCheck %s
+;
+; Ensure return instruction splitting ignores fake uses.
+;
+; IR Generated with clang -O2 -S -emit-llvm -fextend-lifetimes test.cpp
+;
+;// test.cpp
+;extern int bar(int);
+;
+;int foo2(int i)
+;{
+;  --i;
+;  if (i <= 0)
+;    return -1;
+;  return bar(i);
+;}
+
+; ModuleID = 'test.cpp'
+source_filename = "test.cpp"
+target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-unknown-unknown"
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arsenm wrote:

Don't need this 

https://github.com/llvm/llvm-project/pull/86149