[PATCH] D63174: [clang][NewPM] Add RUNS for tests that produce slightly different IR under new PM

[Chandler Carruth via Phabricator via cfe-commits]

chandlerc added a comment.

This really confused me. We shouldn't be seeing this kind of difference in the new PM.

But I think I figured it out.

Both PMs have to run *some* inliner at -O0. This is because we need to inline `always_inline` functions. The new PM has a *super* simple (and fast compile-time wise) inliner designed for this. It's really good at its job. The old PM runs the normal inliner. This thing isn't simple at all. It does complex stuff to incrementally simplify code while inlining because that can have a huge effect on the overall efficiency of the compiler *when doing full optimization passes*. But we're not doing that.

The result is that because all of these tests check code that is emitted by `always_inline` functions in our builtin headers, and then *inlined* into the test functions, the inliner in the old pass manager did a bunch of "cleanup" of the code that the new PM doesn't do.

Honestly, I think the new PM's behavior is correct for -O0, but I think it makes these tests less easy to understand. I think we should instead change the command running here, and when we do I think we will find a set of checks that work for both PMs.

When we are willing to do something like run `opt` in addition to clang (the `convergent.cl` case), instead of just doing `-instnamer` we should also do `-instcombine`. I suspect this will remove the differences.

When we're just directly using `%clang_cc1` I suspect that rather than checking the completely unoptimized code we should check with `-O1` to make the IR much more stable and easy to inspect. It should also result in identical results from the two PMs.



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Comment at: clang/test/CodeGenOpenCL/convergent.cl:2
+// RUN: %clang_cc1 -triple spir-unknown-unknown -emit-llvm %s -o - -fno-experimental-new-pass-manager | opt -instnamer -S | FileCheck -enable-var-scope %s --check-prefixes=CHECK,CHECK-LEGACY
+// RUN: %clang_cc1 -triple spir-unknown-unknown -emit-llvm %s -o - -fexperimental-new-pass-manager | opt -instnamer -S | FileCheck -enable-var-scope %s --check-prefixes=CHECK,CHECK-NEWPM
 
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Probably want to use `opt -passes=instnamer` or some such to use the new PM in the `opt` invocation as well...


Repository:
  rG LLVM Github Monorepo

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  https://reviews.llvm.org/D63174/new/

https://reviews.llvm.org/D63174