[clang] [flang] [llvm] Introduce -fexperimental-loop-fuse to clang and flang (PR #142686)

[Madhur Amilkanthwar via cfe-commits]

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@@ -52,6 +52,15 @@
 // CHECK-INTERCHANGE-LOOPS: "-floop-interchange"
 // CHECK-NO-INTERCHANGE-LOOPS: "-fno-loop-interchange"
 
+// RUN: %clang -### -S -fexperimental-loop-fusion %s 2>&1 | FileCheck -check-prefix=CHECK-FUSE-LOOPS %s
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madhur13490 wrote:

I don't think this is usually done or necessary. I checked other options, which are introduced by `addOptInFlag`, namely `funique_internal_linkage_names`, `fseparate_named_sections`, `fatomic_ignore_denormal_mode`, `fsplit_stack`, and many others, and I don't see any precedence of having a test which checks if the negative options are recognized.

Do we want to make an exception for this?

https://github.com/llvm/llvm-project/pull/142686