[clang] [flang] [llvm] add -floop-fuse to clang and flang (PR #142686)

[Madhur Amilkanthwar via llvm-commits]

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@@ -204,6 +205,10 @@ static cl::opt<bool>
     EnableLoopInterchange("enable-loopinterchange", cl::init(false), cl::Hidden,
                           cl::desc("Enable the LoopInterchange Pass"));
 
+static cl::opt<bool> EnableLoopFusion("enable-loopfusion", cl::init(false),
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madhur13490 wrote:

As I said, I am taking over this patch from Sebastian. Your comment makes me think.

The primary purpose of this patch is to user-facing option to allow turning fusion on or off. Not everyone is aware of the options provided by developer tools like opt. 

I see the precedence in the code. In `flang/include/flang/Frontend/CodegenOptions.def` I see options for loop-versioning, unrolling etc. 
I see clang and flang differ here. clang doesn't seem to have such options except for `floop-interchange`.  

`floop-interchange` was introduced in https://github.com/llvm/llvm-project/pull/125830 

Having `fexperimental-loop-fusion` is more of syntactic sugar and convenience is based on the same principles of https://github.com/llvm/llvm-project/pull/125830.

I can remove the change from `PassBuilderPipelines.cpp` i.e. EnableFusion, as it can be redundant.



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