[llvm] [CodeGen] Merge lowerConstantIntrinsics into pre-isel lowering (PR #97727)

[Björn Pettersson via llvm-commits]

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@@ -96,8 +96,8 @@ static bool replaceConditionalBranchesOnConstant(Instruction *II,
   return HasDeadBlocks;
 }
 
-static bool lowerConstantIntrinsics(Function &F, const TargetLibraryInfo &TLI,
-                                    DominatorTree *DT) {
+bool llvm::lowerConstantIntrinsics(Function &F, const TargetLibraryInfo &TLI,
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bjope wrote:

Oh, right. So PreISelIntrinsicLowering::lowerIntrinsics is iterating over used intrinsic functions. And then the forEachCall thing is finding out in which functions that the intrinsic is called. That way you avoid doing the RPO scanning for every function in the module.

Just a little bit weird that there is a dependency, that the switch in PreISelIntrinsicLowering::lowerIntrinsics for example may trigger on Intrinsic::objectsize, and then the calls to llvm::lowerConstantIntrinsics may lower lots of other instrinsics, and even remove dead code, as a "side-effect". There is no clear correspondance between what llvm::lowerConstantIntrinsics is doing and what is switched on in PreISelIntrinsicLowering::lowerIntrinsics.

https://github.com/llvm/llvm-project/pull/97727