[llvm] [DirectX] Add support to lower LLVM intrinsics ceil, cos, fabs, floor and smax to DXIL Ops. (PR #78767)

[S. Bharadwaj Yadavalli via llvm-commits]

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@@ -28,6 +28,12 @@ void initializeDXILPrepareModulePass(PassRegistry &);
 /// Pass to convert modules into DXIL-compatable modules
 ModulePass *createDXILPrepareModulePass();
 
+/// Initializer for DXIL strength reduce
+void initializeDXILStrengthReducePass(PassRegistry &);
+
+/// Pass to reduce strength during lowering into DXIL-compatable modules
+ModulePass *createDXILStrengthReducePass();
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bharadwajy wrote:

This pass is introduced to rewrite intrinsics such as `llvm.abs.*` (integer abs) with no corresponding DXIL intrinsic (AFAIK). For example, `llvm.abs` is rewritten in this pass as a combination of `sub` (LLVM instruction) and `smax` (LLVM intrinsic) - as done in DXC. 

https://github.com/llvm/llvm-project/pull/78767