[llvm] Merge sourcelocation in CSEMIRBuilder::getDominatingInstrForID. (PR #90922)

[Shubham Sandeep Rastogi via llvm-commits]

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@@ -99,6 +100,8 @@ class LegalizationArtifactCombiner {
       const LLT DstTy = MRI.getType(DstReg);
       if (isInstLegal({TargetOpcode::G_CONSTANT, {DstTy}})) {
         auto &CstVal = SrcMI->getOperand(1);
+        Builder.MergedLocation = DILocation::getMergedLocation(
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rastogishubham wrote:

@arsenm I concur with Adrian, one of the issues with the current approach is that there are multiple code paths that reach `CSEMIRBuilder::getDominatingInstrForID` so I have to clear the `MergedLocation` right after using it for the dominating instruction. If pass the DILocation through the API, we can just have a default nullptr value on it, and it doesn't change much.

https://github.com/llvm/llvm-project/pull/90922