[KeyInstr][SimplifyCFG] Remap atoms after duplication for threading (#133484)

Given the same branch condition in `a` and `c` SimplifyCFG converts:

        +> b -+
        |     v
    --> a --> c --> e -->
              |     ^
              +> d -+
into:

        +--> bcd ---+
        |           v
    --> a --> c --> e -->

Remap source atoms on instructions duplicated from `c` into `bcd`.

RFC:
https://discourse.llvm.org/t/rfc-improving-is-stmt-placement-for-better-interactive-debugging/82668

Author: OCHyams

llvm/lib/Transforms/Utils/SimplifyCFG.cpp

@@ -3590,7 +3590,7 @@ foldCondBranchOnValueKnownInPredecessorImpl(BranchInst *BI, DomTreeUpdater *DTU,
     // instructions into EdgeBB.  We know that there will be no uses of the
     // cloned instructions outside of EdgeBB.
     BasicBlock::iterator InsertPt = EdgeBB->getFirstInsertionPt();
-    DenseMap<Value *, Value *> TranslateMap; // Track translated values.
+    ValueToValueMapTy TranslateMap; // Track translated values.
     TranslateMap[Cond] = CB;
 
     // RemoveDIs: track instructions that we optimise away while folding, so
@@ -3610,11 +3610,11 @@ foldCondBranchOnValueKnownInPredecessorImpl(BranchInst *BI, DomTreeUpdater *DTU,
         N->setName(BBI->getName() + ".c");
 
       // Update operands due to translation.
-      for (Use &Op : N->operands()) {
-        DenseMap<Value *, Value *>::iterator PI = TranslateMap.find(Op);
-        if (PI != TranslateMap.end())
-          Op = PI->second;
-      }
+      // Key Instructions: Remap all the atom groups.
+      if (const DebugLoc &DL = BBI->getDebugLoc())
+        mapAtomInstance(DL, TranslateMap);
+      RemapInstruction(N, TranslateMap,
+                       RF_IgnoreMissingLocals | RF_NoModuleLevelChanges);
 
       // Check for trivial simplification.
       if (Value *V = simplifyInstruction(N, {DL, nullptr, nullptr, AC})) {

llvm/test/DebugInfo/KeyInstructions/Generic/simplifycfg-thread-phi.ll

@@ -0,0 +1,62 @@
+; RUN: opt %s -passes=simplifycfg -simplifycfg-require-and-preserve-domtree=1 -S \
+; RUN: | FileCheck %s
+
+;; Generated using:
+;;   opt -passes=debugify --debugify-atoms --debugify-level=locations \
+;;      llvm/test/Transforms/SimplifyCFG/debug-info-thread-phi.ll
+;; With unused/untested metadata nodes removed.
+
+;; Check the duplicated store gets distinct atom info in each branch.
+
+; CHECK-LABEL: @bar(
+; CHECK: if.then:
+; CHECK:   store i32 1{{.*}}, !dbg [[DBG1:!.*]]
+; CHECK: if.end.1.critedge:
+; CHECK:   store i32 1{{.*}}, !dbg [[DBG2:!.*]]
+; CHECK: [[DBG1]] = !DILocation(line: 1{{.*}}, atomGroup: 1
+; CHECK: [[DBG2]] = !DILocation(line: 1{{.*}}, atomGroup: 2
+
+define void @bar(i32 %aa) !dbg !5 {
+entry:
+  %aa.addr = alloca i32, align 4
+  %bb = alloca i32, align 4
+  store i32 %aa, ptr %aa.addr, align 4
+  store i32 0, ptr %bb, align 4
+  %tobool = icmp ne i32 %aa, 0
+  br i1 %tobool, label %if.then, label %if.end
+
+if.then:                                          ; preds = %entry
+  call void @foo()
+  br label %if.end
+
+if.end:                                           ; preds = %if.then, %entry
+  store i32 1, ptr %bb, align 4, !dbg !8
+  br i1 %tobool, label %if.then.1, label %if.end.1
+
+if.then.1:                                        ; preds = %if.end
+  call void @foo()
+  br label %if.end.1
+
+if.end.1:                                         ; preds = %if.then.1, %if.end
+  store i32 2, ptr %bb, align 4
+  br label %for.end
+
+for.end:                                          ; preds = %if.end.1
+  ret void
+}
+
+declare void @foo()
+
+!llvm.dbg.cu = !{!0}
+!llvm.debugify = !{!2, !3}
+!llvm.module.flags = !{!4}
+
+!0 = distinct !DICompileUnit(language: DW_LANG_C, file: !1, producer: "debugify", isOptimized: true, runtimeVersion: 0, emissionKind: FullDebug)
+!1 = !DIFile(filename: "llvm/test/Transforms/SimplifyCFG/debug-info-thread-phi.ll", directory: "/")
+!2 = !{i32 15}
+!3 = !{i32 0}
+!4 = !{i32 2, !"Debug Info Version", i32 3}
+!5 = distinct !DISubprogram(name: "bar", linkageName: "bar", scope: null, file: !1, line: 1, type: !6, scopeLine: 1, spFlags: DISPFlagDefinition | DISPFlagOptimized, unit: !0)
+!6 = !DISubroutineType(types: !7)
+!7 = !{}
+!8 = !DILocation(line: 1, column: 1, scope: !5, atomGroup: 1, atomRank: 1)