[DebugInfo] Propagate DebugLoc from switch in simplifySwitchOfPowersOfTwo (llvm#165335)

A recent commit 00f5a1e modified simplifySwitchOfPowersOfTwo to
generate a branch to handle the non-power-of-2 case when appropriate,
but does not set a DebugLoc on the new branch instruction; this patch
propagates the switch's DebugLoc to the new branch, as for the other
instructions generated in the same block.

Found using llvm#107279.

Author: SLTozer

llvm/lib/Transforms/Utils/SimplifyCFG.cpp

@@ -7623,7 +7623,9 @@ static bool simplifySwitchOfPowersOfTwo(SwitchInst *SI, IRBuilder<> &Builder,
     auto *DefaultCaseBB = SI->getDefaultDest();
     BasicBlock *SplitBB = SplitBlock(OrigBB, SI, DTU);
     auto It = OrigBB->getTerminator()->getIterator();
-    BranchInst::Create(SplitBB, DefaultCaseBB, IsPow2, It);
+    auto *BI = BranchInst::Create(SplitBB, DefaultCaseBB, IsPow2, It);
+    // BI is handling the default case for SI, and so should share its DebugLoc.
+    BI->setDebugLoc(SI->getDebugLoc());
     It->eraseFromParent();
 
     addPredecessorToBlock(DefaultCaseBB, OrigBB, SplitBB);

llvm/test/Transforms/SimplifyCFG/X86/debugloc-switch-powers-of-two.ll

@@ -0,0 +1,81 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --tool ./build/bin/opt --version 6
+; RUN: opt -passes='simplifycfg<switch-to-lookup>' -simplifycfg-require-and-preserve-domtree=1 -S < %s | FileCheck %s
+;; As we replace the switch statement with a set of instructions that may more
+;; efficiently perform the conditional check, the DILocation of the switch
+;; should be propagated to all of its replacing instructions.
+
+target triple = "x86_64-unknown-linux-gnu"
+
+define i32 @switch_of_powers_two_default_reachable(i32 %arg) !dbg !5 {
+; CHECK-LABEL: define i32 @switch_of_powers_two_default_reachable(
+; CHECK-SAME: i32 [[ARG:%.*]]) !dbg [[DBG5:![0-9]+]] {
+; CHECK-NEXT:  [[ENTRY:.*]]:
+; CHECK-NEXT:    [[TMP0:%.*]] = call i32 @llvm.ctpop.i32(i32 [[ARG]]), !dbg [[DBG8:![0-9]+]]
+; CHECK-NEXT:    [[TMP1:%.*]] = icmp eq i32 [[TMP0]], 1, !dbg [[DBG8]]
+; CHECK-NEXT:    br i1 [[TMP1]], label %[[ENTRY_SPLIT:.*]], label %[[RETURN:.*]], !dbg [[DBG8]]
+; CHECK:       [[ENTRY_SPLIT]]:
+; CHECK-NEXT:    [[TMP2:%.*]] = call i32 @llvm.cttz.i32(i32 [[ARG]], i1 true), !dbg [[DBG8]]
+; CHECK-NEXT:    [[TMP3:%.*]] = icmp ult i32 [[TMP2]], 7, !dbg [[DBG8]]
+; CHECK-NEXT:    br i1 [[TMP3]], label %[[SWITCH_LOOKUP:.*]], label %[[RETURN]], !dbg [[DBG8]]
+; CHECK:       [[SWITCH_LOOKUP]]:
+; CHECK-NEXT:    [[TMP4:%.*]] = zext nneg i32 [[TMP2]] to i64, !dbg [[DBG8]]
+; CHECK-NEXT:    [[SWITCH_GEP:%.*]] = getelementptr inbounds [7 x i32], ptr @switch.table.switch_of_powers_two_default_reachable, i64 0, i64 [[TMP4]], !dbg [[DBG8]]
+; CHECK-NEXT:    [[SWITCH_LOAD:%.*]] = load i32, ptr [[SWITCH_GEP]], align 4, !dbg [[DBG8]]
+; CHECK-NEXT:    br label %[[RETURN]], !dbg [[DBG8]]
+; CHECK:       [[RETURN]]:
+; CHECK-NEXT:    [[PHI:%.*]] = phi i32 [ 5, %[[ENTRY]] ], [ 5, %[[ENTRY_SPLIT]] ], [ [[SWITCH_LOAD]], %[[SWITCH_LOOKUP]] ]
+; CHECK-NEXT:    ret i32 [[PHI]]
+;
+entry:
+  switch i32 %arg, label %default_case [
+  i32 1, label %bb1
+  i32 8, label %bb2
+  i32 16, label %bb3
+  i32 32, label %bb4
+  i32 64, label %bb5
+  ], !dbg !8
+
+default_case:                                     ; preds = %entry
+  br label %return
+
+bb1:                                              ; preds = %entry
+  br label %return
+
+bb2:                                              ; preds = %entry
+  br label %return
+
+bb3:                                              ; preds = %entry
+  br label %return
+
+bb4:                                              ; preds = %entry
+  br label %return
+
+bb5:                                              ; preds = %entry
+  br label %return
+
+return:                                           ; preds = %bb5, %bb4, %bb3, %bb2, %bb1, %default_case
+  %phi = phi i32 [ 3, %bb1 ], [ 2, %bb2 ], [ 1, %bb3 ], [ 0, %bb4 ], [ 42, %bb5 ], [ 5, %default_case ]
+  ret i32 %phi
+}
+
+!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: "debugloc-switch-powers-of-two.ll", directory: "/")
+!2 = !{i32 9}
+!3 = !{i32 1}
+!4 = !{i32 2, !"Debug Info Version", i32 3}
+!5 = distinct !DISubprogram(name: "switch_of_powers_two_default_reachable", linkageName: "switch_of_powers_two_default_reachable", scope: null, file: !1, line: 1, type: !6, scopeLine: 1, spFlags: DISPFlagDefinition | DISPFlagOptimized, unit: !0, retainedNodes: !7)
+!6 = !DISubroutineType(types: !7)
+!7 = !{}
+!8 = !DILocation(line: 1, column: 1, scope: !5)
+;.
+; CHECK: [[META0:![0-9]+]] = distinct !DICompileUnit(language: DW_LANG_C, file: [[META1:![0-9]+]], producer: "debugify", isOptimized: true, runtimeVersion: 0, emissionKind: FullDebug)
+; CHECK: [[META1]] = !DIFile(filename: "{{.*}}debugloc-switch-powers-of-two.ll", directory: {{.*}})
+; CHECK: [[DBG5]] = distinct !DISubprogram(name: "switch_of_powers_two_default_reachable", linkageName: "switch_of_powers_two_default_reachable", scope: null, file: [[META1]], line: 1, type: [[META6:![0-9]+]], scopeLine: 1, spFlags: DISPFlagDefinition | DISPFlagOptimized, unit: [[META0]], retainedNodes: [[META7:![0-9]+]])
+; CHECK: [[META6]] = !DISubroutineType(types: [[META7]])
+; CHECK: [[META7]] = !{}
+; CHECK: [[DBG8]] = !DILocation(line: 1, column: 1, scope: [[DBG5]])
+;.