[DebugInfo][InstCombine] Do not overwrite prior DILocation for new Insts

llvm/lib/Transforms/InstCombine/InstructionCombining.cpp

@@ -5170,8 +5170,13 @@ bool InstCombinerImpl::run() {
         LLVM_DEBUG(dbgs() << "IC: Old = " << *I << '\n'
                           << "    New = " << *Result << '\n');
 
-        Result->copyMetadata(*I,
-                             {LLVMContext::MD_dbg, LLVMContext::MD_annotation});
+        // We copy the old instruction's DebugLoc to the new instruction, unless
+        // InstCombine already assigned a DebugLoc to it, in which case we
+        // should trust the more specifically selected DebugLoc.
+        if (!Result->getDebugLoc())
+          Result->setDebugLoc(I->getDebugLoc());
+        // We also copy annotation metadata to the new instruction.
+        Result->copyMetadata(*I, LLVMContext::MD_annotation);
         // Everything uses the new instruction now.
         I->replaceAllUsesWith(Result);
 

llvm/test/Transforms/InstCombine/new-inst-dbgloc-overwrite.ll

@@ -0,0 +1,77 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --check-globals smart
+;; Tests that when InstCombine sets a DILocation on the new instruction when it
+;; is created, we do not try to overwrite that DILocation when we later insert
+;; the new instruction.
+;; In this test, InstCombine replaces two loads joined by a PHI into a PHI of
+;; the addresses followed by a load, and gives the new load a merge of the two
+;; incoming load DILocations. This test verifies that the new load keeps that
+;; DILocation, and doesn't have it overwritten by the DILocation of the original
+;; PHI. It will, however, receive the !annotation attached to the original PHI.
+; RUN: opt < %s -passes=instcombine -S | FileCheck %s
+
+define void @test(ptr %xfA, ptr %xfB, i1 %cmp5) {
+; CHECK-LABEL: @test(
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    br i1 [[CMP5:%.*]], label [[IF_ELSE:%.*]], label [[IF_THEN6:%.*]]
+; CHECK:       if.then6:
+; CHECK-NEXT:    br label [[IF_END11:%.*]]
+; CHECK:       if.else:
+; CHECK-NEXT:    br label [[IF_END11]]
+; CHECK:       if.end11:
+; CHECK-NEXT:    [[XFA_PN:%.*]] = phi ptr [ [[XFA:%.*]], [[IF_ELSE]] ], [ [[XFB:%.*]], [[IF_THEN6]] ]
+; CHECK-NEXT:    [[XF1_SROA_8_0_IN:%.*]] = getelementptr i8, ptr [[XFA_PN]], i64 4
+; CHECK-NEXT:    [[XF1_SROA_8_0:%.*]] = load float, ptr [[XF1_SROA_8_0_IN]], align 4, !dbg [[DBG3:![0-9]+]], !annotation [[META7:![0-9]+]]
+; CHECK-NEXT:    [[CMP_I:%.*]] = fcmp ugt float [[XF1_SROA_8_0]], 0.000000e+00
+; CHECK-NEXT:    br i1 [[CMP_I]], label [[IF_END_I:%.*]], label [[IF_THEN_I:%.*]]
+; CHECK:       if.then.i:
+; CHECK-NEXT:    br label [[IF_END_I]]
+; CHECK:       if.end.i:
+; CHECK-NEXT:    ret void
+;
+entry:
+  br i1 %cmp5, label %if.else, label %if.then6
+
+if.then6:                                         ; preds = %entry
+  %xf1.sroa.8.0.xfB.sroa_idx = getelementptr i8, ptr %xfB, i64 4
+  %xf1.sroa.8.0.copyload = load float, ptr %xf1.sroa.8.0.xfB.sroa_idx, align 4, !dbg !3
+  br label %if.end11
+
+if.else:                                          ; preds = %entry
+  %xf1.sroa.8.0.xfA.sroa_idx = getelementptr i8, ptr %xfA, i64 4
+  %xf1.sroa.8.0.copyload494 = load float, ptr %xf1.sroa.8.0.xfA.sroa_idx, align 4, !dbg !7
+  br label %if.end11
+
+if.end11:                                         ; preds = %if.else, %if.then6
+  %xf1.sroa.8.0 = phi float [ %xf1.sroa.8.0.copyload494, %if.else ], [ %xf1.sroa.8.0.copyload, %if.then6 ], !dbg !8, !annotation !9
+  %cmp.i = fcmp ugt float %xf1.sroa.8.0, 0.000000e+00
+  br i1 %cmp.i, label %if.end.i, label %if.then.i
+
+if.then.i:                                        ; preds = %if.end11
+  br label %if.end.i
+
+if.end.i:                                         ; preds = %if.then.i, %if.end11
+  ret void
+}
+
+!llvm.dbg.cu = !{!0}
+!llvm.module.flags = !{!2}
+
+!0 = distinct !DICompileUnit(language: DW_LANG_C_plus_plus, file: !1, producer: "clang version 20.0.0git", isOptimized: true, runtimeVersion: 0, emissionKind: FullDebug)
+!1 = !DIFile(filename: "test.cpp", directory: "/tmp")
+!2 = !{i32 2, !"Debug Info Version", i32 3}
+!3 = !DILocation(line: 13, column: 12, scope: !4)
+!4 = distinct !DISubprogram(name: "operator=", linkageName: "_ZN11btMatrix3x3aSERKS_", scope: null, file: !1, line: 61, type: !5, scopeLine: 62, spFlags: DISPFlagDefinition, unit: !0, retainedNodes: !6)
+!5 = distinct !DISubroutineType(types: !6)
+!6 = !{}
+!7 = !DILocation(line: 13, column: 15, scope: !4)
+!8 = !DILocation(line: 100, scope: !4)
+!9 = !{!"Test String"}
+;.
+; CHECK: [[META0:![0-9]+]] = distinct !DICompileUnit(language: DW_LANG_C_plus_plus, file: [[META1:![0-9]+]], producer: "{{.*}}clang version {{.*}}", isOptimized: true, runtimeVersion: 0, emissionKind: FullDebug)
+; CHECK: [[META1]] = !DIFile(filename: "test.cpp", directory: {{.*}})
+; CHECK: [[DBG3]] = !DILocation(line: 13, scope: [[META4:![0-9]+]])
+; CHECK: [[META4]] = distinct !DISubprogram(name: "operator=", linkageName: "_ZN11btMatrix3x3aSERKS_", scope: null, file: [[META1]], line: 61, type: [[META5:![0-9]+]], scopeLine: 62, spFlags: DISPFlagDefinition, unit: [[META0]], retainedNodes: [[META6:![0-9]+]])
+; CHECK: [[META5]] = distinct !DISubroutineType(types: [[META6]])
+; CHECK: [[META6]] = !{}
+; CHECK: [[META7]] = !{!"Test String"}
+;.