Fix #135736: salvage debug values with replaced constants

Author: Apochens

llvm/lib/Transforms/Scalar/ConstraintElimination.cpp

@@ -25,6 +25,7 @@
 #include "llvm/Analysis/ValueTracking.h"
 #include "llvm/IR/DataLayout.h"
 #include "llvm/IR/Dominators.h"
+#include "llvm/IR/DebugInfo.h"
 #include "llvm/IR/Function.h"
 #include "llvm/IR/IRBuilder.h"
 #include "llvm/IR/InstrTypes.h"
@@ -1454,8 +1455,20 @@ static bool checkAndReplaceCondition(
       return ShouldReplace;
     });
     NumCondsRemoved++;
-    if (Cmp->use_empty())
+    if (Cmp->use_empty()) {
+      SmallVector<DbgVariableIntrinsic *> DbgUsers;
+      SmallVector<DbgVariableRecord *> DVRUsers;
+      findDbgUsers(DbgUsers, Cmp, &DVRUsers);
+      
+      for (auto *DVR: DVRUsers) {
+        auto *DTN = DT.getNode(DVR->getParent());
+        if (!DTN || DTN->getDFSNumIn() < NumIn || DTN->getDFSNumOut() > NumOut)
+          continue;
+        DVR->replaceVariableLocationOp(Cmp, ConstantC);
+      }
+
       ToRemove.push_back(Cmp);
+    }
     return Changed;
   };
 

llvm/test/Transforms/ConstraintElimination/salvage-dbg-values-replaced-by-constant.ll

@@ -0,0 +1,80 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 5
+; RUN: opt < %s -passes=constraint-elimination -S | FileCheck %s
+
+; Check that checkAndReplaceCondition() salvages the debug value information after replacing
+; the conditions (%t.1 in this test) with the speculated constants (GitHub Issue #135736).
+
+define i1 @test_and_ule(i4 %x, i4 %y, i4 %z) !dbg !5 {
+; CHECK-LABEL: define i1 @test_and_ule(
+; CHECK-SAME: i4 [[X:%.*]], i4 [[Y:%.*]], i4 [[Z:%.*]]) !dbg [[DBG5:![0-9]+]] {
+; CHECK-NEXT:  [[ENTRY:.*:]]
+; CHECK-NEXT:    [[C_1:%.*]] = icmp ule i4 [[X]], [[Y]], !dbg [[DBG11:![0-9]+]]
+; CHECK-NEXT:    [[C_2:%.*]] = icmp ule i4 [[Y]], [[Z]], !dbg [[DBG12:![0-9]+]]
+; CHECK-NEXT:    [[AND:%.*]] = and i1 [[C_1]], [[C_2]], !dbg [[DBG13:![0-9]+]]
+; CHECK-NEXT:    br i1 [[AND]], label %[[THEN:.*]], label %[[EXIT:.*]], !dbg [[DBG14:![0-9]+]]
+; CHECK:       [[THEN]]:
+; CHECK-NEXT:      #dbg_value(i1 true, [[META9:![0-9]+]], !DIExpression(), [[META15:![0-9]+]])
+; CHECK-NEXT:    [[R_1:%.*]] = xor i1 true, true, !dbg [[DBG16:![0-9]+]]
+; CHECK-NEXT:    br label %[[EXIT]]
+; CHECK:       [[EXIT]]:
+; CHECK-NEXT:      #dbg_value(i1 poison, [[META17:![0-9]+]], !DIExpression(), [[META15]])
+; CHECK-NEXT:    ret i1 true, !dbg [[DBG18:![0-9]+]]
+;
+entry:
+  %c.1 = icmp ule i4 %x, %y, !dbg !11
+  %c.2 = icmp ule i4 %y, %z, !dbg !12
+  %t.1 = icmp ule i4 %x, %z, !dbg !13
+  %and = and i1 %c.1, %c.2, !dbg !14
+  br i1 %and, label %then, label %exit, !dbg !15
+
+then:                                              ; preds = %entry
+  #dbg_value(i1 %t.1, !9, !DIExpression(), !13)
+  %r.1 = xor i1 %t.1, %t.1, !dbg !16
+  br label %exit
+
+exit:                                             ; preds = %bb1, %entry
+  #dbg_value(i1 %t.1, !17, !DIExpression(), !13)
+  ret i1 true, !dbg !18
+}
+
+!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: "temp.ll", directory: "/")
+!2 = !{i32 20}
+!3 = !{i32 17}
+!4 = !{i32 2, !"Debug Info Version", i32 3}
+!5 = distinct !DISubprogram(name: "test_and_ule", linkageName: "test_and_ule", scope: null, file: !1, line: 1, type: !6, scopeLine: 1, spFlags: DISPFlagDefinition | DISPFlagOptimized, unit: !0, retainedNodes: !8)
+!6 = !DISubroutineType(types: !7)
+!7 = !{}
+!8 = !{!9}
+!9 = !DILocalVariable(name: "4", scope: !5, file: !1, line: 5, type: !10)
+!10 = !DIBasicType(name: "ty8", size: 8, encoding: DW_ATE_unsigned)
+!11 = !DILocation(line: 1, column: 1, scope: !5)
+!12 = !DILocation(line: 2, column: 1, scope: !5)
+!13 = !DILocation(line: 5, column: 1, scope: !5)
+!14 = !DILocation(line: 3, column: 1, scope: !5)
+!15 = !DILocation(line: 4, column: 1, scope: !5)
+!16 = !DILocation(line: 7, column: 1, scope: !5)
+!17 = !DILocalVariable(name: "6", scope: !5, file: !1, line: 7, type: !10)
+!18 = !DILocation(line: 20, 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: "temp.ll", directory: {{.*}})
+; CHECK: [[DBG5]] = distinct !DISubprogram(name: "test_and_ule", linkageName: "test_and_ule", scope: null, file: [[META1]], line: 1, type: [[META6:![0-9]+]], scopeLine: 1, spFlags: DISPFlagDefinition | DISPFlagOptimized, unit: [[META0]], retainedNodes: [[META8:![0-9]+]])
+; CHECK: [[META6]] = !DISubroutineType(types: [[META7:![0-9]+]])
+; CHECK: [[META7]] = !{}
+; CHECK: [[META8]] = !{[[META9]]}
+; CHECK: [[META9]] = !DILocalVariable(name: "4", scope: [[DBG5]], file: [[META1]], line: 5, type: [[META10:![0-9]+]])
+; CHECK: [[META10]] = !DIBasicType(name: "ty8", size: 8, encoding: DW_ATE_unsigned)
+; CHECK: [[DBG11]] = !DILocation(line: 1, column: 1, scope: [[DBG5]])
+; CHECK: [[DBG12]] = !DILocation(line: 2, column: 1, scope: [[DBG5]])
+; CHECK: [[DBG13]] = !DILocation(line: 3, column: 1, scope: [[DBG5]])
+; CHECK: [[DBG14]] = !DILocation(line: 4, column: 1, scope: [[DBG5]])
+; CHECK: [[META15]] = !DILocation(line: 5, column: 1, scope: [[DBG5]])
+; CHECK: [[DBG16]] = !DILocation(line: 7, column: 1, scope: [[DBG5]])
+; CHECK: [[META17]] = !DILocalVariable(name: "6", scope: [[DBG5]], file: [[META1]], line: 7, type: [[META10]])
+; CHECK: [[DBG18]] = !DILocation(line: 20, column: 1, scope: [[DBG5]])
+;.