Index: include/llvm/Transforms/Utils/Local.h =================================================================== --- include/llvm/Transforms/Utils/Local.h +++ include/llvm/Transforms/Utils/Local.h @@ -446,6 +446,15 @@ /// Remove the debug intrinsic instructions for the given instruction. void dropDebugUsers(Instruction &I); +/// Hoist all of the instructions in the \p IfBlock to the dominant block +/// \p DomBlock, by moving its instructions to the insertion point \p InsertPt. +/// +/// The moved instructions receive the insertion point debug location values +/// (DILocations) and their debug intrinsic instructions (dbg.values) are +/// removed. +void hoistAllInstructionsInto(BasicBlock *DomBlock,Instruction *InsertPt, + BasicBlock *IfBlock); + //===----------------------------------------------------------------------===// // Intrinsic pattern matching // Index: lib/Transforms/Utils/Local.cpp =================================================================== --- lib/Transforms/Utils/Local.cpp +++ lib/Transforms/Utils/Local.cpp @@ -2529,6 +2529,35 @@ DII->eraseFromParent(); } +void llvm::hoistAllInstructionsInto(BasicBlock *DomBlock,Instruction *InsertPt, + BasicBlock *IfBlock) { + // Since we are moving the instructions out of its basic block, we do not + // retain their original debug locations (DILocations) and debug intrinsic + // instructions (dbg.values). + // + // Doing so would degrade the debugging experience and adversely affect the + // accuracy of profiling information: + // - Moving debug locations around degrades single-stepping and profiling. + // - Moving dbg.values around makes variable updates appear re-ordered in a + // debug session. + // + // TODO: Extend llvm.dbg.value to take more than one SSA Value (PR39141) to + // encode predicated DIExpressions that yield different results on different + // code paths. + // + // Currently, when hoisting the instructions, we take the following actions: + // - Remove their dbg.values. + // - Set their debug locations to the values from the insertion point. + for (auto &I : *IfBlock) { + I.dropUnknownNonDebugMetadata(); + dropDebugUsers(I); + I.setDebugLoc(InsertPt->getDebugLoc()); + } + DomBlock->getInstList().splice(InsertPt->getIterator(), + IfBlock->getInstList(), IfBlock->begin(), + IfBlock->getTerminator()->getIterator()); +} + namespace { /// A potential constituent of a bitreverse or bswap expression. See Index: lib/Transforms/Utils/SimplifyCFG.cpp =================================================================== --- lib/Transforms/Utils/SimplifyCFG.cpp +++ lib/Transforms/Utils/SimplifyCFG.cpp @@ -2375,24 +2375,10 @@ // Move all 'aggressive' instructions, which are defined in the // conditional parts of the if's up to the dominating block. - if (IfBlock1) { - for (auto &I : *IfBlock1) { - I.dropUnknownNonDebugMetadata(); - dropDebugUsers(I); - } - DomBlock->getInstList().splice(InsertPt->getIterator(), - IfBlock1->getInstList(), IfBlock1->begin(), - IfBlock1->getTerminator()->getIterator()); - } - if (IfBlock2) { - for (auto &I : *IfBlock2) { - I.dropUnknownNonDebugMetadata(); - dropDebugUsers(I); - } - DomBlock->getInstList().splice(InsertPt->getIterator(), - IfBlock2->getInstList(), IfBlock2->begin(), - IfBlock2->getTerminator()->getIterator()); - } + if (IfBlock1) + hoistAllInstructionsInto(DomBlock, InsertPt, IfBlock1); + if (IfBlock2) + hoistAllInstructionsInto(DomBlock, InsertPt, IfBlock2); while (PHINode *PN = dyn_cast(BB->begin())) { // Change the PHI node into a select instruction. Index: test/CodeGen/X86/pr38762.ll =================================================================== --- test/CodeGen/X86/pr38762.ll +++ test/CodeGen/X86/pr38762.ll @@ -0,0 +1,105 @@ +; RUN: opt < %s -S -simplifycfg | FileCheck %s + +; Note: This patch is a complement to pr38763. +; +; When SimplifyCFG changes the PHI node into a select instruction, the debug +; information becomes ambiguous. It causes the debugger to display unreached +; lines and invalid variable values. +; +; When in the debugger, on the line "if (read1 > 3)", and we step from the +; 'if' condition, onto the addition, then back to the 'if' again, which is +; misleading because that addition doesn't really "happen" (it's speculated). + +; IR generated with: +; clang -S -g -gno-column-info -O2 -emit-llvm pr38762.cpp -o pr38762.ll -mllvm -opt-bisect-limit=10 + +; // pr38762.cpp +; int main() { +; volatile int foo = 0; +; int read1 = foo; +; int brains = foo; +; +; if (read1 > 3) { +; brains *= 2; +; brains += 1; +; } +; +; return brains; +; } + +; Change the debug locations associated with the PHI nodes being promoted, to +; the debug locations from the insertion point in the dominant block. + +; CHECK-LABEL: entry +; CHECK: %cmp = icmp sgt i32 %foo.0., 3, !dbg !18 +; CHECK: %mul = shl nsw i32 %foo.0.5, 1, !dbg !20 +; CHECK-NOT: call void @llvm.dbg.value(metadata i32 %mul, metadata !15, metadata !DIExpression()), !dbg !25 +; CHECK: %add = or i32 %mul, 1, !dbg !20 +; CHECK-NOT: call void @llvm.dbg.value(metadata i32 %add, metadata !15, metadata !DIExpression()), !dbg !25 +; CHECK: %brains.0 = select i1 %cmp, i32 %add, i32 %foo.0.5, !dbg !20 + +; ModuleID = 'pr38762.cpp' +source_filename = "pr38762.cpp" +target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128" +target triple = "x86_64-pc-linux-gnu" + +; Function Attrs: norecurse nounwind uwtable +define dso_local i32 @main() local_unnamed_addr #0 !dbg !7 { +entry: + %foo = alloca i32, align 4 + %foo.0..sroa_cast = bitcast i32* %foo to i8* + store volatile i32 0, i32* %foo, align 4, !tbaa !18 + %foo.0. = load volatile i32, i32* %foo, align 4, !tbaa !18 + %foo.0.5 = load volatile i32, i32* %foo, align 4, !tbaa !18 + call void @llvm.dbg.value(metadata i32 %foo.0.5, metadata !15, metadata !DIExpression()), !dbg !25 + %cmp = icmp sgt i32 %foo.0., 3, !dbg !26 + br i1 %cmp, label %if.then, label %if.end, !dbg !28 + +if.then: ; preds = %entry + %mul = shl nsw i32 %foo.0.5, 1, !dbg !29 + call void @llvm.dbg.value(metadata i32 %mul, metadata !15, metadata !DIExpression()), !dbg !25 + %add = or i32 %mul, 1, !dbg !31 + call void @llvm.dbg.value(metadata i32 %add, metadata !15, metadata !DIExpression()), !dbg !25 + br label %if.end, !dbg !32 + +if.end: ; preds = %if.then, %entry + %brains.0 = phi i32 [ %add, %if.then ], [ %foo.0.5, %entry ], !dbg !33 + call void @llvm.dbg.value(metadata i32 %brains.0, metadata !15, metadata !DIExpression()), !dbg !25 + ret i32 %brains.0, !dbg !35 +} + +declare void @llvm.dbg.value(metadata, metadata, metadata) #2 + +!llvm.dbg.cu = !{!0} +!llvm.module.flags = !{!3, !4, !5} +!llvm.ident = !{!6} + +!0 = distinct !DICompileUnit(language: DW_LANG_C_plus_plus, file: !1, producer: "clang version 8.0.0 (trunk 343753)", isOptimized: true, runtimeVersion: 0, emissionKind: FullDebug, enums: !2, nameTableKind: None) +!1 = !DIFile(filename: "pr38762.cpp", directory: ".") +!2 = !{} +!3 = !{i32 2, !"Dwarf Version", i32 4} +!4 = !{i32 2, !"Debug Info Version", i32 3} +!5 = !{i32 1, !"wchar_size", i32 4} +!6 = !{!"clang version 8.0.0 (trunk 343753)"} +!7 = distinct !DISubprogram(name: "main", scope: !1, file: !1, line: 1, type: !8, isLocal: false, isDefinition: true, scopeLine: 1, flags: DIFlagPrototyped, isOptimized: true, unit: !0, retainedNodes: !11) +!8 = !DISubroutineType(types: !9) +!9 = !{!10} +!10 = !DIBasicType(name: "int", size: 32, encoding: DW_ATE_signed) +!11 = !{!15} +!13 = !DIDerivedType(tag: DW_TAG_volatile_type, baseType: !10) +!15 = !DILocalVariable(name: "brains", scope: !7, file: !1, line: 4, type: !10) +!18 = !{!19, !19, i64 0} +!19 = !{!"int", !20, i64 0} +!20 = !{!"omnipotent char", !21, i64 0} +!21 = !{!"Simple C++ TBAA"} +!25 = !DILocation(line: 4, scope: !7) +!26 = !DILocation(line: 6, scope: !27) +!27 = distinct !DILexicalBlock(scope: !7, file: !1, line: 6) +!28 = !DILocation(line: 6, scope: !7) +!29 = !DILocation(line: 7, scope: !30) +!30 = distinct !DILexicalBlock(scope: !27, file: !1, line: 6) +!31 = !DILocation(line: 8, scope: !30) +!32 = !DILocation(line: 9, scope: !30) +!33 = !DILocation(line: 0, scope: !7) +!34 = !DILocation(line: 12, scope: !7) +!35 = !DILocation(line: 11, scope: !7) Index: test/CodeGen/X86/pr38763.ll =================================================================== --- test/CodeGen/X86/pr38763.ll +++ test/CodeGen/X86/pr38763.ll @@ -30,10 +30,10 @@ ; branches, as they becomes ambiguous. ; CHECK-LABEL: entry -; CHECK: %cmp = icmp eq i32 %foo.0., 4 -; CHECK: %add = add nsw i32 %foo.0.4, 2, !dbg !18 +; CHECK: %cmp = icmp eq i32 %foo.0., 4, !dbg !18 +; CHECK: %add = add nsw i32 %foo.0.4, 2, !dbg !20 ; CHECK-NOT: @llvm.dbg.value(metadata i32 %add -; CHECK: %sub = add nsw i32 %foo.0.4, -2, !dbg !21 +; CHECK: %sub = add nsw i32 %foo.0.4, -2, !dbg !20 ; CHECK-NOT: @llvm.dbg.value(metadata i32 %sub ; CHECK: %result.0 = select i1 %cmp, i32 %add, i32 %sub ; CHECK: call void @llvm.dbg.value(metadata i32 %result.0, metadata !12, metadata !DIExpression()), !dbg !17 @@ -52,8 +52,8 @@ %foo.0. = load volatile i32, i32* %foo, align 4 %foo.0.4 = load volatile i32, i32* %foo, align 4 call void @llvm.dbg.value(metadata i32 0, metadata !16, metadata !DIExpression()), !dbg !27 - %cmp = icmp eq i32 %foo.0., 4 - br i1 %cmp, label %if.then, label %if.else + %cmp = icmp eq i32 %foo.0., 4, !dbg !28 + br i1 %cmp, label %if.then, label %if.else, !dbg !30 if.then: ; preds = %entry %add = add nsw i32 %foo.0.4, 2, !dbg !31 @@ -96,7 +96,9 @@ !21 = !{!"omnipotent char", !22, i64 0} !22 = !{!"Simple C++ TBAA"} !27 = !DILocation(line: 6, column: 7, scope: !7) +!28 = !DILocation(line: 7, column: 12, scope: !29) !29 = distinct !DILexicalBlock(scope: !7, file: !1, line: 7, column: 7) +!30 = !DILocation(line: 7, column: 7, scope: !7) !31 = !DILocation(line: 8, column: 20, scope: !32) !32 = distinct !DILexicalBlock(scope: !29, file: !1, line: 7, column: 18) !34 = !DILocation(line: 10, column: 20, scope: !35)