When instructions are hoisted out of loops by MachineLICM, remove their debug loc.

This prevents erratic stepping behavior as well as incorrect source attribution
for sample profiling.

Reviewers: dblakie

Subscribers: llvm-commit

Differential Revision: https://reviews.llvm.org/D27290

llvm-svn: 288442

llvm/lib/CodeGen/MachineLICM.cpp

@@ -1336,6 +1336,11 @@ bool MachineLICM::Hoist(MachineInstr *MI, MachineBasicBlock *Preheader) {
     // Otherwise, splice the instruction to the preheader.
     Preheader->splice(Preheader->getFirstTerminator(),MI->getParent(),MI);
 
+    // Since we are moving the instruction out of its basic block, we do not
+    // retain its debug location. Doing so would degrade the debugging 
+    // experience and adversely affect the accuracy of profiling information.
+    MI->setDebugLoc(DebugLoc());
+
     // Update register pressure for BBs from header to this block.
     UpdateBackTraceRegPressure(MI);
 

llvm/test/CodeGen/ARM/debug-info-branch-folding.ll

@@ -3,11 +3,12 @@ target datalayout = "e-p:32:32:32-i1:8:32-i8:8:32-i16:16:32-i32:32:32-i64:32:32-
 target triple = "thumbv7-apple-macosx10.6.7"
 
 ;CHECK: 	vadd.f32	q4, q8, q8
-;CHECK-NEXT: Ltmp1
+;CHECK:         LBB0_1:
-;CHECK-NEXT: LBB0_1
+;CHECK-NOT:     beq LBB0_1
 
-;CHECK:@DEBUG_VALUE: x <- %Q4{{$}}
+;CHECK:         @DEBUG_VALUE: x <- %Q4{{$}}
-;CHECK-NEXT:@DEBUG_VALUE: y <- %Q4{{$}}
+;CHECK-NEXT:    @DEBUG_VALUE: y <- %Q4{{$}}
+;CHECK:         beq LBB0_1
 
 
 @.str = external constant [13 x i8]

llvm/test/DebugInfo/MIR/X86/mlicm-hoist.mir

@@ -0,0 +1,141 @@
+--- |
+  ; RUN: llc -run-pass=machinelicm -o - %s | FileCheck %s
+  ; Line numbers should not be retained when loop invariant instructions are hoisted.
+  ; Doing so causes poor stepping bevavior.
+  ;
+  ; Created from:
+  ; int x;
+  ; void Process(const unsigned int *p)
+  ; {
+  ;    while (1)
+  ;      x = *p++;
+  ; }
+  ;
+  ; with clang -emit-llvm -S -O2 -g -o t.ll t.c
+  ;      llc -relocation-model=pic -stop-after=machine-combine -O2 t.ll -o t.mir
+  ;
+  ; We check that when the machine loop invariant pass hoists instructions
+  ; out of a loop the debug information is not retained.
+  ;
+  ; CHECK-LABEL:  bb.0.entry:
+  ; CHECK:        MOV64rm %rip, 1, _, target-flags(x86-gotpcrel) @x, _ :: (load 8 from got)
+  ; CHECK-LABEL:  bb.1.while.body:
+  ;
+  ; ModuleID = 'tx.ll'
+  source_filename = "t.c"
+  target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
+  target triple = "x86_64-unknown-linux-gnu"
+
+  @x = common local_unnamed_addr global i32 0, align 4, !dbg !0
+
+  ; Function Attrs: noreturn nounwind uwtable
+  define void @Process(i32* nocapture readonly %p) local_unnamed_addr #0 !dbg !9 {
+  entry:
+    tail call void @llvm.dbg.value(metadata i32* %p, i64 0, metadata !16, metadata !17), !dbg !18
+    br label %while.body, !dbg !19
+
+  while.body:                                       ; preds = %while.body, %entry
+    %p.addr.0 = phi i32* [ %p, %entry ], [ %incdec.ptr, %while.body ]
+    tail call void @llvm.dbg.value(metadata i32* %p.addr.0, i64 0, metadata !16, metadata !17), !dbg !18
+    %incdec.ptr = getelementptr inbounds i32, i32* %p.addr.0, i64 1, !dbg !20
+    tail call void @llvm.dbg.value(metadata i32* %incdec.ptr, i64 0, metadata !16, metadata !17), !dbg !18
+    %0 = load i32, i32* %p.addr.0, align 4, !dbg !21, !tbaa !22
+    store i32 %0, i32* @x, align 4, !dbg !26, !tbaa !22
+    br label %while.body, !dbg !27, !llvm.loop !29
+  }
+
+  ; Function Attrs: nounwind readnone
+  declare void @llvm.dbg.value(metadata, i64, metadata, metadata) #1
+
+  attributes #0 = { noreturn nounwind uwtable "correctly-rounded-divide-sqrt-fp-math"="false" "disable-tail-calls"="false" "less-precise-fpmad"="false" "no-frame-pointer-elim"="false" "no-infs-fp-math"="false" "no-jump-tables"="false" "no-nans-fp-math"="false" "no-signed-zeros-fp-math"="false" "no-trapping-math"="false" "stack-protector-buffer-size"="8" "target-cpu"="x86-64" "target-features"="+fxsr,+mmx,+sse,+sse2,+x87" "unsafe-fp-math"="false" "use-soft-float"="false" }
+  attributes #1 = { nounwind readnone }
+  attributes #2 = { nounwind }
+
+  !llvm.dbg.cu = !{!1}
+  !llvm.module.flags = !{!6, !7}
+  !llvm.ident = !{!8}
+
+  !0 = distinct !DIGlobalVariable(name: "x", scope: !1, file: !2, line: 1, type: !5, isLocal: false, isDefinition: true)
+  !1 = distinct !DICompileUnit(language: DW_LANG_C99, file: !2, producer: "clang version 4.0.0 ", isOptimized: true, runtimeVersion: 0, emissionKind: FullDebug, enums: !3, globals: !4)
+  !2 = !DIFile(filename: "t.c", directory: "/home/test")
+  !3 = !{}
+  !4 = !{!0}
+  !5 = !DIBasicType(name: "int", size: 32, encoding: DW_ATE_signed)
+  !6 = !{i32 2, !"Dwarf Version", i32 4}
+  !7 = !{i32 2, !"Debug Info Version", i32 3}
+  !8 = !{!"clang version 4.0.0 "}
+  !9 = distinct !DISubprogram(name: "Process", scope: !2, file: !2, line: 2, type: !10, isLocal: false, isDefinition: true, scopeLine: 3, flags: DIFlagPrototyped, isOptimized: true, unit: !1, variables: !15)
+  !10 = !DISubroutineType(types: !11)
+  !11 = !{null, !12}
+  !12 = !DIDerivedType(tag: DW_TAG_pointer_type, baseType: !13, size: 64)
+  !13 = !DIDerivedType(tag: DW_TAG_const_type, baseType: !14)
+  !14 = !DIBasicType(name: "unsigned int", size: 32, encoding: DW_ATE_unsigned)
+  !15 = !{!16}
+  !16 = !DILocalVariable(name: "p", arg: 1, scope: !9, file: !2, line: 2, type: !12)
+  !17 = !DIExpression()
+  !18 = !DILocation(line: 2, column: 34, scope: !9)
+  !19 = !DILocation(line: 4, column: 3, scope: !9)
+  !20 = !DILocation(line: 5, column: 11, scope: !9)
+  !21 = !DILocation(line: 5, column: 9, scope: !9)
+  !22 = !{!23, !23, i64 0}
+  !23 = !{!"int", !24, i64 0}
+  !24 = !{!"omnipotent char", !25, i64 0}
+  !25 = !{!"Simple C/C++ TBAA"}
+  !26 = !DILocation(line: 5, column: 7, scope: !9)
+  !27 = !DILocation(line: 4, column: 3, scope: !28)
+  !28 = !DILexicalBlockFile(scope: !9, file: !2, discriminator: 1)
+  !29 = distinct !{!29, !19, !20}
+
+...
+---
+name:            Process
+alignment:       4
+exposesReturnsTwice: false
+legalized:       false
+regBankSelected: false
+selected:        false
+tracksRegLiveness: true
+registers:
+  - { id: 0, class: gr64 }
+  - { id: 1, class: gr64 }
+  - { id: 2, class: gr64 }
+  - { id: 3, class: gr32 }
+  - { id: 4, class: gr64 }
+liveins:
+  - { reg: '%rdi', virtual-reg: '%2' }
+frameInfo:
+  isFrameAddressTaken: false
+  isReturnAddressTaken: false
+  hasStackMap:     false
+  hasPatchPoint:   false
+  stackSize:       0
+  offsetAdjustment: 0
+  maxAlignment:    0
+  adjustsStack:    false
+  hasCalls:        false
+  maxCallFrameSize: 0
+  hasOpaqueSPAdjustment: false
+  hasVAStart:      false
+  hasMustTailInVarArgFunc: false
+body:             |
+  bb.0.entry:
+    successors: %bb.1.while.body(0x80000000)
+    liveins: %rdi
+
+    DBG_VALUE debug-use %rdi, debug-use _, !16, !17, debug-location !18
+    %2 = COPY %rdi
+    DBG_VALUE debug-use %2, debug-use _, !16, !17, debug-location !18
+
+  bb.1.while.body:
+    successors: %bb.1.while.body(0x80000000)
+
+    %0 = PHI %2, %bb.0.entry, %1, %bb.1.while.body
+    DBG_VALUE debug-use %0, debug-use _, !16, !17, debug-location !18
+    %1 = ADD64ri8 %0, 4, implicit-def dead %eflags, debug-location !20
+    DBG_VALUE debug-use %1, debug-use _, !16, !17, debug-location !18
+    %3 = MOV32rm %0, 1, _, 0, _, debug-location !21 :: (load 4 from %ir.p.addr.0, !tbaa !22)
+    %4 = MOV64rm %rip, 1, _, target-flags(x86-gotpcrel) @x, _, debug-location !26 :: (load 8 from got)
+    MOV32mr killed %4, 1, _, 0, _, killed %3, debug-location !26 :: (store 4 into @x, !tbaa !22)
+    JMP_1 %bb.1.while.body, debug-location !27
+
+...