Fix possible assertion when using PBQP with debug info

[danilaml]

Summary

Skip debug instructions before calling functions not expecting them.
In particular, LIS.getInstructionIndex(*mi) would fail if mi was a debg instr.

[danilaml]

Test generated from the following C code:

#include <stdint.h>

void test(int16_t* a, int16_t* b, int16_t* c, uint32_t n) {
    for (int32_t i = 0; i < n; i++) {
        *c++ = *a++ + *b++;
    }
}

llvm/lib/CodeGen/CalcSpillWeights.cpp

218

Don't think that counting uses in debug instrs was originally intended for this heuristic.

[aprantl]

Looks generally good, except for the test.

llvm/test/CodeGen/Generic/csw-debug-assert.ll

3

Please add a comment explaining what is being tested here

Please add something that explicitly CHECKs the results? Otherwise this test will succeed even if someone symlinks /bin/true to llc :-)

55

Please delete all nonnecessary attributes, it makes the tests hard to maintain

[danilaml]

llvm/test/CodeGen/Generic/csw-debug-assert.ll

3

Done.

From what it seems, the majority of the lit tests are vulnerable to /bin/true trick ;P

55

Done. It's a bit hard to know what's necessary or not when ll is generated from simple C code and not hand-crafted (and you can't just remove all metadata).

[aprantl]

llvm/test/CodeGen/Generic/csw-debug-assert.ll

12

How about checking at least some of the contents of the DBG_VALUE?

110

You can probably significantly shorten the test by manually assigning all instructions the same !dbg location.

[aprantl]

LGTM with all outstanding comments addressed.

[danilaml]

llvm/test/CodeGen/Generic/csw-debug-assert.ll

110

I've simplified the test. Do you think manual dbg hacking is still necessary?

[aprantl]

llvm/test/CodeGen/Generic/csw-debug-assert.ll

76

Do you need the TBAAA info?

110

Getting the tests as minimal as possible helps in the long term with maintenance. All tests need to updated occasionally for various IR changes and then it really helps to know what is relevant to the test and what isn't. So, I would do it, since it's not a lot of work and helps focus on what's important.

[danilaml]

llvm/test/CodeGen/Generic/csw-debug-assert.ll

110

My concern here that by manually editing .ll metadata I might accidentally break some underlying assumption which might lead to problems later down the line. Anyway, I'll try to clean DILocations up.

llvm/lib/CodeGen/CalcSpillWeights.cpp

bool operator<(const CopyHint &rhs) const {
         return (IsPhys && !rhs.IsPhys);
       if (Weight != rhs.Weight)
         return (Weight > rhs.Weight);
       return Reg < rhs.Reg; // Tie-breaker.
     }
   };
   std::set<CopyHint> CopyHints;
 
-  for (MachineRegisterInfo::reg_instr_iterator
-       I = mri.reg_instr_begin(li.reg), E = mri.reg_instr_end();
-       I != E; ) {
+  for (MachineRegisterInfo::reg_instr_nodbg_iterator
+           I = mri.reg_instr_nodbg_begin(li.reg),
+           E = mri.reg_instr_nodbg_end();
+       I != E;) {
     MachineInstr *mi = &*(I++);
 
     // For local split artifacts, we are interested only in instructions between
     // the expected start and end of the range.
     SlotIndex si = LIS.getInstructionIndex(*mi);
     if (localSplitArtifact && ((si < *start) || (si > *end)))
       continue;
 
     numInstr++;
-    if (mi->isIdentityCopy() || mi->isImplicitDef() || mi->isDebugInstr())
+    if (mi->isIdentityCopy() || mi->isImplicitDef())
       continue;
     if (!visited.insert(mi).second)
       continue;
 
     float weight = 1.0f;
     if (Spillable) {
       // Get loop info for mi.
       if (mi->getParent() != mbb) {

llvm/test/CodeGen/Generic/csw-debug-assert.ll

+; Check that compiler doesn't crash when calculateSpillWeightsAndHints is called with dbg instrs present
+; REQUIRES: asserts
+; RUN: llc -O1 -regalloc=pbqp < %s | FileCheck %s
+
+target datalayout = "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-unknown-linux-gnu"
+
+; CHECK-LABEL: test:
+define dso_local void @test(i32* %a) local_unnamed_addr #0 !dbg !7 {
+entry:
+  ; CHECK: DEBUG_VALUE: i <- 0
+  call void @llvm.dbg.value(metadata i32* %a, metadata !14, metadata !DIExpression()), !dbg !17
+  call void @llvm.dbg.value(metadata i32 0, metadata !15, metadata !DIExpression()), !dbg !18
+  br label %for.cond, !dbg !19
+
+for.cond:                                         ; preds = %for.body, %entry
+  %a.addr.0 = phi i32* [ %a, %entry ], [ %incdec.ptr, %for.body ]
+  %i.0 = phi i32 [ 0, %entry ], [ %inc, %for.body ], !dbg !18
+  call void @llvm.dbg.value(metadata i32 %i.0, metadata !15, metadata !DIExpression()), !dbg !18
+  call void @llvm.dbg.value(metadata i32* %a.addr.0, metadata !14, metadata !DIExpression()), !dbg !17
+  %cmp = icmp slt i32 %i.0, 32, !dbg !20
+  br i1 %cmp, label %for.body, label %for.cond.cleanup, !dbg !22
+
+for.cond.cleanup:                                 ; preds = %for.cond
+  ret void, !dbg !23
+
+for.body:                                         ; preds = %for.cond
+  %incdec.ptr = getelementptr inbounds i32, i32* %a.addr.0, i32 1, !dbg !24
+  call void @llvm.dbg.value(metadata i32* %incdec.ptr, metadata !14, metadata !DIExpression()), !dbg !17
+  store i32 42, i32* %a.addr.0, align 4, !dbg !26, !tbaa !27
+  %inc = add nsw i32 %i.0, 1, !dbg !31
+  call void @llvm.dbg.value(metadata i32 %inc, metadata !15, metadata !DIExpression()), !dbg !18
+  br label %for.cond, !dbg !32, !llvm.loop !33
+}
+
+; Function Attrs: nounwind readnone speculatable willreturn
+declare void @llvm.dbg.value(metadata, metadata, metadata) #1
+
+attributes #0 = { nounwind uwtable optnone noinline }
+attributes #1 = { nounwind readnone speculatable willreturn }
+
+!llvm.dbg.cu = !{!0}
+!llvm.module.flags = !{!3, !4, !5}
+!llvm.ident = !{!6}
+
+!0 = distinct !DICompileUnit(language: DW_LANG_C99, file: !1, producer: "clang version 11.0.0 (https://github.com/llvm/llvm-project.git afaeb817468d2fdc0a315a7ff136db245e59a8eb)", isOptimized: true, runtimeVersion: 0, emissionKind: FullDebug, enums: !2, splitDebugInlining: false, nameTableKind: None)
+!1 = !DIFile(filename: "csw-debug-assert.c", directory: "dir")
+!2 = !{}
+!3 = !{i32 7, !"Dwarf Version", i32 4}
+!4 = !{i32 2, !"Debug Info Version", i32 3}
+!5 = !{i32 1, !"wchar_size", i32 4}
+!6 = !{!"clang version 11.0.0 (https://github.com/llvm/llvm-project.git afaeb817468d2fdc0a315a7ff136db245e59a8eb)"}
+!7 = distinct !DISubprogram(name: "test", scope: !8, file: !8, line: 5, type: !9, scopeLine: 5, flags: DIFlagPrototyped | DIFlagAllCallsDescribed, spFlags: DISPFlagDefinition | DISPFlagOptimized, unit: !0, retainedNodes: !13)
+!8 = !DIFile(filename: "csw-debug-assert.c", directory: "dir")
+!9 = !DISubroutineType(types: !10)
+!10 = !{null, !11}
+!11 = !DIDerivedType(tag: DW_TAG_pointer_type, baseType: !12, size: 64)
+!12 = !DIBasicType(name: "int", size: 32, encoding: DW_ATE_signed)
+!13 = !{!14, !15}
+!14 = !DILocalVariable(name: "a", arg: 1, scope: !7, file: !8, line: 5, type: !11)
+!15 = !DILocalVariable(name: "i", scope: !16, file: !8, line: 6, type: !12)
+!16 = distinct !DILexicalBlock(scope: !7, file: !8, line: 6, column: 5)
+!17 = !DILocation(line: 0, scope: !7)
+!18 = !DILocation(line: 0, scope: !16)
+!19 = !DILocation(line: 6, column: 10, scope: !16)
+!20 = !DILocation(line: 6, column: 23, scope: !21)
+!21 = distinct !DILexicalBlock(scope: !16, file: !8, line: 6, column: 5)
+!22 = !DILocation(line: 6, column: 5, scope: !16)
+!23 = !DILocation(line: 9, column: 1, scope: !7)
+!24 = !DILocation(line: 7, column: 11, scope: !25)
+!25 = distinct !DILexicalBlock(scope: !21, file: !8, line: 6, column: 34)
+!26 = !DILocation(line: 7, column: 14, scope: !25)
+!27 = !{!28, !28, i64 0}
+!28 = !{!"int", !29, i64 0}
+!29 = !{!"omnipotent char", !30, i64 0}
+!30 = !{!"Simple C/C++ TBAA"}
+!31 = !DILocation(line: 6, column: 30, scope: !21)
+!32 = !DILocation(line: 6, column: 5, scope: !21)
+!33 = distinct !{!33, !22, !34}
+!34 = !DILocation(line: 8, column: 5, scope: !16)