[EarlyCSE] Salvage debug info during DCE

[djtodoro]

Summary

EarlyCSE didn't try to salvage debug info during erasing of instructions. This fixes that.

[vsk]

I think the test case could probably be reduced a bit (is 'ctpop' necessary?), but apart from that, this looks good. @aprantl wdyt?

[davide]

test/Transforms/EarlyCSE/debuginfo-dce.ll

2–8

I'm under the impression this test case can be simplified. Can you give it a try?

[aprantl]

LGTM otherwise.

[djtodoro]

@vsk I have updated it. 'ctpop' is not necessary, there can be other intrinsic (e.g. 'bswap'). Thanks for the comment!
@aprantl Thanks!

test/Transforms/EarlyCSE/debuginfo-dce.ll

2–8

Yes, I have updated it. Thank you for the comment!

[davide]

LGTM modulo minor.

test/Transforms/EarlyCSE/debuginfo-dce.ll

3–4

unneeded.

[davide]

@djtodoro can you commit this or you need somebody to do it on your behalf?

[djtodoro]

@davide one of my colleagues will commit it

lib/Transforms/Scalar/EarlyCSE.cpp

bool EarlyCSE::processNode(DomTreeNode *Node) {
   // See if any instructions in the block can be eliminated.  If so, do it.  If
   // not, add them to AvailableValues.
   for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E;) {
     Instruction *Inst = &*I++;
 
     // Dead instructions should just be removed.
     if (isInstructionTriviallyDead(Inst, &TLI)) {
       DEBUG(dbgs() << "EarlyCSE DCE: " << *Inst << '\n');
+      salvageDebugInfo(*Inst);
       removeMSSA(Inst);
       Inst->eraseFromParent();
       Changed = true;
       ++NumSimplify;
       continue;
     }
 
     // Skip assume intrinsics, they don't really have side effects (although

test/Transforms/EarlyCSE/debuginfo-dce.ll

+; RUN: opt -early-cse -S %s -o - | FileCheck %s
+target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
+
+; Function Attrs: nounwind uwtable
+define i32 @foo() !dbg !6 {
+entry:
+  %0 = call i64 @llvm.ctpop.i64(i64 0), !dbg !14
+  %1 = inttoptr i64 %0 to i32*, !dbg !14
+  call void @llvm.dbg.value(metadata i32* %1, i64 0, metadata !11, metadata !13), !dbg !14
+; CHECK: call void @llvm.dbg.value(metadata i64 0, metadata !11, metadata !DIExpression()), !dbg !13
+  %call = call i32* (...) @baa(), !dbg !15
+  %2 = ptrtoint i32* %call to i64, !dbg !16
+  %3 = inttoptr i64 %2 to i32*, !dbg !16
+  call void @llvm.dbg.value(metadata i32* %3, i64 0, metadata !11, metadata !13), !dbg !14
+  %tobool = icmp ne i32* %3, null, !dbg !17
+  br i1 %tobool, label %if.end, label %if.then, !dbg !19
+
+if.then:                                          ; preds = %entry
+  br label %cleanup, !dbg !20
+
+if.end:                                           ; preds = %entry
+  %4 = ptrtoint i32* %3 to i32, !dbg !21
+  br label %cleanup, !dbg !22
+
+cleanup:                                          ; preds = %if.end, %if.then
+  %retval.0 = phi i32 [ %4, %if.end ], [ 0, %if.then ]
+  ret i32 %retval.0, !dbg !22
+}
+
+declare i32* @baa(...)
+
+; Function Attrs: nounwind readnone
+declare i64 @llvm.ctpop.i64(i64)
+
+; Function Attrs: nounwind readnone
+declare void @llvm.dbg.value(metadata, i64, metadata, metadata)
+
+!llvm.dbg.cu = !{!0}
+!llvm.module.flags = !{!3, !4}
+!llvm.ident = !{!5}
+
+!0 = distinct !DICompileUnit(language: DW_LANG_C99, file: !1, producer: "clang version 6.0.0", isOptimized: true, runtimeVersion: 0, emissionKind: FullDebug, enums: !2)
+!1 = !DIFile(filename: "test.c", directory: "/dir")
+!2 = !{}
+!3 = !{i32 2, !"Dwarf Version", i32 4}
+!4 = !{i32 2, !"Debug Info Version", i32 3}
+!5 = !{!"clang version 6.0.0"}
+!6 = distinct !DISubprogram(name: "foo", scope: !1, file: !1, line: 3, type: !7, isLocal: false, isDefinition: true, scopeLine: 3, isOptimized: true, unit: !0, variables: !10)
+!7 = !DISubroutineType(types: !8)
+!8 = !{!9}
+!9 = !DIBasicType(name: "int", size: 32, encoding: DW_ATE_signed)
+!10 = !{!11}
+!11 = !DILocalVariable(name: "ptr", scope: !6, file: !1, line: 4, type: !12)
+!12 = !DIDerivedType(tag: DW_TAG_pointer_type, baseType: !9, size: 64)
+!13 = !DIExpression()
+!14 = !DILocation(line: 4, column: 8, scope: !6)
+!15 = !DILocation(line: 5, column: 9, scope: !6)
+!16 = !DILocation(line: 5, column: 7, scope: !6)
+!17 = !DILocation(line: 7, column: 7, scope: !18)
+!18 = distinct !DILexicalBlock(scope: !6, file: !1, line: 7, column: 6)
+!19 = !DILocation(line: 7, column: 6, scope: !6)
+!20 = !DILocation(line: 8, column: 5, scope: !18)
+!21 = !DILocation(line: 10, column: 10, scope: !6)
+!22 = !DILocation(line: 11, column: 1, scope: !6)