[CGP] Reset the debug location when promoting trunc(s)

[davide]

Summary

Spun off from https://reviews.llvm.org/D81437

[davide]

This is the same issue of D81437, when hoisting/promoting the trunc we don't want to assign it a location that could cause a jump in the line table.

[davide]

Context + simplified testcase.

[vsk]

Thanks, lgtm. I had a look at the other TypePromotionActions in CodeGenPrepare: I think it'd be better to default to these /not/ carrying over debug locations, even though in some cases it would be appropriate to do so (e.g. if the instruction reordering is block-local), just because there's so much cross-BB movement.

[davide]

Yes, I agree. I'm going to craft test cases for these too.

[davide]

Committed in:

commit c2dccf9d5e34278cb2ed0a018405848850508b99 (HEAD -> master, origin/master, origin/HEAD)
Author: Davide Italiano <[e-mail]>
Date:   Mon Jun 15 14:25:30 2020 -0700

    [CodeGenPrepare] Reset the debug location when promoting trunc(s)
    
    The promotion machinery in CGP moves instructions retaining
    debug locations. When the transformation is local, this is mostly
    correct, but when instructions are moved cross-BBs, this is not
    always true and causes jumpiness in line tables. This is the first
    of a series of commits. sext(s) and zext(s) need to be treated
    similarly.
    
    Differential Revision:  https://reviews.llvm.org/D81879

llvm/lib/CodeGen/CodeGenPrepare.cpp

class TruncBuilder : public TypePromotionAction {
     Value *Val;
 
   public:
     /// Build a truncate instruction of \p Opnd producing a \p Ty
     /// result.
     /// trunc Opnd to Ty.
     TruncBuilder(Instruction *Opnd, Type *Ty) : TypePromotionAction(Opnd) {
       IRBuilder<> Builder(Opnd);
+      Builder.SetCurrentDebugLocation(DebugLoc());
       Val = Builder.CreateTrunc(Opnd, Ty, "promoted");
       LLVM_DEBUG(dbgs() << "Do: TruncBuilder: " << *Val << "\n");
     }
 
     /// Get the built value.
     Value *getBuiltValue() { return Val; }
 
     /// Remove the built instruction.

llvm/test/Transforms/CodeGenPrepare/X86/promoted-trunc-loc.ll

+; RUN: opt < %s -codegenprepare -S -mtriple=x86_64-unknown-unknown | FileCheck %s
+
+; Make sure the promoted trunc doesn't get a debug location associated.
+; CHECK: %promoted = trunc i32 %or to i16
+
+target datalayout = "e-m:o-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-apple-macosx10.13.0"
+
+@b = global i16 0, align 2
+
+declare void @bar(i64)
+
+define i32 @foo(i16 %kkk) !dbg !6 {
+entry:
+  %t4 = load i16, i16* @b, align 2, !dbg !8
+  %conv4 = zext i16 %t4 to i32, !dbg !9
+  %or = or i16 %kkk, %t4, !dbg !10
+  %c = sext i16 %or to i64, !dbg !11
+  call void @bar(i64 %c), !dbg !12
+  %t5 = and i16 %or, 5, !dbg !13
+  %z = zext i16 %t5 to i32, !dbg !14
+  ret i32 %z, !dbg !15
+}
+
+!llvm.dbg.cu = !{!0}
+!llvm.debugify = !{!3, !4}
+!llvm.module.flags = !{!5}
+
+!0 = distinct !DICompileUnit(language: DW_LANG_C, file: !1, producer: "debugify", isOptimized: true, runtimeVersion: 0, emissionKind: FullDebug, enums: !2)
+!1 = !DIFile(filename: "/Users/davide/work/llvm-project/patatino.ll", directory: "/")
+!2 = !{}
+!3 = !{i32 8}
+!4 = !{i32 0}
+!5 = !{i32 2, !"Debug Info Version", i32 3}
+!6 = distinct !DISubprogram(name: "foo", linkageName: "foo", scope: null, file: !1, line: 1, type: !7, scopeLine: 1, spFlags: DISPFlagDefinition | DISPFlagOptimized, unit: !0, retainedNodes: !2)
+!7 = !DISubroutineType(types: !2)
+!8 = !DILocation(line: 1, column: 1, scope: !6)
+!9 = !DILocation(line: 2, column: 1, scope: !6)
+!10 = !DILocation(line: 3, column: 1, scope: !6)
+!11 = !DILocation(line: 4, column: 1, scope: !6)
+!12 = !DILocation(line: 5, column: 1, scope: !6)
+!13 = !DILocation(line: 6, column: 1, scope: !6)
+!14 = !DILocation(line: 7, column: 1, scope: !6)
+!15 = !DILocation(line: 8, column: 1, scope: !6)