[llvm] [DebugInfo][RemoveDIs] Add a DPValue implementation for instcombine sinking (PR #77930)

[Stephen Tozer via llvm-commits]

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@@ -0,0 +1,74 @@
+; RUN: opt %s -o - -S --passes=instcombine | FileCheck %s
+; RUN: opt %s -o - -S --passes=instcombine --try-experimental-debuginfo-iterators | FileCheck %s
+;
+; CHECK-LABEL: for.body:
+; CHECK-NEXT:  %sub.ptr.rhs.cast.i.i = ptrtoint ptr %call2.i.i to i64,
+; CHECK-NEXT:  tail call void @llvm.dbg.value(metadata i64 %sub.ptr.rhs.cast.i.i, metadata !{{[0-9]*}}, metadata !DIExpression(DW_OP_LLVM_convert, 64, DW_ATE_unsigned, DW_OP_LLVM_convert, 32, DW_ATE_unsigned, DW_OP_constu, 1, DW_OP_minus, DW_OP_stack_value)
+;
+;; The code below is representative of a common situation: where we've had a
+;; loop be completely optimised out, leaving dbg.values representing the
+;; assignments for it, including a rotated assignment to the loop counter.
+;; Below, it's the two dbg.values in the entry block, assigning first the
+;; value of %conv.i, then the value of %conv.i minus one.
+;;
+;; When instcombine sinks %conv.i, it's critical that if it sinks a dbg.value
+;; with it, it sinks the most recent assignment. Otherwise it will re-order the
+;; assignments below, and a fall counter assignment will continue on from the
+;; end of the optimised-out loop.
+;;
+;; The check lines test that when the trunc sinks (along with the ptrtoint),
+;; we get the dbg.value with a DW_OP_minus in it.
+
+; ModuleID = 'tmp.ll'
+source_filename = "tmp.ll"
+target datalayout = "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-i128:128-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-unknown-linux-gnu"
+
+declare void @llvm.dbg.value(metadata, metadata, metadata)
+declare void @llvm.dbg.declare(metadata, metadata, metadata)
+
+define void @_ZN4llvm16MCObjectStreamer15EmitInstructionERKNS_6MCInstE(i1 %tobool.not) local_unnamed_addr {
+entry:
+  %call2.i.i = load volatile ptr, ptr null, align 8, !dbg !4
+  %sub.ptr.rhs.cast.i.i = ptrtoint ptr %call2.i.i to i64, !dbg !4
+  %conv.i = trunc i64 %sub.ptr.rhs.cast.i.i to i32, !dbg !4
+  tail call void @llvm.dbg.value(metadata i32 %conv.i, metadata !16, metadata !DIExpression()), !dbg !18
+  tail call void @llvm.dbg.value(metadata i32 %conv.i, metadata !16, metadata !DIExpression(DW_OP_constu, 1, DW_OP_minus, DW_OP_stack_value)), !dbg !18
+  br i1 %tobool.not, label %common.ret, label %for.body
+
+common.ret:                                       ; preds = %for.body, %entry
+  ret void
+
+for.body:                                         ; preds = %entry
+  %call2 = call ptr @_ZNK4llvm6MCInst10getOperandEj(i32 %conv.i)
+  br label %common.ret
+}
+
+declare i32 @_ZNK4llvm6MCInst14getNumOperandsEv()
+
+declare ptr @_ZNK4llvm6MCInst10getOperandEj(i32) local_unnamed_addr
+
+declare i64 @_ZNK4llvm25SmallVectorTemplateCommonINS_9MCOperandEvE4sizeEv()
+
+!llvm.dbg.cu = !{!0}
+!llvm.module.flags = !{!3}
+
+!0 = distinct !DICompileUnit(language: DW_LANG_C_plus_plus_14, file: !1, isOptimized: true, runtimeVersion: 0, emissionKind: FullDebug, enums: !2, retainedTypes: !2, globals: !2, imports: !2, splitDebugInlining: false, nameTableKind: None)
+!1 = !DIFile(filename: "/fast/fs/llvm34/lib/MC/MCObjectStreamer.cpp", directory: "/fast/fs/build34llvmstage", checksumkind: CSK_MD5, checksum: "43f3adff5ece50116e446307bd92824d")
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SLTozer wrote:

Nit, we can remove the useless metadata e.g. checksums.

https://github.com/llvm/llvm-project/pull/77930