[PATCH] D61184: [Salvage] Change salvage debug info implementation to use new DW_OP_LLVM_convert where needed

[Stephen Tozer via Phabricator via llvm-commits]

StephenTozer created this revision.
StephenTozer added reviewers: markus, vsk, probinson, aprantl, dblaikie.
Herald added subscribers: llvm-commits, hiraditya.
Herald added a project: LLVM.

Fixes issue: https://bugs.llvm.org/show_bug.cgi?id=40645

Previously, LLVM had no functional way of performing casts inside of a DIExpression(), which made salvaging cast instructions other than Noop casts impossible. With the recent addition of DW_OP_LLVM_convert this salvaging is now possible, and so can be used to fix the attached bug as well as any cases where ZExt or SExt instruction results are lost in the debugging metadata. This patch introduces this fix by expanding the salvage debug info method to cover these cases using the new operator.


Repository:
  rL LLVM

https://reviews.llvm.org/D61184

Files:
  llvm/lib/Transforms/Utils/Local.cpp
  llvm/test/DebugInfo/salvage-cast-debug-info.ll
  llvm/test/Transforms/InstCombine/cast-mul-select.ll


Index: llvm/test/Transforms/InstCombine/cast-mul-select.ll
===================================================================
--- llvm/test/Transforms/InstCombine/cast-mul-select.ll
+++ llvm/test/Transforms/InstCombine/cast-mul-select.ll
@@ -13,6 +13,8 @@
 ; we preserve the debug information in the resulting
 ; instruction.
 ; DBGINFO-LABEL: @mul(
+; DBGINFO-NEXT:    call void @llvm.dbg.value(metadata i32 %x
+; DBGINFO-NEXT:    call void @llvm.dbg.value(metadata i32 %y
 ; DBGINFO-NEXT:    [[C:%.*]] = mul i32 {{.*}}
 ; DBGINFO-NEXT:    [[D:%.*]] = and i32 {{.*}}
 ; DBGINFO-NEXT:    call void @llvm.dbg.value(metadata i32 [[C]]
Index: llvm/test/DebugInfo/salvage-cast-debug-info.ll
===================================================================
--- /dev/null
+++ llvm/test/DebugInfo/salvage-cast-debug-info.ll
@@ -0,0 +1,25 @@
+; RUN: opt %s -debugify -early-cse -S | FileCheck %s
+define i32 @foo(i64 %nose, i32 %more) {
+; CHECK-LABEL: @foo(
+; CHECK: call void @llvm.dbg.value(metadata i64 %nose, metadata [[V1:![0-9]+]], metadata !DIExpression(DW_OP_LLVM_convert, 32
+; CHECK: call void @llvm.dbg.value(metadata i64 %nose.shift, metadata [[V2:![0-9]+]]
+; CHECK: call void @llvm.dbg.value(metadata i64 %nose.shift, metadata [[V3:![0-9]+]], metadata !DIExpression(DW_OP_LLVM_convert, 32
+
+entry:
+  %nose.trunc = trunc i64 %nose to i32
+  %nose.shift = lshr i64 %nose, 32
+  %nose.trunc.2 = trunc i64 %nose.shift to i32
+  %add = add nsw i32 %more, 1
+  ret i32 %add
+}
+
+!llvm.module.flags = !{!0, !1}
+!llvm.ident = !{!2}
+
+!0 = !{i32 1, !"wchar_size", i32 2}
+!1 = !{i32 7, !"PIC Level", i32 2}
+!2 = !{!"clang version 9.0.0 "}
+
+; CHECK: [[V1]] = !DILocalVariable(
+; CHECK: [[V2]] = !DILocalVariable(
+; CHECK: [[V3]] = !DILocalVariable(
Index: llvm/lib/Transforms/Utils/Local.cpp
===================================================================
--- llvm/lib/Transforms/Utils/Local.cpp
+++ llvm/lib/Transforms/Utils/Local.cpp
@@ -1669,6 +1669,22 @@
     // No-op casts and zexts are irrelevant for debug info.
     if (CI->isNoopCast(DL) || isa<ZExtInst>(&I))
       return SrcDIExpr;
+    Type *Type = CI->getType();
+    // There does not appear to be any op for vector casting.
+    if (Type->isVectorTy())
+      return nullptr;
+
+    if (isa<TruncInst>(&I) || isa<ZExtInst>(&I) || isa<SExtInst>(&I)) {
+      unsigned TypeBitSize = Type->getScalarSizeInBits();
+
+      // The result of the cast will be sign extended iff the instruction is a
+      // SExt; signedness is otherwise irrelevant on the expression stack.
+      unsigned Encoding =
+          isa<SExtInst>(&I) ? dwarf::DW_ATE_signed : dwarf::DW_ATE_unsigned;
+
+      return applyOps({dwarf::DW_OP_LLVM_convert, TypeBitSize, Encoding});
+    }
+
     return nullptr;
   } else if (auto *GEP = dyn_cast<GetElementPtrInst>(&I)) {
     unsigned BitWidth =


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