[PATCH] D127134: [llvm] Add DW_CC_nocall to function debug metadata when either return values or arguments are removed

[Venkata Ramanaiah Nalamothu via Phabricator via llvm-commits]

RamNalamothu updated this revision to Diff 434722.
RamNalamothu retitled this revision from "[llvm][DeadArgumentElimination] Add DW_CC_nocall to function metadata when all return values are removed" to "[llvm] Add DW_CC_nocall to function debug metadata when either return values or arguments are removed".
RamNalamothu edited the summary of this revision.
RamNalamothu added a comment.

Address review feedback.


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D127134/new/

https://reviews.llvm.org/D127134

Files:
  llvm/include/llvm/IR/DebugInfoMetadata.h
  llvm/lib/Transforms/IPO/DeadArgumentElimination.cpp
  llvm/test/Transforms/DeadArgElim/2010-04-30-DbgInfo.ll


Index: llvm/test/Transforms/DeadArgElim/2010-04-30-DbgInfo.ll
===================================================================
--- llvm/test/Transforms/DeadArgElim/2010-04-30-DbgInfo.ll
+++ llvm/test/Transforms/DeadArgElim/2010-04-30-DbgInfo.ll
@@ -1,9 +1,12 @@
 ; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --function-signature
 ; RUN: opt -S -passes=deadargelim < %s | FileCheck %s
 
+; Apart from checking if debug metadata is correctly propagated, this also tests whether DW_CC_nocall
+; calling convention is added when either return values or arguments are removed.
+
 @.str = private constant [1 x i8] zeroinitializer, align 1 ; <[1 x i8]*> [#uses=1]
 
-define i8* @vfs_addname(i8* %name, i32 %len, i32 %hash, i32 %flags) nounwind ssp {
+define i8* @vfs_addname(i8* %name, i32 %len, i32 %hash, i32 %flags) nounwind ssp !dbg !1 {
 ;
 entry:
   call void @llvm.dbg.value(metadata i8* %name, metadata !0, metadata !DIExpression()), !dbg !DILocation(scope: !1)
@@ -17,7 +20,7 @@
 
 declare void @llvm.dbg.declare(metadata, metadata, metadata) nounwind readnone
 
-define internal fastcc i8* @add_name_internal(i8* %name, i32 %len, i32 %hash, i8 zeroext %extra, i32 %flags) noinline nounwind ssp {
+define internal fastcc i8* @add_name_internal(i8* %name, i32 %len, i32 %hash, i8 zeroext %extra, i32 %flags) noinline nounwind ssp !dbg !16 {
 ;
 entry:
   call void @llvm.dbg.value(metadata i8* %name, metadata !15, metadata !DIExpression()), !dbg !DILocation(scope: !16)
@@ -64,7 +67,10 @@
 !13 = !DILocation(line: 13, scope: !14)
 !14 = distinct !DILexicalBlock(line: 12, column: 0, file: !28, scope: !1)
 !15 = !DILocalVariable(name: "name", line: 17, arg: 1, scope: !16, file: !2, type: !6)
+; CHECK: !DISubprogram(name: "add_name_internal"
+; CHECK-SAME: type: ![[MD:[0-9]+]]
 !16 = distinct !DISubprogram(name: "add_name_internal", linkageName: "add_name_internal", line: 22, isLocal: true, isDefinition: true, virtualIndex: 6, isOptimized: false, unit: !3, file: !28, scope: !2, type: !17)
+; CHECK: ![[MD]] = !DISubroutineType(cc: DW_CC_nocall, types: !{{[0-9]+}})
 !17 = !DISubroutineType(types: !18)
 !18 = !{!6, !6, !9, !9, !19, !9}
 !19 = !DIBasicType(tag: DW_TAG_base_type, name: "unsigned char", size: 8, align: 8, encoding: DW_ATE_unsigned_char)
Index: llvm/lib/Transforms/IPO/DeadArgumentElimination.cpp
===================================================================
--- llvm/lib/Transforms/IPO/DeadArgumentElimination.cpp
+++ llvm/lib/Transforms/IPO/DeadArgumentElimination.cpp
@@ -23,6 +23,7 @@
 #include "llvm/IR/Attributes.h"
 #include "llvm/IR/BasicBlock.h"
 #include "llvm/IR/Constants.h"
+#include "llvm/IR/DIBuilder.h"
 #include "llvm/IR/DerivedTypes.h"
 #include "llvm/IR/Function.h"
 #include "llvm/IR/IRBuilder.h"
@@ -1083,6 +1084,14 @@
   for (auto MD : MDs)
     NF->addMetadata(MD.first, *MD.second);
 
+  // If either the return value(s) or argument(s) are removed, then probably the
+  // function does not follow standard calling conventions anymore. Hence add
+  // DW_CC_nocall to DISubroutineType to inform debugger that it may not safe to
+  // call this function or try to interpret the return value.
+  if (NFTy != FTy && NF->getSubprogram())
+    // Change the CallingConvention to DW_CC_nocall
+    NF->getSubprogram()->getType()->setCC(llvm::dwarf::DW_CC_nocall);
+
   // Now that the old function is dead, delete it.
   F->eraseFromParent();
 
Index: llvm/include/llvm/IR/DebugInfoMetadata.h
===================================================================
--- llvm/include/llvm/IR/DebugInfoMetadata.h
+++ llvm/include/llvm/IR/DebugInfoMetadata.h
@@ -1300,6 +1300,7 @@
   TempDISubroutineType clone() const { return cloneImpl(); }
 
   uint8_t getCC() const { return CC; }
+  void setCC(uint8_t NewCC) { CC = NewCC; }
 
   DITypeRefArray getTypeArray() const {
     return cast_or_null<MDTuple>(getRawTypeArray());


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