[mips] fix -mfix4300

[Random06457]

Summary

When compiling with dwarf info, the mfix4300 flag introduced in https://reviews.llvm.org/D116238 can miss some occurrences of the vr4300 mulmul bug if a debug instruction happens to be between two muls.
This revision skips debug instructions in order to fix the mulmul bug detection.

Fixes https://github.com/llvm/llvm-project/issues/53094

[Random06457]

By the way, last time I made a contribution, the address that was used for the commit was the address I entered on phabricator to receive notifications.
Since I'm new to LLVM/phabricator I'm not sure where to ask if there's a way to make it so my github address ([e-mail]) is used instead for commits.
I can't get this address verified on phabricator since it's a noreply address.

[atanasyan]

LGTM with a small fix. I will commit the changes shortly.

llvm/lib/Target/Mips/MipsMulMulBugPass.cpp

120

You can use the next_nodbg function to write this line as NextMII = next_nodbg(MII, E);.

llvm/lib/Target/Mips/MipsMulMulBugPass.cpp

default:
     return false;
   }
 }
 
 bool MipsMulMulBugFix::fixMulMulBB(MachineBasicBlock &MBB,
                                    const MipsInstrInfo &MipsII) {
   bool Modified = false;
 
+  MachineBasicBlock::instr_iterator NextMII;
+
   // Iterate through the instructions in the basic block
   for (MachineBasicBlock::instr_iterator MII = MBB.instr_begin(),
                                          E = MBB.instr_end();
-       MII != E; ++MII) {
+       MII != E; MII = NextMII) {
 
-    MachineBasicBlock::instr_iterator NextMII = std::next(MII);
+    NextMII = next_nodbg(MII, E);
 
     // Trigger when the current instruction is a mul and the next instruction
     // is either a mul or a branch in case the branch target start with a mul
     if (NextMII != E && isFirstMul(*MII) && isSecondMulOrBranch(*NextMII)) {
-      LLVM_DEBUG(dbgs() << "Found mulmul!");
+      LLVM_DEBUG(dbgs() << "Found mulmul!\n");
 
       const MCInstrDesc &NewMCID = MipsII.get(Mips::NOP);
       BuildMI(MBB, NextMII, DebugLoc(), NewMCID);
       Modified = true;
     }
   }
 
   return Modified;
 }
 
 FunctionPass *llvm::createMipsMulMulBugPass() { return new MipsMulMulBugFix(); }

llvm/test/CodeGen/Mips/vr4300-mulmul.ll

 ; RUN: llc -march=mips -mfix4300 -verify-machineinstrs < %s | FileCheck %s
 
 ; Function Attrs: mustprogress nofree norecurse nosync nounwind readnone willreturn
-define dso_local float @fun_s(float %x) local_unnamed_addr #0 {
+define dso_local float @fun_s(float %x) local_unnamed_addr !dbg !7  {
 entry:
 ; CHECK-LABEL: fun_s
 ; CHECK: mul.s
+; CHECK-NEXT: #DEBUG_VALUE: i <- 1
 ; CHECK-NEXT: nop
-; CHECK: mul.s
   %mul = fmul float %x, %x
+  call void @llvm.dbg.value(metadata i32 1, metadata !13, metadata !DIExpression()), !dbg !17
   %mul1 = fmul float %mul, %x
   ret float %mul1
 }
 
 define dso_local double @fun_d(double %x) local_unnamed_addr #0 {
 entry:
 ; CHECK-LABEL: fun_d
 ; CHECK: mul.d
 ; CHECK-NEXT: nop
 ; CHECK: mul.d
   %mul = fmul double %x, %x
   %mul1 = fmul double %mul, %x
   ret double %mul1
 }
+
+
+; Function Attrs: nofree nosync nounwind readnone speculatable willreturn
+declare void @llvm.dbg.value(metadata, metadata, metadata)
+
+!llvm.dbg.cu = !{!0}
+!llvm.module.flags = !{!2, !3}
+
+!0 = distinct !DICompileUnit(language: DW_LANG_C_plus_plus_14, file: !1, producer: "", isOptimized: true, runtimeVersion: 0, emissionKind: FullDebug, splitDebugInlining: false, nameTableKind: None)
+!1 = !DIFile(filename: "vr4300-mulmul.ll", directory: "/")
+!2 = !{i32 7, !"Dwarf Version", i32 4}
+!3 = !{i32 2, !"Debug Info Version", i32 3}
+!7 = distinct !DISubprogram(name: "fun_s", linkageName: "fun_s", scope: !1, file: !1, line: 1, type: !8, scopeLine: 2, flags: DIFlagPrototyped | DIFlagAllCallsDescribed, spFlags: DISPFlagDefinition | DISPFlagOptimized, unit: !0)
+!8 = !DISubroutineType(types: !9)
+!9 = !{!10, !10}
+!10 = !DIBasicType(name: "float", size: 32, encoding: DW_ATE_float)
+!13 = !DILocalVariable(name: "i", scope: !14, file: !1, line: 3, type: !15)
+!14 = distinct !DILexicalBlock(scope: !7, file: !1, line: 3, column: 5)
+!15 = !DIBasicType(name: "int", size: 32, encoding: DW_ATE_signed)
+!17 = !DILocation(line: 0, scope: !14)