fix crash in machine trace metrics due to processing dbg_value instructions (PR24199)

[spatel]

Summary

The test in PR24199 ( https://llvm.org/bugs/show_bug.cgi?id=24199 ) crashes because machine trace metrics was not ignoring dbg_value instructions when calculating data dependencies.

The machine-combiner pass asks machine trace metrics to calculate an instruction trace, does some reassociations, and calls MachineInstr::eraseFromParentAndMarkDBGValuesForRemoval() along with MachineTraceMetrics::invalidate(). The dbg_value instructions have their operands invalidated, but the instructions are not expected to be deleted.

On a subsequent loop iteration of the machine-combiner pass, machine trace metrics would be called again and die while accessing the invalid debug instructions.

[Gerolf]

Thanks for fixing this. LGTM.
Is there a similar problem in getPHIDeps?

[spatel]

In D11423#210888, @Gerolf wrote:

Thanks for fixing this. LGTM.

Thanks for the review!

Is there a similar problem in getPHIDeps?

I thought that one was ok because we assert that the instruction is actually a PHI, so we know it's not a DBG_VALUE.

llvm/trunk/lib/CodeGen/MachineTraceMetrics.cpp

 };
 }
 
 // Get the input data dependencies that must be ready before UseMI can issue.
 // Return true if UseMI has any physreg operands.
 static bool getDataDeps(const MachineInstr *UseMI,
                         SmallVectorImpl<DataDep> &Deps,
                         const MachineRegisterInfo *MRI) {
+  // Debug values should not be included in any calculations.
+  if (UseMI->isDebugValue())
+    return false;
+  
   bool HasPhysRegs = false;
   for (MachineInstr::const_mop_iterator I = UseMI->operands_begin(),
        E = UseMI->operands_end(); I != E; ++I) {
     const MachineOperand &MO = *I;
     if (!MO.isReg())
       continue;
     unsigned Reg = MO.getReg();
     if (!Reg)

llvm/trunk/test/CodeGen/X86/machine-trace-metrics-crash.ll

+; RUN: llc -mtriple=x86_64-unknown-unknown -mcpu=x86-64 -mattr=sse -enable-unsafe-fp-math < %s | FileCheck %s
+
+; The debug info in this test case was causing a crash because machine trace metrics
+; did not correctly ignore debug instructions. The check lines ensure that the
+; machine-combiner pass has run, reassociated the add operands, and therefore
+; used machine trace metrics.
+
+define void @PR24199() {
+; CHECK-LABEL:  PR24199:
+; CHECK:  addss %xmm1, %xmm0
+; CHECK:  addss %xmm2, %xmm0
+
+entry:
+  %i = alloca %struct.A, align 8
+  %tobool = icmp ne i32 undef, 0
+  br i1 undef, label %if.end, label %if.then
+
+if.then:
+  br label %if.end
+
+if.end:
+  %h = phi float [ 0.0, %if.then ], [ 4.0, %entry ]
+  call void @foo(%struct.A* nonnull undef)
+  tail call void @llvm.dbg.value(metadata %struct.A* undef, i64 0, metadata !5, metadata !4), !dbg !6
+  tail call void @llvm.dbg.value(metadata float %h, i64 0, metadata !5, metadata !4), !dbg !6
+  %n0 = load float, float* undef, align 4
+  %mul = fmul fast float %n0, %h
+  %add = fadd fast float %mul, 1.0
+  tail call void @llvm.dbg.value(metadata %struct.A* undef, i64 0, metadata !5, metadata !4), !dbg !6
+  tail call void @llvm.dbg.value(metadata float %add, i64 0, metadata !5, metadata !4), !dbg !6
+  %add.i = fadd fast float %add, %n0
+  store float %add.i, float* undef, align 4
+  %n1 = bitcast %struct.A* %i to i8*
+  call void @llvm.lifetime.start(i64 16, i8* %n1)
+  %n2 = load <2 x float>, <2 x float>* undef, align 8
+  %conv = uitofp i1 %tobool to float
+  %bitcast = extractelement <2 x float> %n2, i32 0
+  %factor = fmul fast float %bitcast, 2.0
+  %add3 = fadd fast float %factor, %conv
+  call void @bar(float %add3)
+  ret void
+}
+
+%struct.A = type { float, float }
+
+declare void @bar(float)
+declare void @foo(%struct.A*)
+declare void @llvm.lifetime.start(i64, i8* nocapture)
+declare void @llvm.dbg.value(metadata, i64, metadata, metadata)
+
+!llvm.dbg.cu = !{!0}
+!llvm.module.flags = !{!2}
+
+!0 = distinct !DICompileUnit(language: DW_LANG_C_plus_plus, file: !1, isOptimized: true, runtimeVersion: 0, emissionKind: 1)
+!1 = !DIFile(filename: "24199.cpp", directory: "/bin")
+!2 = !{i32 2, !"Debug Info Version", i32 3}
+!3 = !DISubprogram(linkageName: "foo", file: !1, line: 18, isLocal: false, isDefinition: true, scopeLine: 18, function: void (%struct.A*)* @foo)
+!4 = !DIExpression()
+!5 = !DILocalVariable(tag: DW_TAG_arg_variable, name: "this", arg: 1, scope: !3, flags: DIFlagArtificial | DIFlagObjectPointer)
+!6 = !DILocation(line: 0, scope: !3)
+
+