Fix debug info for SelectionDAG legalization of DAG nodes with two results.

[aprantl]

Summary

This patch fixes the debug info handling for SelectionDAG legalization of DAG nodes with two results. When an replaced SDNode has more than one result, transferDbgValues was always copying the SDDbgValue from the first result and attaching them to all members. In reality SelectionDAG::ReplaceAllUsesWith() is given an array of SDNodes (though the type signature doesn't make this obvious (cf. the call site code in ReplaceNode()).

[vsk]

LGTM, possibly with an added assert. The test looks great!

lib/CodeGen/SelectionDAG/SelectionDAG.cpp

7793

Should we assert the first requirement here, i.e From->getNumValues() == To->getNumValues()?

[aprantl]

lib/CodeGen/SelectionDAG/SelectionDAG.cpp

7793

That's not possible, unfortunately, an SDNode can have multiple results each of which is an SDValue. We could change the function to take SmallVectorImpl instead though.

7793

I'll do that in a follow-up commit.

lib/CodeGen/SelectionDAG/SelectionDAG.cpp

#endif
   if (From == getRoot().getNode())
     setRoot(SDValue(To, getRoot().getResNo()));
 }
 
 /// ReplaceAllUsesWith - Modify anything using 'From' to use 'To' instead.
 /// This can cause recursive merging of nodes in the DAG.
 ///
 /// This version can replace From with any result values.  To must match the
 /// number and types of values returned by From.
 void SelectionDAG::ReplaceAllUsesWith(SDNode *From, const SDValue *To) {
   if (From->getNumValues() == 1)  // Handle the simple case efficiently.
     return ReplaceAllUsesWith(SDValue(From, 0), To[0]);
 
   // Preserve Debug Info.
   for (unsigned i = 0, e = From->getNumValues(); i != e; ++i)
-    transferDbgValues(SDValue(From, i), *To);
+    transferDbgValues(SDValue(From, i), To[i]);
 
   // Iterate over just the existing users of From. See the comments in
   // the ReplaceAllUsesWith above.
   SDNode::use_iterator UI = From->use_begin(), UE = From->use_end();
   RAUWUpdateListener Listener(*this, UI, UE);
   while (UI != UE) {
     SDNode *User = *UI;
 

test/DebugInfo/X86/sdag-legalize-multires.ll

+; RUN: llc -O0 %s -stop-after=livedebugvars -o - | FileCheck %s
+; This is a hand-crafted example modified after some Swift compiler output.
+; Test that SelectionDAG legalization of DAG nodes with two results
+; transfers debug info correctly.
+
+source_filename = "/tmp/sincos.ll"
+target datalayout = "e-m:o-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-apple-macosx10.13.0"
+
+declare float @llvm.cos.f32(float)
+declare float @llvm.sin.f32(float)
+declare void @llvm.dbg.value(metadata, metadata, metadata)
+declare swiftcc void @g(float, float)
+
+; CHECK: ![[RCOS:.*]] = !DILocalVariable(name: "rcos"
+; CHECK: ![[RSIN:.*]] = !DILocalVariable(name: "rsin"
+
+define hidden swiftcc void @f() #0 !dbg !8 {
+entry:
+  ; CHECK: CALL64pcrel32 &__sincosf_stret
+  %0 = call float @llvm.cos.f32(float 1.500000e+00), !dbg !13
+  ; CHECK: $xmm1 = MOVAPSrr $xmm0
+  call void @llvm.dbg.value(metadata float %0, metadata !15, metadata !DIExpression()), !dbg !13
+  ; CHECK: DBG_VALUE debug-use {{.*}}$xmm1, {{.*}}, ![[RSIN]], !DIExpression(),
+  %1 = call float @llvm.sin.f32(float 1.500000e+00), !dbg !13
+  call void @llvm.dbg.value(metadata float %1, metadata !11, metadata !DIExpression()), !dbg !13
+  ; CHECK: DBG_VALUE debug-use {{.*}}$xmm0, {{.*}}, ![[RCOS]], !DIExpression(),
+  call void @g(float %0, float %1), !dbg !13
+  ret void, !dbg !13
+}
+
+attributes #0 = { noinline nounwind optnone ssp uwtable "target-features"="+sse,+sse2,+sse3,+sse4.1,+ssse3,+x87" }
+
+!llvm.dbg.cu = !{!0}
+!llvm.module.flags = !{!3, !4}
+
+!0 = distinct !DICompileUnit(language: DW_LANG_C99, file: !1, producer: "clang version 8.0.0 (trunk 340541) (llvm/trunk 340540)", isOptimized: false, runtimeVersion: 0, emissionKind: FullDebug, enums: !2, nameTableKind: None)
+!1 = !DIFile(filename: "sincos.ll", directory: "/")
+!2 = !{}
+!3 = !{i32 2, !"Dwarf Version", i32 4}
+!4 = !{i32 2, !"Debug Info Version", i32 3}
+!8 = distinct !DISubprogram(name: "f", scope: !1, file: !1, line: 2, type: !9, isLocal: false, isDefinition: true, scopeLine: 2, isOptimized: false, unit: !0, retainedNodes: !2)
+!9 = !DISubroutineType(types: !10)
+!10 = !{null}
+!11 = !DILocalVariable(name: "rsin", scope: !8, file: !1, line: 3, type: !12)
+!12 = !DIBasicType(name: "float", size: 32, encoding: DW_ATE_float)
+!13 = !DILocation(line: 3, scope: !8)
+!15 = !DILocalVariable(name: "rcos", scope: !8, file: !1, line: 4, type: !12)