From 09d8ea5282505251a3da5cebb6ec7c7e0e685db2 Mon Sep 17 00:00:00 2001
From: Jeremy Morse <jeremy.morse.llvm@gmail.com>
Date: Mon, 4 Mar 2019 10:56:02 +0000
Subject: [PATCH] [X86] Avoid codegen changes when DBG_VALUE appears between
 lowered selects

X86TargetLowering::EmitLoweredSelect presently detects sequences of CMOV pseudo
instructions without accounting for debug intrinsics. This leads to different
codegen with and without option -g, if a DBG_VALUE instruction lands in the
middle of several lowered selects.

Work around this by skipping over debug instructions when looking for CMOV
sequences, and sinking those debug insts into the EmitLoweredSelect sunk block.
This might slightly shift where variables appear in the instruction sequence,
but won't re-order assignments.

Differential Revision: https://reviews.llvm.org/D58672

llvm-svn: 355307
---
 llvm/lib/Target/X86/X86ISelLowering.cpp     | 19 ++++++--
 llvm/test/CodeGen/X86/pseudo_cmov_lower2.ll | 50 +++++++++++++++++++++
 2 files changed, 65 insertions(+), 4 deletions(-)

diff --git a/llvm/lib/Target/X86/X86ISelLowering.cpp b/llvm/lib/Target/X86/X86ISelLowering.cpp
index 7e6ec0ea5d06..fa18985e4f8c 100644
--- a/llvm/lib/Target/X86/X86ISelLowering.cpp
+++ b/llvm/lib/Target/X86/X86ISelLowering.cpp
@@ -28814,20 +28814,21 @@ X86TargetLowering::EmitLoweredSelect(MachineInstr &MI,
   X86::CondCode CC = X86::CondCode(MI.getOperand(3).getImm());
   X86::CondCode OppCC = X86::GetOppositeBranchCondition(CC);
   MachineInstr *LastCMOV = &MI;
-  MachineBasicBlock::iterator NextMIIt =
-      std::next(MachineBasicBlock::iterator(MI));
+  MachineBasicBlock::iterator NextMIIt = MachineBasicBlock::iterator(MI);
 
   // Check for case 1, where there are multiple CMOVs with the same condition
   // first.  Of the two cases of multiple CMOV lowerings, case 1 reduces the
   // number of jumps the most.
 
   if (isCMOVPseudo(MI)) {
-    // See if we have a string of CMOVS with the same condition.
+    // See if we have a string of CMOVS with the same condition. Skip over
+    // intervening debug insts.
     while (NextMIIt != ThisMBB->end() && isCMOVPseudo(*NextMIIt) &&
            (NextMIIt->getOperand(3).getImm() == CC ||
             NextMIIt->getOperand(3).getImm() == OppCC)) {
       LastCMOV = &*NextMIIt;
       ++NextMIIt;
+      NextMIIt = skipDebugInstructionsForward(NextMIIt, ThisMBB->end());
     }
   }
 
@@ -28859,8 +28860,18 @@ X86TargetLowering::EmitLoweredSelect(MachineInstr &MI,
     SinkMBB->addLiveIn(X86::EFLAGS);
   }
 
+  // Transfer any debug instructions inside the CMOV sequence to the sunk block.
+  auto DbgEnd = MachineBasicBlock::iterator(LastCMOV);
+  auto DbgIt = MachineBasicBlock::iterator(MI);
+  while (DbgIt != DbgEnd) {
+    auto Next = std::next(DbgIt);
+    if (DbgIt->isDebugInstr())
+      SinkMBB->push_back(DbgIt->removeFromParent());
+    DbgIt = Next;
+  }
+
   // Transfer the remainder of ThisMBB and its successor edges to SinkMBB.
-  SinkMBB->splice(SinkMBB->begin(), ThisMBB,
+  SinkMBB->splice(SinkMBB->end(), ThisMBB,
                   std::next(MachineBasicBlock::iterator(LastCMOV)),
                   ThisMBB->end());
   SinkMBB->transferSuccessorsAndUpdatePHIs(ThisMBB);
diff --git a/llvm/test/CodeGen/X86/pseudo_cmov_lower2.ll b/llvm/test/CodeGen/X86/pseudo_cmov_lower2.ll
index 5218e1f0cee9..e0370534239b 100644
--- a/llvm/test/CodeGen/X86/pseudo_cmov_lower2.ll
+++ b/llvm/test/CodeGen/X86/pseudo_cmov_lower2.ll
@@ -210,4 +210,54 @@ entry:
   ret double %d6
 }
 
+declare void @llvm.dbg.value(metadata, metadata, metadata)
+
+; Like the test for @foo1, but check that the inserted dbg.value does not
+; affect codegen. The CHECK items below should always be identical to @foo1,
+; minus the DEBUG_VALUE line and changes in labels..
+define double @foo1_g(float %p1, double %p2, double %p3) nounwind !dbg !4 {
+; CHECK-LABEL: foo1_g:
+; CHECK:       # %bb.0: # %entry
+; CHECK-NEXT:    xorps %xmm3, %xmm3
+; CHECK-NEXT:    ucomiss %xmm3, %xmm0
+; CHECK-NEXT:    movsd {{.*#+}} xmm0 = mem[0],zero
+; CHECK-NEXT:    jae .LBB6_1
+; CHECK-NEXT:  # %bb.2: # %entry
+; CHECK-NEXT:    addsd %xmm2, %xmm0
+; CHECK-NEXT:    jmp .LBB6_3
+; CHECK-NEXT:  .LBB6_1:
+; CHECK-NEXT:    addsd %xmm0, %xmm1
+; CHECK-NEXT:    movapd %xmm1, %xmm0
+; CHECK-NEXT:    movapd %xmm1, %xmm2
+; CHECK-NEXT:  .LBB6_3: # %entry
+; CHECK-NEXT:    #DEBUG_VALUE: foobar:xyzzy <- undef
+; CHECK-NEXT:    subsd %xmm1, %xmm0
+; CHECK-NEXT:    addsd %xmm2, %xmm0
+; CHECK-NEXT:    retq
+entry:
+  %c1 = fcmp oge float %p1, 0.000000e+00
+  %d0 = fadd double %p2, 1.25e0
+  %d1 = fadd double %p3, 1.25e0
+  %d2 = select i1 %c1, double %d0, double %d1
+  call void @llvm.dbg.value(metadata float undef, metadata !5, metadata !DIExpression()), !dbg !6
+  %d3 = select i1 %c1, double %d2, double %p2
+  %d4 = select i1 %c1, double %d3, double %p3
+  %d5 = fsub double %d2, %d3
+  %d6 = fadd double %d5, %d4
+  ret double %d6
+}
+
+!llvm.module.flags = !{!1}
+!llvm.dbg.cu = !{!2}
+
 !0 = !{!"branch_weights", i32 1, i32 2000}
+!1 = !{i32 2, !"Debug Info Version", i32 3}
+!2 = distinct !DICompileUnit(language: DW_LANG_C99, file: !3, producer: "clang", isOptimized: true, runtimeVersion: 0, emissionKind: FullDebug, nameTableKind: None)
+!3 = !DIFile(filename: "test.c", directory: ".")
+!4 = distinct !DISubprogram(name: "foobar", scope: !2, file: !3, line: 1, type: !9, scopeLine: 3, flags: DIFlagPrototyped, spFlags: DISPFlagDefinition | DISPFlagOptimized, unit: !2, retainedNodes: !8)
+!5 = !DILocalVariable(name: "xyzzy", scope: !4, file: !3, line: 2, type: !7)
+!6 = !DILocation(line: 1, column: 1, scope: !4)
+!7 = !DIBasicType(name: "float", size: 32, encoding: DW_ATE_float)
+!8 = !{!5}
+!9 = !DISubroutineType(types: !10)
+!10 = !{!7}