[WebAssembly] Use SelectionDAG::getUNDEF. NFC.

[oota-llvm.git] / lib / Target / X86 / X86InstrInfo.cpp

diff --git a/lib/Target/X86/X86InstrInfo.cpp b/lib/Target/X86/X86InstrInfo.cpp
index 04b68cd509fb36c30f3334b011116fb5d5c611d1..e9d36f8ce2f11a12ef2664cbe580eeedda4a8cdc 100644 (file)
--- a/lib/Target/X86/X86InstrInfo.cpp
+++ b/lib/Target/X86/X86InstrInfo.cpp
@@ -4412,9 +4412,19 @@ void X86InstrInfo::copyPhysReg(MachineBasicBlock &MBB,
     int Pop = is64 ? X86::POP64r : X86::POP32r;
     int AX = is64 ? X86::RAX : X86::EAX;
 
-    bool AXDead = (Reg == AX) ||
-                  (MachineBasicBlock::LQR_Dead ==
-                   MBB.computeRegisterLiveness(&getRegisterInfo(), AX, MI));
+    bool AXDead = (Reg == AX);
+    // FIXME: The above could figure out that AX is dead in more cases with:
+    //          || (MachineBasicBlock::LQR_Dead ==
+    //            MBB.computeRegisterLiveness(&getRegisterInfo(), AX, MI));
+    //
+    //        Unfortunately this is slightly broken, see PR24535 and the likely
+    //        related PR25033 PR24991 PR24992 PR25201. These issues seem to
+    //        showcase sub-register / super-register confusion: a previous kill
+    //        of AH but no kill of AL leads computeRegisterLiveness to
+    //        erroneously conclude that AX is dead.
+    //
+    //        Once fixed, also update cmpxchg-clobber-flags.ll and
+    //        peephole-na-phys-copy-folding.ll.
 
     if (!AXDead)
       BuildMI(MBB, MI, DL, get(Push)).addReg(AX, getKillRegState(true));
@@ -6715,16 +6725,16 @@ static const uint16_t ReplaceableInstrsAVX2[][3] = {
 // domains, but they require a bit more work than just switching opcodes.
 
 static const uint16_t *lookup(unsigned opcode, unsigned domain) {
-  for (unsigned i = 0, e = array_lengthof(ReplaceableInstrs); i != e; ++i)
-    if (ReplaceableInstrs[i][domain-1] == opcode)
-      return ReplaceableInstrs[i];
+  for (const uint16_t (&Row)[3] : ReplaceableInstrs)
+    if (Row[domain-1] == opcode)
+      return Row;
   return nullptr;
 }
 
 static const uint16_t *lookupAVX2(unsigned opcode, unsigned domain) {
-  for (unsigned i = 0, e = array_lengthof(ReplaceableInstrsAVX2); i != e; ++i)
-    if (ReplaceableInstrsAVX2[i][domain-1] == opcode)
-      return ReplaceableInstrsAVX2[i];
+  for (const uint16_t (&Row)[3] : ReplaceableInstrsAVX2)
+    if (Row[domain-1] == opcode)
+      return Row;
   return nullptr;
 }