[SystemZ] Check for legality before doing LOAD AND TEST transformations.

Since a load and test instruction treat its operands as signed, it can only
replace a logical compare for EQ/NE uses.

Review: Ulrich Weigand
https://bugs.llvm.org/show_bug.cgi?id=35662

llvm-svn: 322161

1 files changed, 25 insertions, 15 deletions

diff --git a/llvm/lib/Target/SystemZ/SystemZElimCompare.cpp b/llvm/lib/Target/SystemZ/SystemZElimCompare.cpp
index a8e0ba4fb15..0619a47a14d 100644
--- a/llvm/lib/Target/SystemZ/SystemZElimCompare.cpp
+++ b/llvm/lib/Target/SystemZ/SystemZElimCompare.cpp
@@ -86,9 +86,11 @@ private:
                      SmallVectorImpl<MachineInstr *> &CCUsers);
   bool convertToLoadAndTrap(MachineInstr &MI, MachineInstr &Compare,
                             SmallVectorImpl<MachineInstr *> &CCUsers);
-  bool convertToLoadAndTest(MachineInstr &MI);
+  bool convertToLoadAndTest(MachineInstr &MI, MachineInstr &Compare,
+                            SmallVectorImpl<MachineInstr *> &CCUsers);
   bool adjustCCMasksForInstr(MachineInstr &MI, MachineInstr &Compare,
-                             SmallVectorImpl<MachineInstr *> &CCUsers);
+                             SmallVectorImpl<MachineInstr *> &CCUsers,
+                             unsigned ConvOpc = 0);
   bool optimizeCompareZero(MachineInstr &Compare,
                            SmallVectorImpl<MachineInstr *> &CCUsers);
   bool fuseCompareOperations(MachineInstr &Compare,
@@ -282,9 +284,13 @@ bool SystemZElimCompare::convertToLoadAndTrap(
 
 // If MI is a load instruction, try to convert it into a LOAD AND TEST.
 // Return true on success.
-bool SystemZElimCompare::convertToLoadAndTest(MachineInstr &MI) {
+bool SystemZElimCompare::convertToLoadAndTest(
+    MachineInstr &MI, MachineInstr &Compare,
+    SmallVectorImpl<MachineInstr *> &CCUsers) {
+
+  // Try to adjust CC masks for a LOAD AND TEST opcode that could replace MI.
   unsigned Opcode = TII->getLoadAndTest(MI.getOpcode());
-  if (!Opcode)
+  if (!Opcode || !adjustCCMasksForInstr(MI, Compare, CCUsers, Opcode))
     return false;
 
   MI.setDesc(TII->get(Opcode));
@@ -294,14 +300,16 @@ bool SystemZElimCompare::convertToLoadAndTest(MachineInstr &MI) {
 }
 
 // The CC users in CCUsers are testing the result of a comparison of some
-// value X against zero and we know that any CC value produced by MI
-// would also reflect the value of X.  Try to adjust CCUsers so that
-// they test the result of MI directly, returning true on success.
-// Leave everything unchanged on failure.
+// value X against zero and we know that any CC value produced by MI would
+// also reflect the value of X.  ConvOpc may be used to pass the transfomed
+// opcode MI will have if this succeeds.  Try to adjust CCUsers so that they
+// test the result of MI directly, returning true on success.  Leave
+// everything unchanged on failure.
 bool SystemZElimCompare::adjustCCMasksForInstr(
     MachineInstr &MI, MachineInstr &Compare,
-    SmallVectorImpl<MachineInstr *> &CCUsers) {
-  int Opcode = MI.getOpcode();
+    SmallVectorImpl<MachineInstr *> &CCUsers,
+    unsigned ConvOpc) {
+  int Opcode = (ConvOpc ? ConvOpc : MI.getOpcode());
   const MCInstrDesc &Desc = TII->get(Opcode);
   unsigned MIFlags = Desc.TSFlags;
 
@@ -358,9 +366,11 @@ bool SystemZElimCompare::adjustCCMasksForInstr(
   }
 
   // CC is now live after MI.
-  int CCDef = MI.findRegisterDefOperandIdx(SystemZ::CC, false, true, TRI);
-  assert(CCDef >= 0 && "Couldn't find CC set");
-  MI.getOperand(CCDef).setIsDead(false);
+  if (!ConvOpc) {
+    int CCDef = MI.findRegisterDefOperandIdx(SystemZ::CC, false, true, TRI);
+    assert(CCDef >= 0 && "Couldn't find CC set");
+    MI.getOperand(CCDef).setIsDead(false);
+  }
 
   // Clear any intervening kills of CC.
   MachineBasicBlock::iterator MBBI = MI, MBBE = Compare;
@@ -419,7 +429,7 @@ bool SystemZElimCompare::optimizeCompareZero(
         }
       }
       // Try to eliminate Compare by reusing a CC result from MI.
-      if ((!CCRefs && convertToLoadAndTest(MI)) ||
+      if ((!CCRefs && convertToLoadAndTest(MI, Compare, CCUsers)) ||
           (!CCRefs.Def && adjustCCMasksForInstr(MI, Compare, CCUsers))) {
         EliminatedComparisons += 1;
         return true;
@@ -441,7 +451,7 @@ bool SystemZElimCompare::optimizeCompareZero(
     MachineInstr &MI = *MBBI;
     if (preservesValueOf(MI, SrcReg)) {
       // Try to eliminate Compare by reusing a CC result from MI.
-      if (convertToLoadAndTest(MI)) {
+      if (convertToLoadAndTest(MI, Compare, CCUsers)) {
         EliminatedComparisons += 1;
         return true;
       }