AMDGPU: really don't commute REV opcodes if the target variant doesn't exist

If pseudoToMCOpcode failed, we would return the original opcode, so operands
would be swapped, but the instruction would remain the same.
It resulted in LSHLREV a, b ---> LSHLREV b, a.

This fixes Glamor text rendering and
piglit/arb_sample_shading-builtin-gl-sample-mask on VI.

This is a candidate for stable branches.

v2: the test was simplified by Tom Stellard
llvm-svn: 240824

1 files changed, 12 insertions, 8 deletions

diff --git a/llvm/lib/Target/AMDGPU/SIInstrInfo.cpp b/llvm/lib/Target/AMDGPU/SIInstrInfo.cpp
index 47bc17823b3..b517fb2f71c 100644
--- a/llvm/lib/Target/AMDGPU/SIInstrInfo.cpp
+++ b/llvm/lib/Target/AMDGPU/SIInstrInfo.cpp
@@ -440,22 +440,22 @@ SIInstrInfo::copyPhysReg(MachineBasicBlock &MBB,
   }
 }
 
-unsigned SIInstrInfo::commuteOpcode(const MachineInstr &MI) const {
+int SIInstrInfo::commuteOpcode(const MachineInstr &MI) const {
   const unsigned Opcode = MI.getOpcode();
 
   int NewOpc;
 
   // Try to map original to commuted opcode
   NewOpc = AMDGPU::getCommuteRev(Opcode);
-  // Check if the commuted (REV) opcode exists on the target.
-  if (NewOpc != -1 && pseudoToMCOpcode(NewOpc) != -1)
-    return NewOpc;
+  if (NewOpc != -1)
+    // Check if the commuted (REV) opcode exists on the target.
+    return pseudoToMCOpcode(NewOpc) != -1 ? NewOpc : -1;
 
   // Try to map commuted to original opcode
   NewOpc = AMDGPU::getCommuteOrig(Opcode);
-  // Check if the original (non-REV) opcode exists on the target.
-  if (NewOpc != -1 && pseudoToMCOpcode(NewOpc) != -1)
-    return NewOpc;
+  if (NewOpc != -1)
+    // Check if the original (non-REV) opcode exists on the target.
+    return pseudoToMCOpcode(NewOpc) != -1 ? NewOpc : -1;
 
   return Opcode;
 }
@@ -771,6 +771,10 @@ MachineInstr *SIInstrInfo::commuteInstruction(MachineInstr *MI,
   if (MI->getNumOperands() < 3)
     return nullptr;
 
+  int CommutedOpcode = commuteOpcode(*MI);
+  if (CommutedOpcode == -1)
+    return nullptr;
+
   int Src0Idx = AMDGPU::getNamedOperandIdx(MI->getOpcode(),
                                            AMDGPU::OpName::src0);
   assert(Src0Idx != -1 && "Should always have src0 operand");
@@ -833,7 +837,7 @@ MachineInstr *SIInstrInfo::commuteInstruction(MachineInstr *MI,
   }
 
   if (MI)
-    MI->setDesc(get(commuteOpcode(*MI)));
+    MI->setDesc(get(CommutedOpcode));
 
   return MI;
 }