[X86] Don't convert 8 or 16 bit ADDs to LEAs on Atom in FixupLEAPass.

We use the functions that convert to three address to do the
conversion, but changing an 8 or 16 bit will cause it to create
a virtual register. This can't be done after register allocation
where this pass runs.

I've switched the pass completely to a white list of instructions
that can be converted to LEA instead of a blacklist that was
incorrect. This will avoid surprises if we enhance the three
address conversion function to include additional instructions
in the future.

Fixes PR42565.

llvm-svn: 365720

1 files changed, 15 insertions, 12 deletions

diff --git a/llvm/lib/Target/X86/X86FixupLEAs.cpp b/llvm/lib/Target/X86/X86FixupLEAs.cpp
index 60f70ad1059..041529a0be6 100644
--- a/llvm/lib/Target/X86/X86FixupLEAs.cpp
+++ b/llvm/lib/Target/X86/X86FixupLEAs.cpp
@@ -149,6 +149,9 @@ FixupLEAPass::postRAConvertToLEA(MachineBasicBlock &MBB,
     return nullptr;
 
   switch (MI.getOpcode()) {
+  default:
+    // Only convert instructions that we've verified are safe.
+    return nullptr;
   case X86::ADD64ri32:
   case X86::ADD64ri8:
   case X86::ADD64ri32_DB:
@@ -157,24 +160,24 @@ FixupLEAPass::postRAConvertToLEA(MachineBasicBlock &MBB,
   case X86::ADD32ri8:
   case X86::ADD32ri_DB:
   case X86::ADD32ri8_DB:
-  case X86::ADD16ri:
-  case X86::ADD16ri8:
-  case X86::ADD16ri_DB:
-  case X86::ADD16ri8_DB:
     if (!MI.getOperand(2).isImm()) {
       // convertToThreeAddress will call getImm()
       // which requires isImm() to be true
       return nullptr;
     }
     break;
-  case X86::ADD16rr:
-  case X86::ADD16rr_DB:
-    if (MI.getOperand(1).getReg() != MI.getOperand(2).getReg()) {
-      // if src1 != src2, then convertToThreeAddress will
-      // need to create a Virtual register, which we cannot do
-      // after register allocation.
-      return nullptr;
-    }
+  case X86::SHL64ri:
+  case X86::SHL32ri:
+  case X86::INC64r:
+  case X86::INC32r:
+  case X86::DEC64r:
+  case X86::DEC32r:
+  case X86::ADD64rr:
+  case X86::ADD64rr_DB:
+  case X86::ADD32rr:
+  case X86::ADD32rr_DB:
+    // These instructions are all fine to convert.
+    break;
   }
   MachineFunction::iterator MFI = MBB.getIterator();
   return TII->convertToThreeAddress(MFI, MI, nullptr);