[llvm-commits] [llvm] r160066 - in /llvm/trunk: lib/Target/X86/X86InstrInfo.cpp test/CodeGen/X86/jump_sign.ll

[Manman Ren]

Author: mren
Date: Wed Jul 11 14:35:12 2012
New Revision: 160066

URL: http://llvm.org/viewvc/llvm-project?rev=160066&view=rev
Log:
X86: Update to peephole optimization to move Movr0 before (Sub, Cmp) pair.

When Movr0 is between sub and cmp, we move Movr0 before sub if it enables
removal of Cmp.

Modified:
    llvm/trunk/lib/Target/X86/X86InstrInfo.cpp
    llvm/trunk/test/CodeGen/X86/jump_sign.ll

Modified: llvm/trunk/lib/Target/X86/X86InstrInfo.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Target/X86/X86InstrInfo.cpp?rev=160066&r1=160065&r2=160066&view=diff
==============================================================================
--- llvm/trunk/lib/Target/X86/X86InstrInfo.cpp (original)
+++ llvm/trunk/lib/Target/X86/X86InstrInfo.cpp Wed Jul 11 14:35:12 2012
@@ -3110,6 +3110,7 @@
       RE = CmpInstr->getParent() == MI->getParent() ?
            MachineBasicBlock::reverse_iterator(++Def) /* points to MI */ :
            CmpInstr->getParent()->rend();
+  MachineInstr *Movr0Inst = 0;
   for (; RI != RE; ++RI) {
     MachineInstr *Instr = &*RI;
     // Check whether CmpInstr can be made redundant by the current instruction.
@@ -3119,10 +3120,24 @@
     }
 
     if (Instr->modifiesRegister(X86::EFLAGS, TRI) ||
-        Instr->readsRegister(X86::EFLAGS, TRI))
+        Instr->readsRegister(X86::EFLAGS, TRI)) {
       // This instruction modifies or uses EFLAGS.
+
+      // MOV32r0 etc. are implemented with xor which clobbers condition code.
+      // They are safe to move up, if the definition to EFLAGS is dead and
+      // earlier instructions do not read or write EFLAGS.
+      if (!Movr0Inst && (Instr->getOpcode() == X86::MOV8r0 ||
+           Instr->getOpcode() == X86::MOV16r0 ||
+           Instr->getOpcode() == X86::MOV32r0 ||
+           Instr->getOpcode() == X86::MOV64r0) &&
+          Instr->registerDefIsDead(X86::EFLAGS, TRI)) {
+        Movr0Inst = Instr;
+        continue;
+      }
+
       // We can't remove CmpInstr.
       return false;
+    }
   }
 
   // Return false if no candidates exist.
@@ -3204,6 +3219,12 @@
         return false;
   }
 
+  // Move Movr0Inst to the place right before Sub.
+  if (Movr0Inst) {
+    Sub->getParent()->remove(Movr0Inst);
+    Sub->getParent()->insert(MachineBasicBlock::iterator(Sub), Movr0Inst);
+  }
+
   // Make sure Sub instruction defines EFLAGS.
   assert(Sub->getNumOperands() >= 4 && Sub->getOperand(3).isReg() &&
          Sub->getOperand(3).getReg() == X86::EFLAGS &&

Modified: llvm/trunk/test/CodeGen/X86/jump_sign.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/CodeGen/X86/jump_sign.ll?rev=160066&r1=160065&r2=160066&view=diff
==============================================================================
--- llvm/trunk/test/CodeGen/X86/jump_sign.ll (original)
+++ llvm/trunk/test/CodeGen/X86/jump_sign.ll Wed Jul 11 14:35:12 2012
@@ -137,6 +137,18 @@
   %add = add nsw i32 %sub, 1
   ret i32 %add
 }
+; rdar://11830760
+; When Movr0 is between sub and cmp, we need to move "Movr0" before sub.
+define i32 @l4(i32 %a, i32 %b) nounwind {
+entry:
+; CHECK: l4:
+; CHECK: sub
+; CHECK-NOT: cmp
+  %cmp = icmp sgt i32 %b, %a
+  %sub = sub i32 %a, %b
+  %.sub = select i1 %cmp, i32 0, i32 %sub
+  ret i32 %.sub
+}
 ; rdar://11540023
 define i32 @n(i32 %x, i32 %y) nounwind {
 entry: