Do not issue identity copies.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@52373 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/lib/CodeGen/LowerSubregs.cpp b/lib/CodeGen/LowerSubregs.cpp
index 0710a3530068165bee671839f021a646d6698ace..296e6d45c34eb1750ef360fa72321ded9f39dc91 100644 (file)
--- a/lib/CodeGen/LowerSubregs.cpp
+++ b/lib/CodeGen/LowerSubregs.cpp
@@ -108,15 +108,20 @@ bool LowerSubregsInstructionPass::LowerSubregToReg(MachineInstr *MI) {
 
   DOUT << "subreg: CONVERTING: " << *MI;
 
-  // Insert sub-register copy
-  const TargetRegisterClass *TRC0 = TRI.getPhysicalRegisterRegClass(DstSubReg);
-  const TargetRegisterClass *TRC1 = TRI.getPhysicalRegisterRegClass(InsReg);
-  TII.copyRegToReg(*MBB, MI, DstSubReg, InsReg, TRC0, TRC1);
+  if (DstSubReg == InsReg) {
+    // No need to insert an identify copy instruction.
+    DOUT << "subreg: eliminated!";
+  } else {
+    // Insert sub-register copy
+    const TargetRegisterClass *TRC0= TRI.getPhysicalRegisterRegClass(DstSubReg);
+    const TargetRegisterClass *TRC1= TRI.getPhysicalRegisterRegClass(InsReg);
+    TII.copyRegToReg(*MBB, MI, DstSubReg, InsReg, TRC0, TRC1);
 
 #ifndef NDEBUG
-  MachineBasicBlock::iterator dMI = MI;
-  DOUT << "subreg: " << *(--dMI);
+    MachineBasicBlock::iterator dMI = MI;
+    DOUT << "subreg: " << *(--dMI);
 #endif
+  }
 
   DOUT << "\n";
   MBB->remove(MI);
@@ -149,15 +154,19 @@ bool LowerSubregsInstructionPass::LowerInsert(MachineInstr *MI) {
 
   DOUT << "subreg: CONVERTING: " << *MI;
 
-  // Insert sub-register copy
-  const TargetRegisterClass *TRC0 = TRI.getPhysicalRegisterRegClass(DstSubReg);
-  const TargetRegisterClass *TRC1 = TRI.getPhysicalRegisterRegClass(InsReg);
-  TII.copyRegToReg(*MBB, MI, DstSubReg, InsReg, TRC0, TRC1);
-
+  if (DstSubReg == InsReg) {
+    // No need to insert an identify copy instruction.
+    DOUT << "subreg: eliminated!";
+  } else {
+    // Insert sub-register copy
+    const TargetRegisterClass *TRC0= TRI.getPhysicalRegisterRegClass(DstSubReg);
+    const TargetRegisterClass *TRC1= TRI.getPhysicalRegisterRegClass(InsReg);
+    TII.copyRegToReg(*MBB, MI, DstSubReg, InsReg, TRC0, TRC1);
 #ifndef NDEBUG
-  MachineBasicBlock::iterator dMI = MI;
-  DOUT << "subreg: " << *(--dMI);
+    MachineBasicBlock::iterator dMI = MI;
+    DOUT << "subreg: " << *(--dMI);
 #endif
+  }
 
   DOUT << "\n";
   MBB->remove(MI);

diff --git a/test/CodeGen/X86/2008-06-16-SubregsBug.ll b/test/CodeGen/X86/2008-06-16-SubregsBug.ll
new file mode 100644 (file)
index 0000000..75513b6
--- /dev/null
+++ b/test/CodeGen/X86/2008-06-16-SubregsBug.ll
@@ -0,0 +1,14 @@
+; RUN: llvm-as < %s | llc -mtriple=i386-apple-darwin | grep mov | count 4
+
+define i16 @test(i16* %tmp179) nounwind  {
+       %tmp180 = load i16* %tmp179, align 2            ; <i16> [#uses=2]
+       %tmp184 = and i16 %tmp180, -1024                ; <i16> [#uses=1]
+       %tmp186 = icmp eq i16 %tmp184, -32768           ; <i1> [#uses=1]
+       br i1 %tmp186, label %bb189, label %bb288
+
+bb189:         ; preds = %0
+       ret i16 %tmp180
+
+bb288:         ; preds = %0
+       ret i16 32
+}