[PATCH] ARM: When re-creating a branch via InsertBranch, preserve CPSR flags.

[Peter Collingbourne]

Hi t.p.northover,

In particular, this preserves the kill flag, which allows the Thumb2 cbn?z
optimization to be applied in cases where a branch has been re-created after
the live variables analysis pass, e.g. by the machine block placement pass.

This appears to be low risk; a number of other targets seem to already be
doing something similar, e.g. AArch64, PowerPC.

http://reviews.llvm.org/D9184

Files:
  lib/Target/ARM/ARMBaseInstrInfo.cpp
  test/CodeGen/ARM/sjlj-prepare-critical-edge.ll
  test/CodeGen/Thumb2/v8_IT_5.ll

Index: lib/Target/ARM/ARMBaseInstrInfo.cpp
===================================================================
--- lib/Target/ARM/ARMBaseInstrInfo.cpp
+++ lib/Target/ARM/ARMBaseInstrInfo.cpp
@@ -410,21 +410,23 @@
   assert((Cond.size() == 2 || Cond.size() == 0) &&
          "ARM branch conditions have two components!");
 
+  // For conditional branches, we use addOperand to preserve CPSR flags.
+
   if (!FBB) {
     if (Cond.empty()) { // Unconditional branch?
       if (isThumb)
         BuildMI(&MBB, DL, get(BOpc)).addMBB(TBB).addImm(ARMCC::AL).addReg(0);
       else
         BuildMI(&MBB, DL, get(BOpc)).addMBB(TBB);
     } else
       BuildMI(&MBB, DL, get(BccOpc)).addMBB(TBB)
-        .addImm(Cond[0].getImm()).addReg(Cond[1].getReg());
+        .addImm(Cond[0].getImm()).addOperand(Cond[1]);
     return 1;
   }
 
   // Two-way conditional branch.
   BuildMI(&MBB, DL, get(BccOpc)).addMBB(TBB)
-    .addImm(Cond[0].getImm()).addReg(Cond[1].getReg());
+    .addImm(Cond[0].getImm()).addOperand(Cond[1]);
   if (isThumb)
     BuildMI(&MBB, DL, get(BOpc)).addMBB(FBB).addImm(ARMCC::AL).addReg(0);
   else
Index: test/CodeGen/ARM/sjlj-prepare-critical-edge.ll
===================================================================
--- test/CodeGen/ARM/sjlj-prepare-critical-edge.ll
+++ test/CodeGen/ARM/sjlj-prepare-critical-edge.ll
@@ -79,7 +79,7 @@
 ; CHECK: str r0, [sp, [[OFFSET:#[0-9]+]]]
 ; CHECK: ldr [[R0:r[0-9]+]], [sp, [[OFFSET]]]
 ; CHECK: {{.*}}@ %do.body.i.i.i
-; CHECK: cmp [[R0]], #0
+; CHECK: cbz [[R0]]
 
 %"class.std::__1::basic_string" = type { %"class.std::__1::__compressed_pair" }
 %"class.std::__1::__compressed_pair" = type { %"class.std::__1::__libcpp_compressed_pair_imp" }
Index: test/CodeGen/Thumb2/v8_IT_5.ll
===================================================================
--- test/CodeGen/Thumb2/v8_IT_5.ll
+++ test/CodeGen/Thumb2/v8_IT_5.ll
@@ -3,8 +3,7 @@
 ; CHECK: it	ne
 ; CHECK-NEXT: cmpne
 ; CHECK-NEXT: bne [[JUMPTARGET:.LBB[0-9]+_[0-9]+]]
-; CHECK: cmp
-; CHECK-NEXT: beq
+; CHECK: cbz
 ; CHECK-NEXT: %if.else163
 ; CHECK-NEXT: mov.w
 ; CHECK-NEXT: b

EMAIL PREFERENCES
  http://reviews.llvm.org/settings/panel/emailpreferences/
-------------- next part --------------
A non-text attachment was scrubbed...
Name: D9184.24195.patch
Type: text/x-patch
Size: 2100 bytes
Desc: not available
URL: <http://lists.llvm.org/pipermail/llvm-commits/attachments/20150422/a8ee99ee/attachment.bin>