ARM: Negative offset support problem (bug 20853 fix)

[ioblakov]

Summary

This patch is to permit a negative offset usage for a non frame access.

[t.p.northover]

Hi Igor,

I've just added the llvm-commits mailing list as a subscriber here. That's where all reviews take place in LLVM (even if we use this to help out).

I think the patch looks mostly fine, but the test is a bit odd: only the first 4 lines of the function actually seem to be tested, so we should either remove the rest or add CHECK lines for them.

Cheers.

Tim.

[rengolin]

test/CodeGen/ARM/negative-offset.ll

8

better to CHECK for the whole instruction, and to use regular expressions, and maybe add an extra CHECK-NOT on sub, to be explicit about the reason of this test.

;CHECK-LABEL: sum:
;CHECK-NOT: sub
;CHECK: ldr r{{.*}}, [r0, #-16]
;CHECK: ldr r{{.*}}, [r0, #-8]

14

returning this add should be more than enough.

[ioblakov]

New update with a minimal test

[rengolin]

Thanks Igor, LGTM.

Also, I ran the test-suite on ARM and all goes well.

Do you need help committing?

cheers,
--renato

[ioblakov]

Yes, the committing help is required. "rejected"/ Something is wrong.

[rengolin]

Committed in r217431.

Thanks!

lib/Target/ARM/ARMISelDAGToDAG.cpp

if (N.getOpcode() == ARMISD::Wrapper &&
       Base = N.getOperand(0);
     } else
       Base = N;
     OffImm  = CurDAG->getTargetConstant(0, MVT::i32);
     return true;
   }
 
   if (ConstantSDNode *RHS = dyn_cast<ConstantSDNode>(N.getOperand(1))) {
-    int RHSC = (int)RHS->getZExtValue();
+    int RHSC = (int)RHS->getSExtValue();
     if (N.getOpcode() == ISD::SUB)
       RHSC = -RHSC;
 
-    if (RHSC >= 0 && RHSC < 0x1000) { // 12 bits (unsigned)
+    if (RHSC > -0x1000 && RHSC < 0x1000) { // 12 bits
       Base   = N.getOperand(0);
       if (Base.getOpcode() == ISD::FrameIndex) {
         int FI = cast<FrameIndexSDNode>(Base)->getIndex();
         Base = CurDAG->getTargetFrameIndex(FI,
                                            getTargetLowering()->getPointerTy());
       }
       OffImm = CurDAG->getTargetConstant(RHSC, MVT::i32);
       return true;

test/CodeGen/ARM/negative-offset.ll

+; RUN: llc -mtriple=arm-eabi -O3 %s -o - | FileCheck %s
+
+; Function Attrs: nounwind readonly
+define arm_aapcscc i32 @sum(i32* nocapture readonly %p) #0 {
+entry:
+;CHECK-LABEL: sum:
+;CHECK-NOT: sub
+;CHECK: ldr r{{.*}}, [r0, #-16]
+;CHECK: ldr r{{.*}}, [r0, #-8]
+  %arrayidx = getelementptr inbounds i32* %p, i32 -4
+  %0 = load i32* %arrayidx, align 4
+  %arrayidx1 = getelementptr inbounds i32* %p, i32 -2
+  %1 = load i32* %arrayidx1, align 4
+  %add = add nsw i32 %1, %0
+  ret i32 %add
+}
+