[PATCH] D43451: [ARM] Mark -1 as cheap in xor's for thumb1

[Dave Green via Phabricator via llvm-commits]

dmgreen updated this revision to Diff 134945.
dmgreen added a comment.

I realised I could just show the updates here without having to commit the changes first. So that's what this is.

I've not committed the left hand side yet, let me know if I should anyway. Otherwise this should show the differences.


https://reviews.llvm.org/D43451

Files:
  lib/Target/ARM/ARMTargetTransformInfo.cpp
  test/CodeGen/Thumb/mvn.ll


Index: test/CodeGen/Thumb/mvn.ll
===================================================================
--- test/CodeGen/Thumb/mvn.ll
+++ test/CodeGen/Thumb/mvn.ll
@@ -61,21 +61,20 @@
 
 define void @loop8_2(i8* %a, i8* %b) {
 ; CHECK-LABEL: loop8_2:
-; CHECK:         .save {r4, r5, r7, lr}
-; CHECK-NEXT:    push {r4, r5, r7, lr}
+; CHECK:         .save {r4, lr}
+; CHECK-NEXT:    push {r4, lr}
 ; CHECK-NEXT:    movs r2, #0
-; CHECK-NEXT:    movs r3, #255
 ; CHECK-NEXT:  .LBB3_1:
-; CHECK-NEXT:    ldrb r4, [r1, r2]
-; CHECK-NEXT:    ldrb r5, [r0, r2]
-; CHECK-NEXT:    eors r5, r3
-; CHECK-NEXT:    strb r5, [r0, r2]
-; CHECK-NEXT:    eors r4, r3
-; CHECK-NEXT:    strb r4, [r1, r2]
+; CHECK-NEXT:    ldrb r3, [r1, r2]
+; CHECK-NEXT:    ldrb r4, [r0, r2]
+; CHECK-NEXT:    mvns r4, r4
+; CHECK-NEXT:    strb r4, [r0, r2]
+; CHECK-NEXT:    mvns r3, r3
+; CHECK-NEXT:    strb r3, [r1, r2]
 ; CHECK-NEXT:    adds r2, r2, #1
 ; CHECK-NEXT:    cmp r2, #10
 ; CHECK-NEXT:    bne .LBB3_1
-; CHECK-NEXT:    pop {r4, r5, r7, pc}
+; CHECK-NEXT:    pop {r4, pc}
 entry:
   br label %for.body
 
@@ -157,21 +156,20 @@
 
 define void @loop32_2(i32* %a, i32* %b) {
 ; CHECK-LABEL: loop32_2:
-; CHECK:         .save {r4, r5, r7, lr}
-; CHECK-NEXT:    push {r4, r5, r7, lr}
+; CHECK:         .save {r4, lr}
+; CHECK-NEXT:    push {r4, lr}
 ; CHECK-NEXT:    movs r2, #0
-; CHECK-NEXT:    mvns r3, r2
 ; CHECK-NEXT:  .LBB7_1:
-; CHECK-NEXT:    ldr r4, [r1, r2]
-; CHECK-NEXT:    ldr r5, [r0, r2]
-; CHECK-NEXT:    eors r5, r3
-; CHECK-NEXT:    str r5, [r0, r2]
-; CHECK-NEXT:    eors r4, r3
-; CHECK-NEXT:    str r4, [r1, r2]
+; CHECK-NEXT:    ldr r3, [r1, r2]
+; CHECK-NEXT:    ldr r4, [r0, r2]
+; CHECK-NEXT:    mvns r4, r4
+; CHECK-NEXT:    str r4, [r0, r2]
+; CHECK-NEXT:    mvns r3, r3
+; CHECK-NEXT:    str r3, [r1, r2]
 ; CHECK-NEXT:    adds r2, r2, #4
 ; CHECK-NEXT:    cmp r2, #40
 ; CHECK-NEXT:    bne .LBB7_1
-; CHECK-NEXT:    pop {r4, r5, r7, pc}
+; CHECK-NEXT:    pop {r4, pc}
 entry:
   br label %for.body
 
Index: lib/Target/ARM/ARMTargetTransformInfo.cpp
===================================================================
--- lib/Target/ARM/ARMTargetTransformInfo.cpp
+++ lib/Target/ARM/ARMTargetTransformInfo.cpp
@@ -126,6 +126,13 @@
       return 0;
   }
 
+  // xor a, -1 can always be folded to MVN
+  if (Opcode == Instruction::Xor) {
+    int64_t NegImm = Imm.getSExtValue();
+    if (NegImm == -1)
+      return 0;
+  }
+
   return getIntImmCost(Imm, Ty);
 }
 


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