[PATCH] D50222: [CodeGen] [SelectionDAG] More efficient code for X % C == 0

[Krzysztof Parzyszek via Phabricator via llvm-commits]

kparzysz added inline comments.


================
Comment at: test/CodeGen/Hexagon/swp-const-tc2.ll:9
 ; CHECK-NOT: loop0
-; CHECK: = mpy
-; CHECK-NOT: = mpy
+; CHECK: = memw
+; CHECK-NOT: = memw
----------------
hermord wrote:
> hermord wrote:
> > To the best of my understanding, it is valid to not perform the multiplication at all, since its can never be used because of the infinite loop at `b3`. This is the output I get:
> > 
> > 
> > ```
> > // %bb.0:                               // %b0
> > 	{
> > 		r0 = ##-1431655765
> > 	}
> > 	{
> > 		r0 = #0
> > 	}
> > 	{
> > 		r0 = memw(r0+#0)
> > 	}
> > 	.p2align	4
> > .LBB0_1:                                // %b3
> >                                         // =>This Inner Loop Header: Depth=1
> > 	{
> > 		jump .LBB0_1
> > 	}
> > ```
> *its result can never be used
Can you make these changes instead? 

```
-define void @f0() {
+define i32 @f0(i32* %a0) {
 b0:
   br label %b1
 
 b1:                                               ; preds = %b1, %b0
   %v0 = phi i32 [ 0, %b0 ], [ %v9, %b1 ]
   %v1 = phi i32 [ 0, %b0 ], [ %v8, %b1 ]
-  %v2 = load i32, i32* undef, align 4
+  %v2 = load i32, i32* %a0, align 4
   %v3 = add nsw i32 %v1, 1
   %v4 = srem i32 %v2, 3
   %v5 = icmp ne i32 %v4, 0
   %v6 = sub nsw i32 0, %v2
   %v7 = select i1 %v5, i32 %v6, i32 %v2
   %v8 = mul nsw i32 %v3, %v7
   %v9 = add nsw i32 %v0, 1
   %v10 = icmp eq i32 %v9, 1
   br i1 %v10, label %b2, label %b1
 
 b2:                                               ; preds = %b1
   %v11 = phi i32 [ %v8, %b1 ]
   br label %b3
 
 b3:                                               ; preds = %b3, %b2
-  br label %b3
+  ret i32 %v11
 }
```



Repository:
  rL LLVM

https://reviews.llvm.org/D50222