[PATCH] D50222: [CodeGen] [SelectionDAG] More efficient code for X % C == 0
Krzysztof Parzyszek via Phabricator via llvm-commits
llvm-commits at lists.llvm.org
Fri Aug 3 12:34:12 PDT 2018
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
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