[llvm] r304050 - [GVN] Recommit the patch "Add phi-translate support in scalarpre".

[Wei Mi via llvm-commits]

That is great. Thanks. However for now we still need the patch for
partially redundent case. I already fixed the bug and did some more
testing and will recommit it soon.

On Wed, Jun 7, 2017 at 1:25 AM, Daniel Berlin <dberlin at dberlin.org> wrote:
>
>
> On Fri, May 26, 2017 at 5:54 PM, Wei Mi via llvm-commits
> <llvm-commits at lists.llvm.org> wrote:
>>
>> Author: wmi
>> Date: Fri May 26 19:54:19 2017
>> New Revision: 304050
>>
>> URL: http://llvm.org/viewvc/llvm-project?rev=304050&view=rev
>> Log:
>> [GVN] Recommit the patch "Add phi-translate support in scalarpre".
>>
>> The recommit is to fix a bug about ExtractValue and InsertValue ops. For
>> those
>> ops, some varargs inside GVN::Expression are not value numbers but raw
>> index
>> numbers. It is wrong to do phi-translate for raw index numbers, and the
>> fix is
>> to stop doing that.
>>
>> Right now scalarpre doesn't have phi-translate support, so it will miss
>> some
>> simple pre opportunities. Like the following testcase, current scalarpre
>> cannot
>> recognize the last "a * b" is fully redundent because a and b used by the
>> last
>> "a * b" expr are both defined by phis.
>>
>> long a[100], b[100], g1, g2, g3;
>> __attribute__((pure)) long goo();
>>
>> void foo(long a, long b, long c, long d) {
>>   g1 = a * b;
>>   if (__builtin_expect(g2 > 3, 0)) {
>>     a = c;
>>     b = d;
>>     g2 = a * b;
>>   }
>>   g3 = a * b;      // fully redundant.
>> }
>> The patch adds phi-translate support in scalarpre. This is only a
>> temporary
>> solution before the newpre based on newgvn is available.
>
>
> Just to mention:
> NewGVN does not require PRE to get the case above.
> It already gets it :)
>
> In general, any full redundancy that exists in the program will be caught by
> newgvn, as it is complete.
> (those where it doesn't are deliberate decisions we could change :P)
>
> before -newgvn:
> target datalayout = "e-m:o-i64:64-f80:128-n8:16:32:64-S128"
> target triple = "x86_64-apple-macosx10.12.0"
>
> @g1 = common global i64 0, align 8
> @g2 = common global i64 0, align 8
> @g3 = common global i64 0, align 8
> @a = common global [100 x i64] zeroinitializer, align 16
> @b = common global [100 x i64] zeroinitializer, align 16
>
> ; Function Attrs: nounwind ssp uwtable
> define void @foo(i64, i64, i64, i64) #0 {
>   %5 = mul nsw i64 %0, %1
>   store i64 %5, i64* @g1, align 8, !tbaa !2
>   %6 = load i64, i64* @g2, align 8, !tbaa !2
>   %7 = icmp sgt i64 %6, 3
>   %8 = zext i1 %7 to i32
>   %9 = sext i32 %8 to i64
>   %10 = call i64 @llvm.expect.i64(i64 %9, i64 0)
>   %11 = icmp ne i64 %10, 0
>   br i1 %11, label %12, label %14
>
> ; <label>:12:                                     ; preds = %4
>   %13 = mul nsw i64 %2, %3
>   store i64 %13, i64* @g2, align 8, !tbaa !2
>   br label %14
>
> ; <label>:14:                                     ; preds = %12, %4
>   %.08 = phi i64 [ %3, %12 ], [ %1, %4 ]
>   %.0 = phi i64 [ %2, %12 ], [ %0, %4 ]
>   %15 = mul nsw i64 %.0, %.08
>   store i64 %15, i64* @g3, align 8, !tbaa !2
>   ret void
> }
>
> after -newgvn:
> target datalayout = "e-m:o-i64:64-f80:128-n8:16:32:64-S128"
> target triple = "x86_64-apple-macosx10.12.0"
>
> @g1 = common global i64 0, align 8
> @g2 = common global i64 0, align 8
> @g3 = common global i64 0, align 8
> @a = common global [100 x i64] zeroinitializer, align 16
> @b = common global [100 x i64] zeroinitializer, align 16
>
> ; Function Attrs: nounwind ssp uwtable
> define void @foo(i64, i64, i64, i64) #0 {
>   %5 = mul nsw i64 %0, %1
>   store i64 %5, i64* @g1, align 8, !tbaa !2
>   %6 = load i64, i64* @g2, align 8, !tbaa !2
>   %7 = icmp sgt i64 %6, 3
>   %8 = zext i1 %7 to i32
>   %9 = sext i32 %8 to i64
>   %10 = call i64 @llvm.expect.i64(i64 %9, i64 0)
>   %11 = icmp ne i64 %10, 0
>   br i1 %11, label %12, label %14
>
> ; <label>:12:                                     ; preds = %4
>   %13 = mul nsw i64 %2, %3
>   store i64 %13, i64* @g2, align 8, !tbaa !2
>   br label %14
>
> ; <label>:14:                                     ; preds = %12, %4
>   %15 = phi i64 [ %13, %12 ], [ %5, %4 ]
>   %.08 = phi i64 [ %3, %12 ], [ %1, %4 ]
>   %.0 = phi i64 [ %2, %12 ], [ %0, %4 ]
>   store i64 %15, i64* @g3, align 8, !tbaa !2
>   ret void
> }
>
> (note that %15 has been transformed into a phi of the existing values)
>
>