[llvm] [X86][PartialReduction] Lower zext-byte add reductions to vpsadbw (PR #201076)

[Simon Pilgrim via llvm-commits]

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@@ -0,0 +1,206 @@
+; RUN: llc < %s -mtriple=x86_64-unknown-unknown -mattr=+avx2 | FileCheck %s --check-prefix=NO-PSADBW
+
+; Negative CodeGen tests: must NOT lower to vpsadbw via tryByteSumReplacement.
+
+ at a = dso_local global [1024 x i8] zeroinitializer, align 16
+
+define dso_local i32 @byte_sum_v16_i32_sext() nounwind {
+; NO-PSADBW-LABEL: byte_sum_v16_i32_sext:
+entry:
+  br label %vector.body
+
+vector.body:
+  %index = phi i64 [ 0, %entry ], [ %index.next, %vector.body ]
+  %vec.phi = phi <16 x i32> [ zeroinitializer, %entry ], [ %add, %vector.body ]
+  %p = getelementptr inbounds [1024 x i8], ptr @a, i64 0, i64 %index
+  %wide.load = load <16 x i8>, ptr %p, align 16
+  %z = sext <16 x i8> %wide.load to <16 x i32>
+  %add = add nsw <16 x i32> %z, %vec.phi
+  %index.next = add i64 %index, 16
+  %cmp = icmp eq i64 %index.next, 1024
+  br i1 %cmp, label %middle.block, label %vector.body
+
+middle.block:
+  %s1 = shufflevector <16 x i32> %add, <16 x i32> poison, <16 x i32> <i32 8, i32 9, i32 10, i32 11, i32 12, i32 13, i32 14, i32 15, i32 poison, i32 poison, i32 poison, i32 poison, i32 poison, i32 poison, i32 poison, i32 poison>
+  %r1 = add <16 x i32> %add, %s1
+  %s2 = shufflevector <16 x i32> %r1, <16 x i32> poison, <16 x i32> <i32 4, i32 5, i32 6, i32 7, i32 poison, i32 poison, i32 poison, i32 poison, i32 poison, i32 poison, i32 poison, i32 poison, i32 poison, i32 poison, i32 poison, i32 poison>
+  %r2 = add <16 x i32> %r1, %s2
+  %s3 = shufflevector <16 x i32> %r2, <16 x i32> poison, <16 x i32> <i32 2, i32 3, i32 poison, i32 poison, i32 poison, i32 poison, i32 poison, i32 poison, i32 poison, i32 poison, i32 poison, i32 poison, i32 poison, i32 poison, i32 poison, i32 poison>
+  %r3 = add <16 x i32> %r2, %s3
+  %s4 = shufflevector <16 x i32> %r3, <16 x i32> poison, <16 x i32> <i32 1, i32 poison, i32 poison, i32 poison, i32 poison, i32 poison, i32 poison, i32 poison, i32 poison, i32 poison, i32 poison, i32 poison, i32 poison, i32 poison, i32 poison, i32 poison>
+  %r4 = add <16 x i32> %r3, %s4
+  %ext = extractelement <16 x i32> %r4, i32 0
+  ret i32 %ext
+; NO-PSADBW-NOT: psadbw
+}
+
+;----------------------------------------------------------------------------
+; NEGATIVE: i16 source instead of i8.
+;
+; psadbw operates on bytes; widening from i16 is the wrong shape so the pass
+; must bail.  Nothing here looks like a SAD/MAdd either, so SDAG also will
+; not invent a psadbw.
+;----------------------------------------------------------------------------
+define dso_local i32 @word_sum_v16_i32(ptr nocapture readonly %src) nounwind {
+; NO-PSADBW-LABEL: word_sum_v16_i32:
+entry:
+  br label %vector.body
+
+vector.body:
+  %index = phi i64 [ 0, %entry ], [ %index.next, %vector.body ]
+  %vec.phi = phi <16 x i32> [ zeroinitializer, %entry ], [ %add, %vector.body ]
+  %p = getelementptr inbounds i16, ptr %src, i64 %index
+  %wide.load = load <16 x i16>, ptr %p, align 2
+  %z = zext <16 x i16> %wide.load to <16 x i32>
+  %add = add nsw <16 x i32> %z, %vec.phi
+  %index.next = add i64 %index, 16
+  %cmp = icmp eq i64 %index.next, 1024
+  br i1 %cmp, label %middle.block, label %vector.body
+
+middle.block:
+  %s1 = shufflevector <16 x i32> %add, <16 x i32> poison, <16 x i32> <i32 8, i32 9, i32 10, i32 11, i32 12, i32 13, i32 14, i32 15, i32 poison, i32 poison, i32 poison, i32 poison, i32 poison, i32 poison, i32 poison, i32 poison>
+  %r1 = add <16 x i32> %add, %s1
+  %s2 = shufflevector <16 x i32> %r1, <16 x i32> poison, <16 x i32> <i32 4, i32 5, i32 6, i32 7, i32 poison, i32 poison, i32 poison, i32 poison, i32 poison, i32 poison, i32 poison, i32 poison, i32 poison, i32 poison, i32 poison, i32 poison>
+  %r2 = add <16 x i32> %r1, %s2
+  %s3 = shufflevector <16 x i32> %r2, <16 x i32> poison, <16 x i32> <i32 2, i32 3, i32 poison, i32 poison, i32 poison, i32 poison, i32 poison, i32 poison, i32 poison, i32 poison, i32 poison, i32 poison, i32 poison, i32 poison, i32 poison, i32 poison>
+  %r3 = add <16 x i32> %r2, %s3
+  %s4 = shufflevector <16 x i32> %r3, <16 x i32> poison, <16 x i32> <i32 1, i32 poison, i32 poison, i32 poison, i32 poison, i32 poison, i32 poison, i32 poison, i32 poison, i32 poison, i32 poison, i32 poison, i32 poison, i32 poison, i32 poison, i32 poison>
+  %r4 = add <16 x i32> %r3, %s4
+  %ext = extractelement <16 x i32> %r4, i32 0
----------------
RKSimon wrote:

use a vector.reduce.add.v16i32 call here instead of the expanded codegen

https://github.com/llvm/llvm-project/pull/201076