[llvm] f53f2a8 - [VectorCombine] Add constant splat handling for shuffleToIdentity (#92797)

[via llvm-commits]

Author: David Green
Date: 2024-05-28T10:55:57+01:00
New Revision: f53f2a8c92c6a66ef85a68686de224b6af3b47b4

URL: https://github.com/llvm/llvm-project/commit/f53f2a8c92c6a66ef85a68686de224b6af3b47b4
DIFF: https://github.com/llvm/llvm-project/commit/f53f2a8c92c6a66ef85a68686de224b6af3b47b4.diff

LOG: [VectorCombine] Add constant splat handling for shuffleToIdentity (#92797)

This just adds splat constants, which can be treated like any other
splat which hopefully makes them very simple. It does not try to handle
more complex constant vectors yet, just the more common splats.

Added: 
    

Modified: 
    llvm/lib/Transforms/Vectorize/VectorCombine.cpp
    llvm/test/Transforms/VectorCombine/AArch64/shuffletoidentity.ll

Removed: 
    


################################################################################
diff  --git a/llvm/lib/Transforms/Vectorize/VectorCombine.cpp b/llvm/lib/Transforms/Vectorize/VectorCombine.cpp
index b5a292841172b..03a69d661acde 100644
--- a/llvm/lib/Transforms/Vectorize/VectorCombine.cpp
+++ b/llvm/lib/Transforms/Vectorize/VectorCombine.cpp
@@ -1789,6 +1789,17 @@ bool VectorCombine::foldShuffleToIdentity(Instruction &I) {
       IdentityLeafs.insert(FrontV);
       continue;
     }
+    // Look for constants, for the moment only supporting constant splats.
+    if (auto *C = dyn_cast<Constant>(FrontV);
+        C && C->getSplatValue() &&
+        all_of(drop_begin(Item), [Item](InstLane &IL) {
+          Value *FrontV = Item.front().first;
+          Value *V = IL.first;
+          return !V || V == FrontV;
+        })) {
+      SplatLeafs.insert(FrontV);
+      continue;
+    }
     // Look for a splat value.
     if (all_of(drop_begin(Item), [Item](InstLane &IL) {
           auto [FrontV, FrontLane] = Item.front();

diff  --git a/llvm/test/Transforms/VectorCombine/AArch64/shuffletoidentity.ll b/llvm/test/Transforms/VectorCombine/AArch64/shuffletoidentity.ll
index 7dadeb5d72de0..df42777637ad8 100644
--- a/llvm/test/Transforms/VectorCombine/AArch64/shuffletoidentity.ll
+++ b/llvm/test/Transforms/VectorCombine/AArch64/shuffletoidentity.ll
@@ -281,11 +281,7 @@ define <8 x i8> @undeflane(<8 x i8> %a, <8 x i8> %b) {
 
 define <8 x i8> @constantsplat(<8 x i8> %a) {
 ; CHECK-LABEL: @constantsplat(
-; CHECK-NEXT:    [[AB:%.*]] = shufflevector <8 x i8> [[A:%.*]], <8 x i8> poison, <4 x i32> <i32 3, i32 2, i32 1, i32 0>
-; CHECK-NEXT:    [[AT:%.*]] = shufflevector <8 x i8> [[A]], <8 x i8> poison, <4 x i32> <i32 7, i32 6, i32 5, i32 4>
-; CHECK-NEXT:    [[ABT:%.*]] = add <4 x i8> [[AT]], <i8 10, i8 10, i8 10, i8 10>
-; CHECK-NEXT:    [[ABB:%.*]] = add <4 x i8> [[AB]], <i8 10, i8 10, i8 10, i8 10>
-; CHECK-NEXT:    [[R:%.*]] = shufflevector <4 x i8> [[ABT]], <4 x i8> [[ABB]], <8 x i32> <i32 7, i32 6, i32 5, i32 4, i32 3, i32 2, i32 1, i32 0>
+; CHECK-NEXT:    [[R:%.*]] = add <8 x i8> [[A:%.*]], <i8 10, i8 10, i8 10, i8 10, i8 10, i8 10, i8 10, i8 10>
 ; CHECK-NEXT:    ret <8 x i8> [[R]]
 ;
   %ab = shufflevector <8 x i8> %a, <8 x i8> poison, <4 x i32> <i32 3, i32 2, i32 1, i32 0>
@@ -332,11 +328,7 @@ define <8 x i8> @constant
diff 2(<8 x i8> %a) {
 
 define <8 x half> @constantsplatf(<8 x half> %a) {
 ; CHECK-LABEL: @constantsplatf(
-; CHECK-NEXT:    [[AB:%.*]] = shufflevector <8 x half> [[A:%.*]], <8 x half> poison, <4 x i32> <i32 3, i32 2, i32 1, i32 0>
-; CHECK-NEXT:    [[AT:%.*]] = shufflevector <8 x half> [[A]], <8 x half> poison, <4 x i32> <i32 7, i32 6, i32 5, i32 4>
-; CHECK-NEXT:    [[ABT:%.*]] = fadd <4 x half> [[AT]], <half 0xH4900, half 0xH4900, half 0xH4900, half 0xH4900>
-; CHECK-NEXT:    [[ABB:%.*]] = fadd <4 x half> [[AB]], <half 0xH4900, half 0xH4900, half 0xH4900, half 0xH4900>
-; CHECK-NEXT:    [[R:%.*]] = shufflevector <4 x half> [[ABT]], <4 x half> [[ABB]], <8 x i32> <i32 7, i32 6, i32 5, i32 4, i32 3, i32 2, i32 1, i32 0>
+; CHECK-NEXT:    [[R:%.*]] = fadd <8 x half> [[A:%.*]], <half 0xH4900, half 0xH4900, half 0xH4900, half 0xH4900, half 0xH4900, half 0xH4900, half 0xH4900, half 0xH4900>
 ; CHECK-NEXT:    ret <8 x half> [[R]]
 ;
   %ab = shufflevector <8 x half> %a, <8 x half> poison, <4 x i32> <i32 3, i32 2, i32 1, i32 0>