[PATCH] D103801: [InstCombine] Support negation of scalable-vector splats

[Fraser Cormack via Phabricator via llvm-commits]

frasercrmck created this revision.
frasercrmck added reviewers: RKSimon, craig.topper, sdesmalen.
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This patch is an extension of D103421 <https://reviews.llvm.org/D103421>. It allows the InstCombiner to
generate the negated form of integer scalable-vector splats. It can
technically handle fixed-length vectors too but those are completely
covered by the preceding logic.

This enables extra combining opportunities for scalable vector types.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D103801

Files:
  llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
  llvm/test/Transforms/InstCombine/sub.ll


Index: llvm/test/Transforms/InstCombine/sub.ll
===================================================================
--- llvm/test/Transforms/InstCombine/sub.ll
+++ llvm/test/Transforms/InstCombine/sub.ll
@@ -839,11 +839,9 @@
   ret <2 x i32> %sub
 }
 
-; FIXME: We're not giving this new 'add' a nsw flag as in the fixed-length case
-; above. We need to be able catch the splat with dyn_castNegVal.
 define <vscale x 2 x i32> @test44scalablevec(<vscale x 2 x i32> %x) {
 ; CHECK-LABEL: @test44scalablevec(
-; CHECK-NEXT:    [[SUB:%.*]] = add <vscale x 2 x i32> [[X:%.*]], shufflevector (<vscale x 2 x i32> insertelement (<vscale x 2 x i32> undef, i32 -32768, i32 0), <vscale x 2 x i32> undef, <vscale x 2 x i32> zeroinitializer)
+; CHECK-NEXT:    [[SUB:%.*]] = add nsw <vscale x 2 x i32> [[X:%.*]], shufflevector (<vscale x 2 x i32> insertelement (<vscale x 2 x i32> undef, i32 -32768, i32 0), <vscale x 2 x i32> undef, <vscale x 2 x i32> zeroinitializer)
 ; CHECK-NEXT:    ret <vscale x 2 x i32> [[SUB]]
 ;
   %sub = sub nsw <vscale x 2 x i32> %x, shufflevector (<vscale x 2 x i32> insertelement (<vscale x 2 x i32> undef, i32 32768, i32 0), <vscale x 2 x i32> undef, <vscale x 2 x i32> zeroinitializer)
Index: llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
===================================================================
--- llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
+++ llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
@@ -924,6 +924,12 @@
     return ConstantExpr::getNeg(CV);
   }
 
+  // Negate integer vector splats.
+  if (auto *CV = dyn_cast<Constant>(V))
+    if (CV->getType()->isVectorTy() &&
+        CV->getType()->getScalarType()->isIntegerTy() && CV->getSplatValue())
+      return ConstantExpr::getNeg(CV);
+
   return nullptr;
 }
 


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