[llvm-branch-commits] [llvm] 44efac1 - Revert "[VPlan] Replace first-lane uses of BuildVector. (#206566)"

[via llvm-branch-commits]

Author: Aiden Grossman
Date: 2026-06-30T10:00:56-07:00
New Revision: 44efac15bbf786023afe35dd894fcf4e820291be

URL: https://github.com/llvm/llvm-project/commit/44efac15bbf786023afe35dd894fcf4e820291be
DIFF: https://github.com/llvm/llvm-project/commit/44efac15bbf786023afe35dd894fcf4e820291be.diff

LOG: Revert "[VPlan] Replace first-lane uses of BuildVector. (#206566)"

This reverts commit f15288c2af25d0aca6516ca0b9a09d0ca90f5888.

Added: 
    

Modified: 
    llvm/lib/Transforms/Vectorize/VPlanTransforms.cpp
    llvm/test/Transforms/LoopVectorize/VPlan/buildvector-first-lane-only.ll

Removed: 
    


################################################################################
diff  --git a/llvm/lib/Transforms/Vectorize/VPlanTransforms.cpp b/llvm/lib/Transforms/Vectorize/VPlanTransforms.cpp
index 5834f38e96b84..ceb7c38ca3e29 100644
--- a/llvm/lib/Transforms/Vectorize/VPlanTransforms.cpp
+++ b/llvm/lib/Transforms/Vectorize/VPlanTransforms.cpp
@@ -1736,14 +1736,6 @@ static void simplifyRecipe(VPSingleDefRecipe *Def) {
     return;
   }
 
-  // Replace uses of a BuildVector by users that only use its first lane with
-  // its first operand directly.
-  if (match(Def, m_BuildVector())) {
-    Def->replaceUsesWithIf(Def->getOperand(0), [Def](VPUser &U, unsigned) {
-      return U.usesFirstLaneOnly(Def);
-    });
-  }
-
   // Look through broadcast of single-scalar when used as select conditions; in
   // that case the scalar condition can be used directly.
   if (match(Def,

diff  --git a/llvm/test/Transforms/LoopVectorize/VPlan/buildvector-first-lane-only.ll b/llvm/test/Transforms/LoopVectorize/VPlan/buildvector-first-lane-only.ll
index 8361c2d3a59b2..54614ad7c2035 100644
--- a/llvm/test/Transforms/LoopVectorize/VPlan/buildvector-first-lane-only.ll
+++ b/llvm/test/Transforms/LoopVectorize/VPlan/buildvector-first-lane-only.ll
@@ -19,15 +19,19 @@ define i32 @last_active_lane_live_out(i32 %x) {
 ; CHECK-NEXT:  Successor(s): middle.block
 ; CHECK-EMPTY:
 ; CHECK-NEXT:  middle.block:
-; CHECK-NEXT:    EMIT vp<%active.lane.mask> = active lane mask ir<0>, ir<2>, ir<1>
-; CHECK-NEXT:    EMIT vp<[[VP5:%[0-9]+]]> = not vp<%active.lane.mask>
-; CHECK-NEXT:    EMIT vp<%first.inactive.lane> = first-active-lane vp<[[VP5]]>
+; CHECK-NEXT:    vp<[[VP5:%[0-9]+]]> = SCALAR-STEPS ir<0>, ir<1>, ir<4>, ir<1>
+; CHECK-NEXT:    vp<[[VP6:%[0-9]+]]> = SCALAR-STEPS ir<0>, ir<1>, ir<4>, ir<2>
+; CHECK-NEXT:    vp<[[VP7:%[0-9]+]]> = SCALAR-STEPS ir<0>, ir<1>, ir<4>, ir<3>
+; CHECK-NEXT:    EMIT vp<[[VP8:%[0-9]+]]> = buildvector ir<0>, vp<[[VP5]]>, vp<[[VP6]]>, vp<[[VP7]]>
+; CHECK-NEXT:    EMIT vp<%active.lane.mask> = active lane mask vp<[[VP8]]>, ir<2>, ir<1>
+; CHECK-NEXT:    EMIT vp<[[VP9:%[0-9]+]]> = not vp<%active.lane.mask>
+; CHECK-NEXT:    EMIT vp<%first.inactive.lane> = first-active-lane vp<[[VP9]]>
 ; CHECK-NEXT:    EMIT vp<%last.active.lane> = sub vp<%first.inactive.lane>, ir<1>
-; CHECK-NEXT:    EMIT vp<[[VP6:%[0-9]+]]> = extractelement vp<[[VP4]]>, vp<%last.active.lane>
+; CHECK-NEXT:    EMIT vp<[[VP10:%[0-9]+]]> = extractelement vp<[[VP4]]>, vp<%last.active.lane>
 ; CHECK-NEXT:  Successor(s): ir-bb<exit>
 ; CHECK-EMPTY:
 ; CHECK-NEXT:  ir-bb<exit>:
-; CHECK-NEXT:    IR   %red.lcssa = phi i32 [ %red, %loop ] (extra operand: vp<[[VP6]]> from middle.block)
+; CHECK-NEXT:    IR   %red.lcssa = phi i32 [ %red, %loop ] (extra operand: vp<[[VP10]]> from middle.block)
 ; CHECK-NEXT:  No successors
 ; CHECK-NEXT:  }
 ;