[llvm] [instcombine] Delete dead transform for rev(binop splat, rev(x)) (PR #143967)

[Philip Reames via llvm-commits]

https://github.com/preames updated https://github.com/llvm/llvm-project/pull/143967

>From 95d8a50d20ca270e65bb1641b03b6e44b87bcc56 Mon Sep 17 00:00:00 2001
From: Philip Reames <preames at rivosinc.com>
Date: Thu, 12 Jun 2025 13:44:17 -0700
Subject: [PATCH 1/2] [instcombine] Delete dead transform for rev(binop splat,
 rev(x))

We canonicalize splats to RHS, so this transform should be dead code.
---
 llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp | 6 ------
 1 file changed, 6 deletions(-)

diff --git a/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp b/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
index c169ab25b2106..d5738520715b0 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
@@ -3565,12 +3565,6 @@ Instruction *InstCombinerImpl::visitCallInst(CallInst &CI) {
                                              OldBinOp, OldBinOp->getName(),
                                              II->getIterator()));
       }
-      // rev(binop BO0Splat, rev(Y)) --> binop BO0Splat, Y
-      if (match(BO1, m_VecReverse(m_Value(Y))) && isSplatValue(BO0))
-        return replaceInstUsesWith(CI,
-                                   BinaryOperator::CreateWithCopiedFlags(
-                                       OldBinOp->getOpcode(), BO0, Y, OldBinOp,
-                                       OldBinOp->getName(), II->getIterator()));
     }
     // rev(unop rev(X)) --> unop X
     if (match(Vec, m_OneUse(m_UnOp(m_VecReverse(m_Value(X)))))) {

>From f605b39011e117900d72a8009cbb6317e3191c33 Mon Sep 17 00:00:00 2001
From: Philip Reames <preames at rivosinc.com>
Date: Mon, 16 Jun 2025 11:12:08 -0700
Subject: [PATCH 2/2] Remove entire binop case

---
 .../InstCombine/InstCombineCalls.cpp          | 23 ++++---------------
 1 file changed, 5 insertions(+), 18 deletions(-)

diff --git a/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp b/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
index e7fba990f544f..03897117861f6 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
@@ -3555,26 +3555,13 @@ Instruction *InstCombinerImpl::visitCallInst(CallInst &CI) {
     break;
   }
   case Intrinsic::vector_reverse: {
-    Value *BO0, *BO1, *X, *Y;
     Value *Vec = II->getArgOperand(0);
-    if (match(Vec, m_OneUse(m_BinOp(m_Value(BO0), m_Value(BO1))))) {
-      auto *OldBinOp = cast<BinaryOperator>(Vec);
-      if (match(BO0, m_VecReverse(m_Value(X)))) {
-        // rev(binop rev(X), rev(Y)) --> binop X, Y
-        if (match(BO1, m_VecReverse(m_Value(Y))))
-          return replaceInstUsesWith(CI, BinaryOperator::CreateWithCopiedFlags(
-                                             OldBinOp->getOpcode(), X, Y,
-                                             OldBinOp, OldBinOp->getName(),
-                                             II->getIterator()));
-        // rev(binop rev(X), BO1Splat) --> binop X, BO1Splat
-        if (isSplatValue(BO1))
-          return replaceInstUsesWith(CI, BinaryOperator::CreateWithCopiedFlags(
-                                             OldBinOp->getOpcode(), X, BO1,
-                                             OldBinOp, OldBinOp->getName(),
-                                             II->getIterator()));
-      }
-    }
+    // Note: We canonicalize reverse after binops, so we don't need a
+    // corresponding binop case here. TODO: Consider canonicalizing
+    // reverse after fneg?
+
     // rev(unop rev(X)) --> unop X
+    Value *X;
     if (match(Vec, m_OneUse(m_UnOp(m_VecReverse(m_Value(X)))))) {
       auto *OldUnOp = cast<UnaryOperator>(Vec);
       auto *NewUnOp = UnaryOperator::CreateWithCopiedFlags(