[llvm] VPlan: simplify mul with zero (PR #127521)

[Ramkumar Ramachandra via llvm-commits]

https://github.com/artagnon created https://github.com/llvm/llvm-project/pull/127521

Extend simplifyRecipe to match mul with zero, and simplify it to zero.

>From 7d12db60725098181e6b3ad765d6fd19998a475c Mon Sep 17 00:00:00 2001
From: Ramkumar Ramachandra <ramkumar.ramachandra at codasip.com>
Date: Mon, 17 Feb 2025 16:48:16 +0000
Subject: [PATCH] VPlan: simplify mul with zero

Extend simplifyRecipe to match mul with zero, and simplify it to zero.
---
 llvm/lib/Transforms/Vectorize/VPlanTransforms.cpp            | 5 +++++
 .../LoopVectorize/RISCV/type-info-cache-evl-crash.ll         | 4 +---
 2 files changed, 6 insertions(+), 3 deletions(-)

diff --git a/llvm/lib/Transforms/Vectorize/VPlanTransforms.cpp b/llvm/lib/Transforms/Vectorize/VPlanTransforms.cpp
index 6c917e4eef655..5ddab73474ba2 100644
--- a/llvm/lib/Transforms/Vectorize/VPlanTransforms.cpp
+++ b/llvm/lib/Transforms/Vectorize/VPlanTransforms.cpp
@@ -951,6 +951,11 @@ static void simplifyRecipe(VPRecipeBase &R, VPTypeAnalysis &TypeInfo) {
   if (match(&R, m_c_Mul(m_VPValue(A), m_SpecificInt(1))))
     return R.getVPSingleValue()->replaceAllUsesWith(A);
 
+  if (match(&R, m_c_Mul(m_VPValue(A), m_SpecificInt(0)))) {
+    unsigned ZeroIdx = R.getOperand(0) == A ? 1 : 0;
+    return R.getVPSingleValue()->replaceAllUsesWith(R.getOperand(ZeroIdx));
+  }
+
   if (match(&R, m_Not(m_Not(m_VPValue(A)))))
     return R.getVPSingleValue()->replaceAllUsesWith(A);
 
diff --git a/llvm/test/Transforms/LoopVectorize/RISCV/type-info-cache-evl-crash.ll b/llvm/test/Transforms/LoopVectorize/RISCV/type-info-cache-evl-crash.ll
index 7de51bc3a8a68..3368d7c44fd5e 100644
--- a/llvm/test/Transforms/LoopVectorize/RISCV/type-info-cache-evl-crash.ll
+++ b/llvm/test/Transforms/LoopVectorize/RISCV/type-info-cache-evl-crash.ll
@@ -45,15 +45,13 @@ define void @type_info_cache_clobber(ptr %dstv, ptr %src, i64 %wide.trip.count)
 ; CHECK-NEXT:    [[TMP14:%.*]] = getelementptr i8, ptr [[TMP13]], i32 0
 ; CHECK-NEXT:    [[VP_OP_LOAD:%.*]] = call <vscale x 8 x i8> @llvm.vp.load.nxv8i8.p0(ptr align 1 [[TMP14]], <vscale x 8 x i1> splat (i1 true), i32 [[TMP11]]), !alias.scope [[META0:![0-9]+]]
 ; CHECK-NEXT:    [[TMP15:%.*]] = call <vscale x 8 x i32> @llvm.vp.zext.nxv8i32.nxv8i8(<vscale x 8 x i8> [[VP_OP_LOAD]], <vscale x 8 x i1> splat (i1 true), i32 [[TMP11]])
-; CHECK-NEXT:    [[VP_OP:%.*]] = call <vscale x 8 x i32> @llvm.vp.mul.nxv8i32(<vscale x 8 x i32> [[TMP15]], <vscale x 8 x i32> zeroinitializer, <vscale x 8 x i1> splat (i1 true), i32 [[TMP11]])
 ; CHECK-NEXT:    [[VP_OP2:%.*]] = call <vscale x 8 x i32> @llvm.vp.ashr.nxv8i32(<vscale x 8 x i32> [[TMP15]], <vscale x 8 x i32> zeroinitializer, <vscale x 8 x i1> splat (i1 true), i32 [[TMP11]])
 ; CHECK-NEXT:    [[VP_OP3:%.*]] = call <vscale x 8 x i32> @llvm.vp.or.nxv8i32(<vscale x 8 x i32> [[VP_OP2]], <vscale x 8 x i32> zeroinitializer, <vscale x 8 x i1> splat (i1 true), i32 [[TMP11]])
 ; CHECK-NEXT:    [[TMP16:%.*]] = icmp ult <vscale x 8 x i32> [[TMP15]], zeroinitializer
 ; CHECK-NEXT:    [[TMP17:%.*]] = call <vscale x 8 x i32> @llvm.vp.select.nxv8i32(<vscale x 8 x i1> [[TMP16]], <vscale x 8 x i32> [[VP_OP3]], <vscale x 8 x i32> zeroinitializer, i32 [[TMP11]])
 ; CHECK-NEXT:    [[TMP18:%.*]] = call <vscale x 8 x i8> @llvm.vp.trunc.nxv8i8.nxv8i32(<vscale x 8 x i32> [[TMP17]], <vscale x 8 x i1> splat (i1 true), i32 [[TMP11]])
 ; CHECK-NEXT:    call void @llvm.vp.scatter.nxv8i8.nxv8p0(<vscale x 8 x i8> [[TMP18]], <vscale x 8 x ptr> align 1 [[BROADCAST_SPLAT]], <vscale x 8 x i1> splat (i1 true), i32 [[TMP11]]), !alias.scope [[META3:![0-9]+]], !noalias [[META0]]
-; CHECK-NEXT:    [[TMP19:%.*]] = call <vscale x 8 x i16> @llvm.vp.trunc.nxv8i16.nxv8i32(<vscale x 8 x i32> [[VP_OP]], <vscale x 8 x i1> splat (i1 true), i32 [[TMP11]])
-; CHECK-NEXT:    call void @llvm.vp.scatter.nxv8i16.nxv8p0(<vscale x 8 x i16> [[TMP19]], <vscale x 8 x ptr> align 2 zeroinitializer, <vscale x 8 x i1> splat (i1 true), i32 [[TMP11]])
+; CHECK-NEXT:    call void @llvm.vp.scatter.nxv8i16.nxv8p0(<vscale x 8 x i16> zeroinitializer, <vscale x 8 x ptr> align 2 zeroinitializer, <vscale x 8 x i1> splat (i1 true), i32 [[TMP11]])
 ; CHECK-NEXT:    [[TMP20:%.*]] = zext i32 [[TMP11]] to i64
 ; CHECK-NEXT:    [[INDEX_EVL_NEXT]] = add i64 [[TMP20]], [[EVL_BASED_IV]]
 ; CHECK-NEXT:    [[INDEX_NEXT]] = add i64 [[INDEX]], [[TMP10]]