[llvm] [InstCombine] optimize powi(X,Y)/X with Ofast (PR #67236)

[via llvm-commits]

https://github.com/vfdff created https://github.com/llvm/llvm-project/pull/67236

Fixes https://github.com/llvm/llvm-project/pull/67214

>From 96799e402d8d57ffe345bf0600c2e9e15ba54e43 Mon Sep 17 00:00:00 2001
From: zhongyunde 00443407 <zhongyunde at huawei.com>
Date: Sat, 23 Sep 2023 06:40:12 -0400
Subject: [PATCH] [InstCombine] optimize powi(X,Y)/X with Ofast

Fixes https://github.com/llvm/llvm-project/pull/67214
---
 .../Transforms/InstCombine/InstCombineMulDivRem.cpp    | 10 ++++++++++
 llvm/test/Transforms/InstCombine/powi.ll               | 10 ++++++++++
 2 files changed, 20 insertions(+)

diff --git a/llvm/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp b/llvm/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp
index dc091ec7c60e8dd..9c13a63e394a1d5 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp
@@ -1764,6 +1764,16 @@ Instruction *InstCombinerImpl::visitFDiv(BinaryOperator &I) {
     return replaceInstUsesWith(I, Pow);
   }
 
+  if (I.hasAllowReassoc() && I.hasNoInfs() &&
+      match(Op0, m_OneUse(m_Intrinsic<Intrinsic::powi>(m_Specific(Op1),
+                                                       m_Value(Y))))) {
+    Constant *NegOne = ConstantInt::getAllOnesValue(Y->getType());
+    Value *Y1 = Builder.CreateAdd(Y, NegOne);
+    Type *Types[] = {Op1->getType(), Y1->getType()};
+    Value *Pow = Builder.CreateIntrinsic(Intrinsic::powi, Types, {Op1, Y1}, &I);
+    return replaceInstUsesWith(I, Pow);
+  }
+
   return nullptr;
 }
 
diff --git a/llvm/test/Transforms/InstCombine/powi.ll b/llvm/test/Transforms/InstCombine/powi.ll
index 20fe25c50a3ffc0..d58d66660690769 100644
--- a/llvm/test/Transforms/InstCombine/powi.ll
+++ b/llvm/test/Transforms/InstCombine/powi.ll
@@ -258,3 +258,13 @@ define double @different_types_powi(double %x, i32 %y, i64 %z) {
   %mul = fmul reassoc double %p2, %p1
   ret double %mul
 }
+
+define nofpclass(nan inf) double @fdiv_powi(double %x) {
+; CHECK-LABEL: @fdiv_powi(
+; CHECK-NEXT:    [[DIV:%.*]] = fmul fast double [[X:%.*]], [[X]]
+; CHECK-NEXT:    ret double [[DIV]]
+;
+  %p1 = call fast double @llvm.powi.f64.i32(double %x, i32 3)
+  %div = fdiv fast double %p1, %x
+  ret double %div
+}