From bdfefac9a41c2ccd33a440efe1bde099e408225c Mon Sep 17 00:00:00 2001
From: Sanjay Patel <spatel@rotateright.com>
Date: Fri, 7 Oct 2022 11:21:28 -0400
Subject: [PATCH] [InstCombine] refactor sdiv by (negative) power-of-2 folds;
 NFCI

It's probably better to try harder on this kind of
pattern by using ValueTracking.
---
 .../InstCombine/InstCombineMulDivRem.cpp           | 28 +++++++++++-----------
 .../sdiv-exact-by-negative-power-of-two.ll         |  1 +
 .../InstCombine/sdiv-exact-by-power-of-two.ll      |  3 +++
 3 files changed, 18 insertions(+), 14 deletions(-)

diff --git a/llvm/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp b/llvm/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp
index 73afae6..69625c0 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp
@@ -1192,20 +1192,20 @@ Instruction *InstCombinerImpl::visitSDiv(BinaryOperator &I) {
   if (match(Op1, m_SignMask()))
     return new ZExtInst(Builder.CreateICmpEQ(Op0, Op1), Ty);
 
-  // sdiv exact X,  1<<C  -->    ashr exact X, C   iff  1<<C  is non-negative
-  // sdiv exact X, -1<<C  -->  -(ashr exact X, C)
-  if (I.isExact() && ((match(Op1, m_Power2()) && match(Op1, m_NonNegative())) ||
-                      match(Op1, m_NegatedPower2()))) {
-    bool DivisorWasNegative = match(Op1, m_NegatedPower2());
-    if (DivisorWasNegative)
-      Op1 = ConstantExpr::getNeg(cast<Constant>(Op1));
-    auto *AShr = BinaryOperator::CreateExactAShr(
-        Op0, ConstantExpr::getExactLogBase2(cast<Constant>(Op1)), I.getName());
-    if (!DivisorWasNegative)
-      return AShr;
-    Builder.Insert(AShr);
-    AShr->setName(I.getName() + ".neg");
-    return BinaryOperator::CreateNeg(AShr, I.getName());
+  if (I.isExact()) {
+    // sdiv exact X, 1<<C --> ashr exact X, C   iff  1<<C  is non-negative
+    if (match(Op1, m_Power2()) && match(Op1, m_NonNegative())) {
+      Constant *C = ConstantExpr::getExactLogBase2(cast<Constant>(Op1));
+      return BinaryOperator::CreateExactAShr(Op0, C);
+    }
+
+    // sdiv exact X, -1<<C --> -(ashr exact X, C)
+    if (match(Op1, m_NegatedPower2())) {
+      Constant *NegPow2C = ConstantExpr::getNeg(cast<Constant>(Op1));
+      Constant *C = ConstantExpr::getExactLogBase2(NegPow2C);
+      Value *Ashr = Builder.CreateAShr(Op0, C, I.getName() + ".neg", true);
+      return BinaryOperator::CreateNeg(Ashr);
+    }
   }
 
   const APInt *Op1C;
diff --git a/llvm/test/Transforms/InstCombine/sdiv-exact-by-negative-power-of-two.ll b/llvm/test/Transforms/InstCombine/sdiv-exact-by-negative-power-of-two.ll
index ca567c6..e53fd374 100644
--- a/llvm/test/Transforms/InstCombine/sdiv-exact-by-negative-power-of-two.ll
+++ b/llvm/test/Transforms/InstCombine/sdiv-exact-by-negative-power-of-two.ll
@@ -15,6 +15,7 @@ define i8 @t0(i8 %x) {
   %div = sdiv exact i8 %x, -32
   ret i8 %div
 }
+
 define i8 @n1(i8 %x) {
 ; CHECK-LABEL: @n1(
 ; CHECK-NEXT:    [[DIV:%.*]] = sdiv i8 [[X:%.*]], -32
diff --git a/llvm/test/Transforms/InstCombine/sdiv-exact-by-power-of-two.ll b/llvm/test/Transforms/InstCombine/sdiv-exact-by-power-of-two.ll
index 8b41ec0..cb667fe 100644
--- a/llvm/test/Transforms/InstCombine/sdiv-exact-by-power-of-two.ll
+++ b/llvm/test/Transforms/InstCombine/sdiv-exact-by-power-of-two.ll
@@ -15,6 +15,7 @@ define i8 @t0(i8 %x) {
   %div = sdiv exact i8 %x, 32
   ret i8 %div
 }
+
 define i8 @n1(i8 %x) {
 ; CHECK-LABEL: @n1(
 ; CHECK-NEXT:    [[DIV:%.*]] = sdiv i8 [[X:%.*]], 32
@@ -23,6 +24,7 @@ define i8 @n1(i8 %x) {
   %div = sdiv i8 %x, 32 ; not exact
   ret i8 %div
 }
+
 define i8 @n2(i8 %x) {
 ; CHECK-LABEL: @n2(
 ; CHECK-NEXT:    [[TMP1:%.*]] = icmp eq i8 [[X:%.*]], -128
@@ -58,6 +60,7 @@ define <2 x i8> @n5_vec_undef(<2 x i8> %x) {
   %div = sdiv exact <2 x i8> %x, <i8 32, i8 undef>
   ret <2 x i8> %div
 }
+
 define <2 x i8> @n6_vec_negative(<2 x i8> %x) {
 ; CHECK-LABEL: @n6_vec_negative(
 ; CHECK-NEXT:    [[DIV:%.*]] = sdiv exact <2 x i8> [[X:%.*]], <i8 32, i8 -128>
-- 
2.7.4