From 03036061c7716f88cef32ebe16f2c10307383ef8 Mon Sep 17 00:00:00 2001
From: Guillaume Chatelet <gchatelet@google.com>
Date: Mon, 20 Jun 2022 09:33:09 +0000
Subject: [PATCH] [Alignment] Use 'previous()' method instead of scalar
 division

This is in preparation of integration with D128052.

Differential Revision: https://reviews.llvm.org/D128169
---
 llvm/include/llvm/Support/Alignment.h           | 15 ++++++++-------
 llvm/lib/CodeGen/GlobalISel/LegalizerHelper.cpp |  4 ++--
 llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp  |  2 +-
 llvm/unittests/Support/AlignmentTest.cpp        |  9 +--------
 4 files changed, 12 insertions(+), 18 deletions(-)

diff --git a/llvm/include/llvm/Support/Alignment.h b/llvm/include/llvm/Support/Alignment.h
index 24a2f62..f12d8ed 100644
--- a/llvm/include/llvm/Support/Alignment.h
+++ b/llvm/include/llvm/Support/Alignment.h
@@ -84,6 +84,14 @@ public:
   /// Needed to interact with C for instance.
   uint64_t value() const { return uint64_t(1) << ShiftValue; }
 
+  // Returns the previous alignment.
+  Align previous() const {
+    assert(ShiftValue != 0 && "Undefined operation");
+    Align Out;
+    Out.ShiftValue = ShiftValue - 1;
+    return Out;
+  }
+
   /// Allow constructions of constexpr Align.
   template <size_t kValue> constexpr static LogValue Constant() {
     return LogValue{static_cast<uint8_t>(CTLog2<kValue>())};
@@ -314,13 +322,6 @@ bool operator>=(MaybeAlign Lhs, MaybeAlign Rhs) = delete;
 bool operator<(MaybeAlign Lhs, MaybeAlign Rhs) = delete;
 bool operator>(MaybeAlign Lhs, MaybeAlign Rhs) = delete;
 
-inline Align operator/(Align Lhs, uint64_t Divisor) {
-  assert(llvm::isPowerOf2_64(Divisor) &&
-         "Divisor must be positive and a power of 2");
-  assert(Lhs != 1 && "Can't halve byte alignment");
-  return Align(Lhs.value() / Divisor);
-}
-
 #ifndef NDEBUG
 // For usage in LLVM_DEBUG macros.
 inline std::string DebugStr(const Align &A) {
diff --git a/llvm/lib/CodeGen/GlobalISel/LegalizerHelper.cpp b/llvm/lib/CodeGen/GlobalISel/LegalizerHelper.cpp
index e8030df..5226816 100644
--- a/llvm/lib/CodeGen/GlobalISel/LegalizerHelper.cpp
+++ b/llvm/lib/CodeGen/GlobalISel/LegalizerHelper.cpp
@@ -7662,7 +7662,7 @@ LegalizerHelper::lowerMemcpy(MachineInstr &MI, Register Dst, Register Src,
     const TargetRegisterInfo *TRI = MF.getSubtarget().getRegisterInfo();
     if (!TRI->hasStackRealignment(MF))
       while (NewAlign > Alignment && DL.exceedsNaturalStackAlignment(NewAlign))
-        NewAlign = NewAlign / 2;
+        NewAlign = NewAlign.previous();
 
     if (NewAlign > Alignment) {
       Alignment = NewAlign;
@@ -7770,7 +7770,7 @@ LegalizerHelper::lowerMemmove(MachineInstr &MI, Register Dst, Register Src,
     const TargetRegisterInfo *TRI = MF.getSubtarget().getRegisterInfo();
     if (!TRI->hasStackRealignment(MF))
       while (NewAlign > Alignment && DL.exceedsNaturalStackAlignment(NewAlign))
-        NewAlign = NewAlign / 2;
+        NewAlign = NewAlign.previous();
 
     if (NewAlign > Alignment) {
       Alignment = NewAlign;
diff --git a/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp b/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
index 3b54916..7a72999 100644
--- a/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
@@ -6751,7 +6751,7 @@ static SDValue getMemcpyLoadsAndStores(SelectionDAG &DAG, const SDLoc &dl,
     const TargetRegisterInfo *TRI = MF.getSubtarget().getRegisterInfo();
     if (!TRI->hasStackRealignment(MF))
       while (NewAlign > Alignment && DL.exceedsNaturalStackAlignment(NewAlign))
-        NewAlign = NewAlign / 2;
+        NewAlign = NewAlign.previous();
 
     if (NewAlign > Alignment) {
       // Give the stack frame object a larger alignment if needed.
diff --git a/llvm/unittests/Support/AlignmentTest.cpp b/llvm/unittests/Support/AlignmentTest.cpp
index 9841e09..f5f0d5e 100644
--- a/llvm/unittests/Support/AlignmentTest.cpp
+++ b/llvm/unittests/Support/AlignmentTest.cpp
@@ -77,7 +77,7 @@ TEST(AlignmentTest, CheckMaybeAlignHasValue) {
 TEST(AlignmentTest, Division) {
   for (uint64_t Value : getValidAlignments()) {
     if (Value > 1) {
-      EXPECT_EQ(Align(Value) / 2, Value / 2);
+      EXPECT_EQ(Align(Value).previous(), Value / 2);
     }
   }
 }
@@ -292,13 +292,6 @@ TEST(AlignmentDeathTest, CantConvertUnsetMaybe) {
   EXPECT_DEATH((MaybeAlign(0).getValue()), ".*");
 }
 
-TEST(AlignmentDeathTest, Division) {
-  EXPECT_DEATH(Align(1) / 2, "Can't halve byte alignment");
-
-  EXPECT_DEATH(Align(8) / 0, "Divisor must be positive and a power of 2");
-  EXPECT_DEATH(Align(8) / 3, "Divisor must be positive and a power of 2");
-}
-
 TEST(AlignmentDeathTest, InvalidCTors) {
   EXPECT_DEATH((Align(0)), "Value must not be 0");
   for (uint64_t Value : getNonPowerOfTwo()) {
-- 
2.7.4