[llvm] [APInt] Simplify APIntOps::avgFloorS etc. NFC. (PR #85212)

[Jay Foad via llvm-commits]

https://github.com/jayfoad created https://github.com/llvm/llvm-project/pull/85212

Removing the extension to FullWidth should make them much more efficient
in the 64-bit case, because 65-bit APInts use a separate allocation for
their bits.


>From ef155e63ca5dc6fe005365c0e283232a7c334838 Mon Sep 17 00:00:00 2001
From: Jay Foad <jay.foad at amd.com>
Date: Thu, 14 Mar 2024 11:47:45 +0000
Subject: [PATCH] [APInt] Simplify APIntOps::avgFloorS etc. NFC.

Removing the extension to FullWidth should make them much more efficient
in the 64-bit case, because 65-bit APInts use a separate allocation for
their bits.
---
 llvm/lib/Support/APInt.cpp | 32 ++++++++------------------------
 1 file changed, 8 insertions(+), 24 deletions(-)

diff --git a/llvm/lib/Support/APInt.cpp b/llvm/lib/Support/APInt.cpp
index 7053f3b87682f8..371d42b221ed62 100644
--- a/llvm/lib/Support/APInt.cpp
+++ b/llvm/lib/Support/APInt.cpp
@@ -3096,37 +3096,21 @@ void llvm::LoadIntFromMemory(APInt &IntVal, const uint8_t *Src,
 }
 
 APInt APIntOps::avgFloorS(const APInt &C1, const APInt &C2) {
-  // Return floor((C1 + C2)/2)
-  assert(C1.getBitWidth() == C2.getBitWidth() && "Unequal bitwidths");
-  unsigned FullWidth = C1.getBitWidth() + 1;
-  APInt C1Ext = C1.sext(FullWidth);
-  APInt C2Ext = C2.sext(FullWidth);
-  return (C1Ext + C2Ext).extractBits(C1.getBitWidth(), 1);
+  // Return floor((C1 + C2) / 2)
+  return (C1 & C2) + (C1 ^ C2).ashr(1);
 }
 
 APInt APIntOps::avgFloorU(const APInt &C1, const APInt &C2) {
-  // Return floor((C1 + C2)/2)
-  assert(C1.getBitWidth() == C2.getBitWidth() && "Unequal bitwidths");
-  unsigned FullWidth = C1.getBitWidth() + 1;
-  APInt C1Ext = C1.zext(FullWidth);
-  APInt C2Ext = C2.zext(FullWidth);
-  return (C1Ext + C2Ext).extractBits(C1.getBitWidth(), 1);
+  // Return floor((C1 + C2) / 2)
+  return (C1 & C2) + (C1 ^ C2).lshr(1);
 }
 
 APInt APIntOps::avgCeilS(const APInt &C1, const APInt &C2) {
-  // Return ceil((C1 + C2)/2)
-  assert(C1.getBitWidth() == C2.getBitWidth() && "Unequal bitwidths");
-  unsigned FullWidth = C1.getBitWidth() + 1;
-  APInt C1Ext = C1.sext(FullWidth);
-  APInt C2Ext = C2.sext(FullWidth);
-  return (C1Ext + C2Ext + 1).extractBits(C1.getBitWidth(), 1);
+  // Return ceil((C1 + C2) / 2)
+  return (C1 | C2) - (C1 ^ C2).ashr(1);
 }
 
 APInt APIntOps::avgCeilU(const APInt &C1, const APInt &C2) {
-  // Return ceil((C1 + C2)/2)
-  assert(C1.getBitWidth() == C2.getBitWidth() && "Unequal bitwidths");
-  unsigned FullWidth = C1.getBitWidth() + 1;
-  APInt C1Ext = C1.zext(FullWidth);
-  APInt C2Ext = C2.zext(FullWidth);
-  return (C1Ext + C2Ext + 1).extractBits(C1.getBitWidth(), 1);
+  // Return ceil((C1 + C2) / 2)
+  return (C1 | C2) - (C1 ^ C2).ashr(1);
 }