[llvm] [APInt] remove getClearedMemory and improve slow initialization (PR #106945)

[Princeton Ferro via llvm-commits]

https://github.com/Prince781 updated https://github.com/llvm/llvm-project/pull/106945

>From 4e4deec3fb852be7257911c7a52658f69adec8d2 Mon Sep 17 00:00:00 2001
From: Princeton Ferro <pferro at nvidia.com>
Date: Sun, 1 Sep 2024 22:03:50 -0700
Subject: [PATCH] [APInt] remove getClearedMemory and improve slow
 initialization

---
 llvm/lib/Support/APInt.cpp | 25 ++++++++++---------------
 1 file changed, 10 insertions(+), 15 deletions(-)

diff --git a/llvm/lib/Support/APInt.cpp b/llvm/lib/Support/APInt.cpp
index fe22e9ba04b6f5..b6f8a6abc9304a 100644
--- a/llvm/lib/Support/APInt.cpp
+++ b/llvm/lib/Support/APInt.cpp
@@ -31,14 +31,6 @@ using namespace llvm;
 
 #define DEBUG_TYPE "apint"
 
-/// A utility function for allocating memory, checking for allocation failures,
-/// and ensuring the contents are zeroed.
-inline static uint64_t* getClearedMemory(unsigned numWords) {
-  uint64_t *result = new uint64_t[numWords];
-  memset(result, 0, numWords * sizeof(uint64_t));
-  return result;
-}
-
 /// A utility function for allocating memory and checking for allocation
 /// failure.  The content is not zeroed.
 inline static uint64_t* getMemory(unsigned numWords) {
@@ -74,11 +66,14 @@ inline static unsigned getDigit(char cdigit, uint8_t radix) {
 
 
 void APInt::initSlowCase(uint64_t val, bool isSigned) {
-  U.pVal = getClearedMemory(getNumWords());
-  U.pVal[0] = val;
-  if (isSigned && int64_t(val) < 0)
-    for (unsigned i = 1; i < getNumWords(); ++i)
-      U.pVal[i] = WORDTYPE_MAX;
+  if (isSigned && int64_t(val) < 0) {
+    U.pVal = new WordType[getNumWords()];
+    U.pVal[0] = val;
+    memset(&U.pVal[1], 0xFF, sizeof(WordType) * (getNumWords() - 1));
+  } else {
+    U.pVal = new WordType[getNumWords()]();
+    U.pVal[0] = val;
+  }
   clearUnusedBits();
 }
 
@@ -93,7 +88,7 @@ void APInt::initFromArray(ArrayRef<uint64_t> bigVal) {
     U.VAL = bigVal[0];
   else {
     // Get memory, cleared to 0
-    U.pVal = getClearedMemory(getNumWords());
+    U.pVal = new WordType[getNumWords()]();
     // Calculate the number of words to copy
     unsigned words = std::min<unsigned>(bigVal.size(), getNumWords());
     // Copy the words from bigVal to pVal
@@ -2105,7 +2100,7 @@ void APInt::fromString(unsigned numbits, StringRef str, uint8_t radix) {
   if (isSingleWord())
     U.VAL = 0;
   else
-    U.pVal = getClearedMemory(getNumWords());
+    U.pVal = new WordType[getNumWords()]();
 
   // Figure out if we can shift instead of multiply
   unsigned shift = (radix == 16 ? 4 : radix == 8 ? 3 : radix == 2 ? 1 : 0);