[llvm] [SandboxVectorizer] Define SeedBundle: a set of instructions to be vectorized [retry] (PR #111073)

[Arthur Eubanks via llvm-commits]

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@@ -0,0 +1,65 @@
+//===- SeedCollection.cpp  -0000000----------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/Transforms/Vectorize/SandboxVectorizer/SeedCollector.h"
+#include "llvm/ADT/STLExtras.h"
+#include "llvm/Analysis/LoopAccessAnalysis.h"
+#include "llvm/Analysis/ValueTracking.h"
+#include "llvm/IR/BasicBlock.h"
+#include "llvm/IR/Type.h"
+#include "llvm/SandboxIR/Instruction.h"
+#include "llvm/SandboxIR/Utils.h"
+#include "llvm/Support/Debug.h"
+#include <span>
+
+using namespace llvm;
+namespace llvm::sandboxir {
+
+MutableArrayRef<Instruction *> SeedBundle::getSlice(unsigned StartIdx,
+                                                    unsigned MaxVecRegBits,
+                                                    bool ForcePowerOf2) {
+  // Use uint32_t here for compatibility with IsPowerOf2_32
+
+  // BitCount tracks the size of the working slice. From that we can tell
+  // when the working slice's size is a power-of-two and when it exceeds
+  // the legal size in MaxVecBits.
+  uint32_t BitCount = 0;
+  uint32_t NumElements = 0;
+  // Tracks the most recent slice where NumElements gave a power-of-2 BitCount
+  uint32_t NumElementsPowerOfTwo = 0;
+  uint32_t BitCountPowerOfTwo = 0;
+  // Can't start a slice with a used instruction.
+  assert(!isUsed(StartIdx) && "Expected unused at StartIdx");
+  for (auto S : make_range(Seeds.begin() + StartIdx, Seeds.end())) {
+    uint32_t InstBits = Utils::getNumBits(S);
+    // Stop if this instruction is used, or if adding it puts the slice over
+    // the limit.
+    if (isUsed(StartIdx + NumElements) || BitCount + InstBits > MaxVecRegBits)
+      break;
+    NumElements++;
+    BitCount += InstBits;
+    if (ForcePowerOf2 && isPowerOf2_32(BitCount)) {
+      NumElementsPowerOfTwo = NumElements;
+      BitCountPowerOfTwo = BitCount;
+    }
+  }
+  if (ForcePowerOf2) {
+    NumElements = NumElementsPowerOfTwo;
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aeubanks wrote:

won't this potentially make the slice contain a "used" instruction that we didn't check for? e.g. 0-2 are unused but 3 is used, force power of 2 will make the slice contain 3 which is used

https://github.com/llvm/llvm-project/pull/111073