[InstCombine] Signed saturation patterns
[llvm-core.git] / include / llvm / Transforms / Scalar / LICM.h
blobf0ea928abd496e0fd20c5091625f3c3165f34696
1 //===- LICM.h - Loop Invariant Code Motion Pass -------*- C++ -*-===//
2 //
3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4 // See https://llvm.org/LICENSE.txt for license information.
5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6 //
7 //===----------------------------------------------------------------------===//
8 //
9 // This pass performs loop invariant code motion, attempting to remove as much
10 // code from the body of a loop as possible. It does this by either hoisting
11 // code into the preheader block, or by sinking code to the exit blocks if it is
12 // safe. This pass also promotes must-aliased memory locations in the loop to
13 // live in registers, thus hoisting and sinking "invariant" loads and stores.
15 // This pass uses alias analysis for two purposes:
17 // 1. Moving loop invariant loads and calls out of loops. If we can determine
18 // that a load or call inside of a loop never aliases anything stored to,
19 // we can hoist it or sink it like any other instruction.
20 // 2. Scalar Promotion of Memory - If there is a store instruction inside of
21 // the loop, we try to move the store to happen AFTER the loop instead of
22 // inside of the loop. This can only happen if a few conditions are true:
23 // A. The pointer stored through is loop invariant
24 // B. There are no stores or loads in the loop which _may_ alias the
25 // pointer. There are no calls in the loop which mod/ref the pointer.
26 // If these conditions are true, we can promote the loads and stores in the
27 // loop of the pointer to use a temporary alloca'd variable. We then use
28 // the SSAUpdater to construct the appropriate SSA form for the value.
30 //===----------------------------------------------------------------------===//
32 #ifndef LLVM_TRANSFORMS_SCALAR_LICM_H
33 #define LLVM_TRANSFORMS_SCALAR_LICM_H
35 #include "llvm/Analysis/LoopInfo.h"
36 #include "llvm/IR/PassManager.h"
37 #include "llvm/Transforms/Scalar/LoopPassManager.h"
39 namespace llvm {
41 extern cl::opt<unsigned> SetLicmMssaOptCap;
42 extern cl::opt<unsigned> SetLicmMssaNoAccForPromotionCap;
44 /// Performs Loop Invariant Code Motion Pass.
45 class LICMPass : public PassInfoMixin<LICMPass> {
46 unsigned LicmMssaOptCap;
47 unsigned LicmMssaNoAccForPromotionCap;
49 public:
50 LICMPass()
51 : LicmMssaOptCap(SetLicmMssaOptCap),
52 LicmMssaNoAccForPromotionCap(SetLicmMssaNoAccForPromotionCap) {}
53 LICMPass(unsigned LicmMssaOptCap, unsigned LicmMssaNoAccForPromotionCap)
54 : LicmMssaOptCap(LicmMssaOptCap),
55 LicmMssaNoAccForPromotionCap(LicmMssaNoAccForPromotionCap) {}
56 PreservedAnalyses run(Loop &L, LoopAnalysisManager &AM,
57 LoopStandardAnalysisResults &AR, LPMUpdater &U);
59 } // end namespace llvm
61 #endif // LLVM_TRANSFORMS_SCALAR_LICM_H