From cd0d0d633bc62f27b4d76ba26d2848577f7c12c4 Mon Sep 17 00:00:00 2001
From: Sanjay Patel <spatel@rotateright.com>
Date: Wed, 13 Apr 2022 06:54:08 -0400
Subject: [PATCH] [SimplifyCFG] make a debug option for case max when
 converting switch to select

This should be "NFC" as written, but it will make D122485 smaller
and give us more flexibility to experiment with optimization level
vs. compile-time.

Differential Revision: https://reviews.llvm.org/D123625
---
 llvm/lib/Transforms/Utils/SimplifyCFG.cpp | 30 +++++++++++++++++-------------
 1 file changed, 17 insertions(+), 13 deletions(-)

diff --git a/llvm/lib/Transforms/Utils/SimplifyCFG.cpp b/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
index c2fa8c6..0b9b590 100644
--- a/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
+++ b/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
@@ -168,6 +168,10 @@ static cl::opt<bool> EnableMergeCompatibleInvokes(
     "simplifycfg-merge-compatible-invokes", cl::Hidden, cl::init(true),
     cl::desc("Allow SimplifyCFG to merge invokes together when appropriate"));
 
+static cl::opt<unsigned> MaxSwitchCasesPerResult(
+    "max-switch-cases-per-result", cl::Hidden, cl::init(2),
+    cl::desc("Limit cases to analyze when converting a switch to select"));
+
 STATISTIC(NumBitMaps, "Number of switch instructions turned into bitmaps");
 STATISTIC(NumLinearMaps,
           "Number of switch instructions turned into linear mapping");
@@ -5602,9 +5606,9 @@ getCaseResults(SwitchInst *SI, ConstantInt *CaseVal, BasicBlock *CaseDest,
 
 // Helper function used to add CaseVal to the list of cases that generate
 // Result. Returns the updated number of cases that generate this result.
-static uintptr_t mapCaseToResult(ConstantInt *CaseVal,
-                                 SwitchCaseResultVectorTy &UniqueResults,
-                                 Constant *Result) {
+static size_t mapCaseToResult(ConstantInt *CaseVal,
+                              SwitchCaseResultVectorTy &UniqueResults,
+                              Constant *Result) {
   for (auto &I : UniqueResults) {
     if (I.first == Result) {
       I.second.push_back(CaseVal);
@@ -5620,12 +5624,13 @@ static uintptr_t mapCaseToResult(ConstantInt *CaseVal,
 // results for the PHI node of the common destination block for a switch
 // instruction. Returns false if multiple PHI nodes have been found or if
 // there is not a common destination block for the switch.
-static bool
-initializeUniqueCases(SwitchInst *SI, PHINode *&PHI, BasicBlock *&CommonDest,
-                      SwitchCaseResultVectorTy &UniqueResults,
-                      Constant *&DefaultResult, const DataLayout &DL,
-                      const TargetTransformInfo &TTI,
-                      uintptr_t MaxUniqueResults, uintptr_t MaxCasesPerResult) {
+static bool initializeUniqueCases(SwitchInst *SI, PHINode *&PHI,
+                                  BasicBlock *&CommonDest,
+                                  SwitchCaseResultVectorTy &UniqueResults,
+                                  Constant *&DefaultResult,
+                                  const DataLayout &DL,
+                                  const TargetTransformInfo &TTI,
+                                  uintptr_t MaxUniqueResults) {
   for (auto &I : SI->cases()) {
     ConstantInt *CaseVal = I.getCaseValue();
 
@@ -5640,11 +5645,11 @@ initializeUniqueCases(SwitchInst *SI, PHINode *&PHI, BasicBlock *&CommonDest,
       return false;
 
     // Add the case->result mapping to UniqueResults.
-    const uintptr_t NumCasesForResult =
+    const size_t NumCasesForResult =
         mapCaseToResult(CaseVal, UniqueResults, Results.begin()->second);
 
     // Early out if there are too many cases for this result.
-    if (NumCasesForResult > MaxCasesPerResult)
+    if (NumCasesForResult > MaxSwitchCasesPerResult)
       return false;
 
     // Early out if there are too many unique results.
@@ -5772,8 +5777,7 @@ static bool trySwitchToSelect(SwitchInst *SI, IRBuilder<> &Builder,
   SwitchCaseResultVectorTy UniqueResults;
   // Collect all the cases that will deliver the same value from the switch.
   if (!initializeUniqueCases(SI, PHI, CommonDest, UniqueResults, DefaultResult,
-                             DL, TTI, /*MaxUniqueResults*/ 2,
-                             /*MaxCasesPerResult*/ 2))
+                             DL, TTI, /*MaxUniqueResults*/ 2))
     return false;
 
   assert(PHI != nullptr && "PHI for value select not found");
-- 
2.7.4