Introduce -enable-global-analyses to allow users to disable inter-procedural analyses

[nlopes]

Summary

Alive2 doesn't support verification of optimizations that use inter-procedural analyses.
Right now, clang uses GlobalsAA by default and there's no way to disable it. This leads to Alive2 producing false positives.

Example:

file.c:

static int x;
int f() {
  x = 0;
  *p = 1;
  x = 2;
  return *p;
}

This file.c right now compiles to:

define i32 @f(ptr nocapture noundef %p) {
  store i32 1, ptr %p, align 4
  store i1 true, ptr @x, align 4
  ret i32 1
}

without globalsaa:
$ clang -S -emit-llvm -o - -O3 file.c -mllvm -enable-global-analyses=0

define i32 @f(ptr nocapture noundef %p) {
  store i32 1, ptr %p, align 4
  store i1 true, ptr @x, align 4
  %0 = load i32, ptr %p, align 4
  ret i32 %0
}

[nikic]

LGTM

llvm/lib/Passes/PassBuilderPipelines.cpp

189

Make the var name EnableGlobalAnalyses to match the option name?

[fhahn]

Could you also add a test for the option?

[nlopes]

In D134139#3799277, @fhahn wrote:

Could you also add a test for the option?

Sure: https://github.com/llvm/llvm-project/commit/bc698c77af64acfd4f0fa13263d8f708f2f116df

llvm/lib/Passes/PassBuilderPipelines.cpp

 static cl::opt<bool> EnableMergeFunctions(
     "enable-merge-functions", cl::init(false), cl::Hidden,
     cl::desc("Enable function merging as part of the optimization pipeline"));
 
 static cl::opt<bool> EnablePostPGOLoopRotation(
     "enable-post-pgo-loop-rotation", cl::init(true), cl::Hidden,
     cl::desc("Run the loop rotation transformation after PGO instrumentation"));
 
+static cl::opt<bool> EnableGlobalAnalysis(
+    "enable-global-analyses", cl::init(true), cl::Hidden,
+    cl::desc("Enable inter-procedural analyses"));
+
 PipelineTuningOptions::PipelineTuningOptions() {
   LoopInterleaving = true;
   LoopVectorization = true;
   SLPVectorization = false;
   LoopUnrolling = true;
   ForgetAllSCEVInLoopUnroll = ForgetSCEVInLoopUnroll;
   LicmMssaOptCap = SetLicmMssaOptCap;
   LicmMssaNoAccForPromotionCap = SetLicmMssaNoAccForPromotionCap;
AAManager PassBuilder::buildDefaultAAPipeline() {
   // information about aliasing.
   AA.registerFunctionAnalysis<ScopedNoAliasAA>();
   AA.registerFunctionAnalysis<TypeBasedAA>();
 
   // Add support for querying global aliasing information when available.
   // Because the `AAManager` is a function analysis and `GlobalsAA` is a module
   // analysis, all that the `AAManager` can do is query for any *cached*
   // results from `GlobalsAA` through a readonly proxy.
+  if (EnableGlobalAnalysis)
     AA.registerModuleAnalysis<GlobalsAA>();
 
   // Add target-specific alias analyses.
   if (TM)
     TM->registerDefaultAliasAnalyses(AA);
 
   return AA;
 }