Mark that SpeculativeExecution preserves Globals Alias Analysis.

A few benchmarks with lots of accesses to global variables in the hot
loops regressed a lot since r266399, which added the
SpeculativeExecution pass to the default pipeline. The problem is that
this pass doesn't mark Globals Alias Analysis as preserved. Globals
Alias Analysis is computed in a module pass, whereas
SpeculativeExecution is a function pass, and a lot of passes dependent
on the Globals Alias Analysis to optimize these benchmarks are also
function passes. As such, the Globals Alias Analysis information cannot
be recomputed between SpeculativeExecution and the following function
passes needing that information.

SpeculativeExecution doesn't invalidate Globals Alias Analysis, so mark
it as such to fix those performance regressions.

Differential Revision: http://reviews.llvm.org/D19806

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@268370 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/lib/Transforms/Scalar/SpeculativeExecution.cpp b/lib/Transforms/Scalar/SpeculativeExecution.cpp
index 6c210edb2542e6997311dc92f66f832e25501a06..9bf2d62068194f9f49dfce79ae5acdb16226ba86 100644 (file)
--- a/lib/Transforms/Scalar/SpeculativeExecution.cpp
+++ b/lib/Transforms/Scalar/SpeculativeExecution.cpp
@@ -62,6 +62,7 @@
 //===----------------------------------------------------------------------===//
 
 #include "llvm/ADT/SmallSet.h"
+#include "llvm/Analysis/GlobalsModRef.h"
 #include "llvm/Analysis/TargetTransformInfo.h"
 #include "llvm/Analysis/ValueTracking.h"
 #include "llvm/IR/Instructions.h"
@@ -138,6 +139,7 @@ INITIALIZE_PASS_END(SpeculativeExecution, "speculative-execution",
 
 void SpeculativeExecution::getAnalysisUsage(AnalysisUsage &AU) const {
   AU.addRequired<TargetTransformInfoWrapperPass>();
+  AU.addPreserved<GlobalsAAWrapperPass>();
 }
 
 bool SpeculativeExecution::runOnFunction(Function &F) {

diff --git a/test/Transforms/PhaseOrdering/globalaa-retained.ll b/test/Transforms/PhaseOrdering/globalaa-retained.ll
new file mode 100644 (file)
index 0000000..bce193b
--- /dev/null
+++ b/test/Transforms/PhaseOrdering/globalaa-retained.ll
@@ -0,0 +1,26 @@
+; RUN: opt -O3 -S < %s | FileCheck %s
+target datalayout = "e-m:e-i64:64-i128:128-n32:64-S128"
+target triple = "aarch64"
+
+@v = internal unnamed_addr global i32 0, align 4
+@p = common global i32* null, align 8
+
+; Function Attrs: norecurse nounwind
+define void @f(i32 %n) {
+entry:
+  %0 = load i32, i32* @v, align 4
+  %inc = add nsw i32 %0, 1
+  store i32 %inc, i32* @v, align 4
+  %1 = load i32*, i32** @p, align 8
+  store i32 %n, i32* %1, align 4
+  %2 = load i32, i32* @v, align 4
+  %inc1 = add nsw i32 %2, 1
+  store i32 %inc1, i32* @v, align 4
+  ret void
+}
+
+; check variable v is loaded only once after optimization, which should be
+; prove that globalsAA survives until the optimization that can use it to
+; optimize away the duplicate load/stores on variable v.
+; CHECK:     load i32, i32* @v, align 4
+; CHECK-NOT: load i32, i32* @v, align 4