[MDA] change BlockScanLimit into a command line option.

Summary:
In the benchmark (https://github.com/vetter/shoc) we are researching,
the duplicated load is not eliminated because MemoryDependenceAnalysis
hit the BlockScanLimit. This patch change it into a command line option
instead of a hardcoded value.

Patched by Xuetian Weng.

Test Plan: test/Analysis/MemoryDependenceAnalysis/memdep-block-scan-limit.ll

Reviewers: jingyue, reames

Subscribers: reames, llvm-commits

Differential Revision: http://reviews.llvm.org/D11366

llvm-svn: 242842

diff --git a/llvm/lib/Analysis/MemoryDependenceAnalysis.cpp b/llvm/lib/Analysis/MemoryDependenceAnalysis.cpp
index 782a67b..51e3c4d 100644 (file)
--- a/llvm/lib/Analysis/MemoryDependenceAnalysis.cpp
+++ b/llvm/lib/Analysis/MemoryDependenceAnalysis.cpp
@@ -49,7 +49,11 @@ STATISTIC(NumCacheCompleteNonLocalPtr,
           "Number of block queries that were completely cached");
 
 // Limit for the number of instructions to scan in a block.
-static const unsigned int BlockScanLimit = 100;
+
+static cl::opt<unsigned> BlockScanLimit(
+    "memdep-block-scan-limit", cl::Hidden, cl::init(100),
+    cl::desc("The number of instructions to scan in a block in memory "
+             "dependency analysis (default = 100)"));
 
 // Limit on the number of memdep results to process.
 static const unsigned int NumResultsLimit = 100;

diff --git a/llvm/test/Analysis/MemoryDependenceAnalysis/memdep-block-scan-limit.ll b/llvm/test/Analysis/MemoryDependenceAnalysis/memdep-block-scan-limit.ll
new file mode 100644 (file)
index 0000000..20ca314
--- /dev/null
+++ b/llvm/test/Analysis/MemoryDependenceAnalysis/memdep-block-scan-limit.ll
@@ -0,0 +1,15 @@
+; RUN: opt -S -memdep -gvn -basicaa < %s | FileCheck %s
+; RUN: opt -S -memdep -memdep-block-scan-limit=1 -gvn -basicaa < %s | FileCheck %s --check-prefix=WITH-LIMIT
+; CHECK-LABEL: @test(
+; CHECK: load
+; CHECK-NOT: load
+; WITH-LIMIT-LABEL: @test(
+; WITH-LIMIT-CHECK: load
+; WITH-LIMIT-CHECK: load
+define i32 @test(i32* %p) {
+ %1 = load i32, i32* %p
+ %2 = add i32 %1, 3
+ %3 = load i32, i32* %p
+ %4 = add i32 %2, %3
+ ret i32 %4
+}