[PATCH] D11366: Change BlockScanLimit into a command line option.

[Xuetian Weng]

wengxt created this revision.
wengxt added reviewers: jingyue, reames.
wengxt added a subscriber: llvm-commits.

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.

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

http://reviews.llvm.org/D11366

Files:
  lib/Analysis/MemoryDependenceAnalysis.cpp
  test/Analysis/MemoryDependenceAnalysis/memdep-block-scan-limit.ll

Index: test/Analysis/MemoryDependenceAnalysis/memdep-block-scan-limit.ll
===================================================================
--- /dev/null
+++ 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
+}
Index: lib/Analysis/MemoryDependenceAnalysis.cpp
===================================================================
--- lib/Analysis/MemoryDependenceAnalysis.cpp
+++ lib/Analysis/MemoryDependenceAnalysis.cpp
@@ -49,7 +49,11 @@
           "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;


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