diff options
| author | Dan Gohman <gohman@apple.com> | 2009-11-09 19:29:11 +0000 |
|---|---|---|
| committer | Dan Gohman <gohman@apple.com> | 2009-11-09 19:29:11 +0000 |
| commit | f75ef668a7d35d361e797b7b160008b37d62f15c (patch) | |
| tree | 02bfe2b23f277bcf679ca162bb3472bfaed12382 | |
| parent | 980d494ab6ba3c812194f5cbc14992fa35dcc976 (diff) | |
Default-addressspace null pointers don't alias anything. This allows
GVN to be more aggressive. Patch by Hans Wennborg! (with a comment added by me)
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@86582 91177308-0d34-0410-b5e6-96231b3b80d8
| -rw-r--r-- | lib/Analysis/BasicAliasAnalysis.cpp | 9 | ||||
| -rw-r--r-- | test/Transforms/GVN/null-aliases-nothing.ll | 20 |
2 files changed, 29 insertions, 0 deletions
diff --git a/lib/Analysis/BasicAliasAnalysis.cpp b/lib/Analysis/BasicAliasAnalysis.cpp index 2f4663531a..ea10a83054 100644 --- a/lib/Analysis/BasicAliasAnalysis.cpp +++ b/lib/Analysis/BasicAliasAnalysis.cpp @@ -646,6 +646,15 @@ BasicAliasAnalysis::aliasCheck(const Value *V1, unsigned V1Size, const Value *O1 = V1->getUnderlyingObject(); const Value *O2 = V2->getUnderlyingObject(); + // Null values in the default address space don't point to any object, so they + // don't alias any other pointer. + if (const ConstantPointerNull *CPN = dyn_cast<ConstantPointerNull>(O1)) + if (CPN->getType()->getAddressSpace() == 0) + return NoAlias; + if (const ConstantPointerNull *CPN = dyn_cast<ConstantPointerNull>(O2)) + if (CPN->getType()->getAddressSpace() == 0) + return NoAlias; + if (O1 != O2) { // If V1/V2 point to two different objects we know that we have no alias. if (isIdentifiedObject(O1) && isIdentifiedObject(O2)) diff --git a/test/Transforms/GVN/null-aliases-nothing.ll b/test/Transforms/GVN/null-aliases-nothing.ll new file mode 100644 index 0000000000..bc5c850e5f --- /dev/null +++ b/test/Transforms/GVN/null-aliases-nothing.ll @@ -0,0 +1,20 @@ +; RUN: opt %s -gvn -S | FileCheck %s + +%t = type { i32 } +declare void @test1f(i8*) + +define void @test1(%t* noalias %stuff ) { + %p = getelementptr inbounds %t* %stuff, i32 0, i32 0 + %before = load i32* %p + + call void @test1f(i8* null) + + %after = load i32* %p ; <--- This should be a dead load + %sum = add i32 %before, %after; + + store i32 %sum, i32* %p + ret void +; CHECK: load +; CHECK-NOT: load +; CHECK: ret void +} |