Teach basicaa to use the nocapture attribute when possible. When the
intrinsics are properly marked nocapture, the fixme should be addressed.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@61040 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Analysis/BasicAliasAnalysis.cpp b/lib/Analysis/BasicAliasAnalysis.cpp
index 3270f35..57d3209 100644
--- a/lib/Analysis/BasicAliasAnalysis.cpp
+++ b/lib/Analysis/BasicAliasAnalysis.cpp
@@ -63,12 +63,23 @@
// callees could modify it.
break; // next use
case Instruction::Call:
- // If the call is to a few known safe intrinsics, we know that it does
- // not escape.
- // TODO: Eventually just check the 'nocapture' attribute.
- if (!isa<MemIntrinsic>(I))
- return true;
- break; // next use
+ // If the argument to the call has the nocapture attribute, then the call
+ // may store or load to the pointer, but it cannot escape.
+ if (cast<CallInst>(I)->paramHasAttr(UI.getOperandNo(),
+ Attribute::NoCapture))
+ continue;
+
+ // FIXME: MemIntrinsics should have their operands marked nocapture!
+ if (isa<MemIntrinsic>(I))
+ continue; // next use
+ return true;
+ case Instruction::Invoke:
+ // If the argument to the call has the nocapture attribute, then the call
+ // may store or load to the pointer, but it cannot escape.
+ if (cast<InvokeInst>(I)->paramHasAttr(UI.getOperandNo()-2,
+ Attribute::NoCapture))
+ continue;
+ return true;
default:
return true;
}
diff --git a/test/Analysis/BasicAA/nocapture.ll b/test/Analysis/BasicAA/nocapture.ll
new file mode 100644
index 0000000..aa4c7f1
--- /dev/null
+++ b/test/Analysis/BasicAA/nocapture.ll
@@ -0,0 +1,13 @@
+; RUN: llvm-as < %s | opt -basicaa -gvn -instcombine | llvm-dis | grep {ret i32 0}
+
+declare i32* @test(i32* nocapture)
+
+define i32 @test2() {
+ %P = alloca i32
+ %Q = call i32* @test(i32* %P)
+ %a = load i32* %P
+ store i32 4, i32* %Q ;; cannot clobber P since it is nocapture.
+ %b = load i32* %P
+ %c = sub i32 %a, %b
+ ret i32 %c
+}