Teach basicaa to use the nocapture attribute when possible. When the

intrinsics are properly marked nocapture, the fixme should be addressed.

llvm-svn: 61040

2 files changed, 30 insertions, 6 deletions

diff --git a/llvm/lib/Analysis/BasicAliasAnalysis.cpp b/llvm/lib/Analysis/BasicAliasAnalysis.cpp
index 3270f35ac41..57d320971db 100644
--- a/llvm/lib/Analysis/BasicAliasAnalysis.cpp
+++ b/llvm/lib/Analysis/BasicAliasAnalysis.cpp
@@ -63,12 +63,23 @@ static bool AddressMightEscape(const Value *V) {
       // 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/llvm/test/Analysis/BasicAA/nocapture.ll b/llvm/test/Analysis/BasicAA/nocapture.ll
new file mode 100644
index 00000000000..aa4c7f194cd
--- /dev/null
+++ b/llvm/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
+}