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 3270f35ac411d9cf7b3f25668d196b69a99c6f8d..57d320971dbef17b0b9e3dba382f67bc4cb825c4 100644 (file)
--- a/lib/Analysis/BasicAliasAnalysis.cpp
+++ b/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/test/Analysis/BasicAA/nocapture.ll b/test/Analysis/BasicAA/nocapture.ll
new file mode 100644 (file)
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
+}