Inline a function when the always_inline attribute

is set even when it contains a indirect branch.
The attribute overrules correctness concerns
like the escape of a local block address.

This is for rdar://16501761

llvm-svn: 206429

llvm/lib/Analysis/IPA/InlineCost.cpp

@@ -1300,8 +1300,14 @@ bool InlineCostAnalysis::isInlineViable(Function &F) {
     F.getAttributes().hasAttribute(AttributeSet::FunctionIndex,
                                    Attribute::ReturnsTwice);
   for (Function::iterator BI = F.begin(), BE = F.end(); BI != BE; ++BI) {
-    // Disallow inlining of functions which contain an indirect branch.
+    // Disallow inlining of functions which contain an indirect branch,
-    if (isa<IndirectBrInst>(BI->getTerminator()))
+    // unless the always_inline attribute is set.
+    // The attribute serves as a assertion that no local address
+    // like a block label can escpape the function.
+    // Revisit enabling inlining for functions with indirect branches
+    // when a more sophisticated espape/points-to analysis becomes available.
+    if (isa<IndirectBrInst>(BI->getTerminator()) &&
+        !F.hasFnAttribute(Attribute::AlwaysInline))
       return false;
 
     for (BasicBlock::iterator II = BI->begin(), IE = BI->end(); II != IE;

llvm/test/Transforms/Inline/always-inline-attribute.ll

@@ -0,0 +1,26 @@
+; RUN: opt < %s -O3 -S | FileCheck %s
+@gv = external global i32
+
+define i32 @main() nounwind {
+; CHECK-NOT: call i32 @foo
+  %1 = load i32* @gv, align 4
+  %2 = tail call i32 @foo(i32 %1)
+  unreachable
+}
+
+define internal i32 @foo(i32) alwaysinline {
+  br label %2
+
+; <label>:2                                       ; preds = %8, %1
+  %3 = phi i32 [ %0, %1 ], [ %10, %8 ]
+  %4 = phi i8* [ blockaddress(@foo, %2), %1 ], [ %6, %8 ]
+  %5 = icmp eq i32 %3, 1
+  %6 = select i1 %5, i8* blockaddress(@foo, %8), i8* %4
+  %7 = add nsw i32 %3, -1
+  br label %8
+
+; <label>:8                                       ; preds = %8, %2
+  %9 = phi i32 [ %7, %2 ], [ %10, %8 ]
+  %10 = add nsw i32 %9, -1
+  indirectbr i8* %6, [label %2, label %8]
+}

llvm/test/Transforms/Inline/always-inline.ll

@@ -78,7 +78,7 @@ entry:
   ret i32 %add
 }
 
-define i32 @inner5(i8* %addr) alwaysinline {
+define i32 @inner5(i8* %addr) {
 entry:
   indirectbr i8* %addr, [ label %one, label %two ]