patch for functions with indirect calls and always_inline attribute

[Eric Christopher]

I could be down for this...

Do you have any numbers?

Nits on the patch:

     // Disallow inlining of functions which contain an indirect branch.
-    if (isa<IndirectBrInst>(BI->getTerminator()))
+    if (isa<IndirectBrInst>(BI->getTerminator()) &&
+        !F.hasFnAttribute(Attribute::AlwaysInline))

Update the comment. I'm assuming this can't be hoisted because of the
returns_twice aspect yes?

-define i32 @inner5(i8* %addr) alwaysinline {
+define i32 @inner5(i8* %addr) {

Why the change?

-eric

On Mon, Apr 14, 2014 at 2:49 PM, Gerolf Hoflehner <ghoflehner at apple.com> wrote:
> Hi
>
> llvm currently does not inline functions with indirect branches. We had some
> internal discussion and think the always_inline attribute should overrule
> that restriction.
>
> Gerolf
>
>
>
>
>
> Index: lib/Analysis/IPA/InlineCost.cpp
> ===================================================================
> --- lib/Analysis/IPA/InlineCost.cpp     (revision 206204)
> +++ lib/Analysis/IPA/InlineCost.cpp     (working copy)
> @@ -1301,7 +1301,8 @@
>                                     Attribute::ReturnsTwice);
>    for (Function::iterator BI = F.begin(), BE = F.end(); BI != BE; ++BI) {
>      // Disallow inlining of functions which contain an indirect branch.
> -    if (isa<IndirectBrInst>(BI->getTerminator()))
> +    if (isa<IndirectBrInst>(BI->getTerminator()) &&
> +        !F.hasFnAttribute(Attribute::AlwaysInline))
>        return false;
>
>
>
>      for (BasicBlock::iterator II = BI->begin(), IE = BI->end(); II != IE;
> Index: test/Transforms/Inline/always-inline-attribute.ll
> ===================================================================
> --- test/Transforms/Inline/always-inline-attribute.ll   (revision 0)
> +++ test/Transforms/Inline/always-inline-attribute.ll   (working copy)
> @@ -0,0 +1,26 @@
> +; RUN: opt < %s -O3 -S | FileCheck %s
> + at 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]
> +}
> Index: test/Transforms/Inline/always-inline.ll
> ===================================================================
> --- test/Transforms/Inline/always-inline.ll     (revision 206203)
> +++ test/Transforms/Inline/always-inline.ll     (working copy)
> @@ -78,7 +78,7 @@
>    ret i32 %add
>  }
>
>
>
> -define i32 @inner5(i8* %addr) alwaysinline {
> +define i32 @inner5(i8* %addr) {
>  entry:
>    indirectbr i8* %addr, [ label %one, label %two ]
>
>
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