2016-10-05 15:39:27 +00:00
|
|
|
; RUN: llc < %s -mtriple=i686-linux -show-mc-encoding | FileCheck %s
|
|
|
|
|
; RUN: llc < %s -mtriple=x86_64-linux -show-mc-encoding | FileCheck %s
|
X86: Fold tail calls into conditional branches where possible (PR26302)
When branching to a block that immediately tail calls, it is possible to fold
the call directly into the branch if the call is direct and there is no stack
adjustment, saving one byte.
Example:
define void @f(i32 %x, i32 %y) {
entry:
%p = icmp eq i32 %x, %y
br i1 %p, label %bb1, label %bb2
bb1:
tail call void @foo()
ret void
bb2:
tail call void @bar()
ret void
}
before:
f:
movl 4(%esp), %eax
cmpl 8(%esp), %eax
jne .LBB0_2
jmp foo
.LBB0_2:
jmp bar
after:
f:
movl 4(%esp), %eax
cmpl 8(%esp), %eax
jne bar
.LBB0_1:
jmp foo
I don't expect any significant size savings from this (on a Clang bootstrap I
saw 288 bytes), but it does make the code a little tighter.
This patch only does 32-bit, but 64-bit would work similarly.
Differential Revision: https://reviews.llvm.org/D24108
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@280832 91177308-0d34-0410-b5e6-96231b3b80d8
2016-09-07 17:52:14 +00:00
|
|
|
|
|
|
|
|
declare void @foo()
|
|
|
|
|
declare void @bar()
|
|
|
|
|
|
|
|
|
|
define void @f(i32 %x, i32 %y) optsize {
|
|
|
|
|
entry:
|
|
|
|
|
%p = icmp eq i32 %x, %y
|
|
|
|
|
br i1 %p, label %bb1, label %bb2
|
|
|
|
|
bb1:
|
|
|
|
|
tail call void @foo()
|
|
|
|
|
ret void
|
|
|
|
|
bb2:
|
|
|
|
|
tail call void @bar()
|
|
|
|
|
ret void
|
|
|
|
|
|
|
|
|
|
; CHECK-LABEL: f:
|
|
|
|
|
; CHECK: cmp
|
|
|
|
|
; CHECK: jne bar
|
|
|
|
|
; Check that the asm doesn't just look good, but uses the correct encoding.
|
|
|
|
|
; CHECK: encoding: [0x75,A]
|
|
|
|
|
; CHECK: jmp foo
|
2016-09-13 00:21:32 +00:00
|
|
|
}
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
declare x86_thiscallcc zeroext i1 @baz(i8*, i32)
|
|
|
|
|
define x86_thiscallcc zeroext i1 @BlockPlacementTest(i8* %this, i32 %x) optsize {
|
|
|
|
|
entry:
|
|
|
|
|
%and = and i32 %x, 42
|
|
|
|
|
%tobool = icmp eq i32 %and, 0
|
|
|
|
|
br i1 %tobool, label %land.end, label %land.rhs
|
|
|
|
|
|
|
|
|
|
land.rhs:
|
|
|
|
|
%and6 = and i32 %x, 44
|
|
|
|
|
%tobool7 = icmp eq i32 %and6, 0
|
|
|
|
|
br i1 %tobool7, label %lor.rhs, label %land.end
|
|
|
|
|
|
|
|
|
|
lor.rhs:
|
|
|
|
|
%call = tail call x86_thiscallcc zeroext i1 @baz(i8* %this, i32 %x) #2
|
|
|
|
|
br label %land.end
|
|
|
|
|
|
|
|
|
|
land.end:
|
|
|
|
|
%0 = phi i1 [ false, %entry ], [ true, %land.rhs ], [ %call, %lor.rhs ]
|
|
|
|
|
ret i1 %0
|
|
|
|
|
|
|
|
|
|
; Make sure machine block placement isn't confused by the conditional tail call,
|
|
|
|
|
; but sees that it can fall through to the next block.
|
|
|
|
|
; CHECK-LABEL: BlockPlacementTest
|
|
|
|
|
; CHECK: je baz
|
|
|
|
|
; CHECK-NOT: xor
|
|
|
|
|
; CHECK: ret
|
|
|
|
|
}
|
