When optimizing for size, don't tail-merge unless it's likely to be a

code-size win, and not when it's only likely to be code-size neutral,
such as when only a single instruction would be eliminated and a new
branch would be required.

This fixes rdar://7392894.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@88692 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 113 insertions, 0 deletions

diff --git a/test/CodeGen/X86/tail-opts.ll b/test/CodeGen/X86/tail-opts.ll
index fdf96d6..0d86e56 100644
--- a/test/CodeGen/X86/tail-opts.ll
+++ b/test/CodeGen/X86/tail-opts.ll
@@ -293,3 +293,116 @@ return:
 }
 
 declare void @func()
+
+; one - One instruction may be tail-duplicated even with optsize.
+
+; CHECK: one:
+; CHECK: movl $0, XYZ(%rip)
+; CHECK: movl $0, XYZ(%rip)
+
+@XYZ = external global i32
+
+define void @one() nounwind optsize {
+entry:
+  %0 = icmp eq i32 undef, 0
+  br i1 %0, label %bbx, label %bby
+
+bby:
+  switch i32 undef, label %bb7 [
+    i32 16, label %return
+  ]
+
+bb7:
+  volatile store i32 0, i32* @XYZ
+  unreachable
+
+bbx:
+  switch i32 undef, label %bb12 [
+    i32 128, label %return
+  ]
+
+bb12:
+  volatile store i32 0, i32* @XYZ
+  unreachable
+
+return:
+  ret void
+}
+
+; two - Same as one, but with two instructions in the common
+; tail instead of one. This is too much to be merged, given
+; the optsize attribute.
+
+; CHECK: two:
+; CHECK-NOT: XYZ
+; CHECK: movl $0, XYZ(%rip)
+; CHECK: movl $1, XYZ(%rip)
+; CHECK-NOT: XYZ
+; CHECK: ret
+
+define void @two() nounwind optsize {
+entry:
+  %0 = icmp eq i32 undef, 0
+  br i1 %0, label %bbx, label %bby
+
+bby:
+  switch i32 undef, label %bb7 [
+    i32 16, label %return
+  ]
+
+bb7:
+  volatile store i32 0, i32* @XYZ
+  volatile store i32 1, i32* @XYZ
+  unreachable
+
+bbx:
+  switch i32 undef, label %bb12 [
+    i32 128, label %return
+  ]
+
+bb12:
+  volatile store i32 0, i32* @XYZ
+  volatile store i32 1, i32* @XYZ
+  unreachable
+
+return:
+  ret void
+}
+
+; two_nosize - Same as two, but without the optsize attribute.
+; Now two instructions are enough to be tail-duplicated.
+
+; CHECK: two_nosize:
+; CHECK: movl $0, XYZ(%rip)
+; CHECK: movl $1, XYZ(%rip)
+; CHECK: movl $0, XYZ(%rip)
+; CHECK: movl $1, XYZ(%rip)
+
+define void @two_nosize() nounwind {
+entry:
+  %0 = icmp eq i32 undef, 0
+  br i1 %0, label %bbx, label %bby
+
+bby:
+  switch i32 undef, label %bb7 [
+    i32 16, label %return
+  ]
+
+bb7:
+  volatile store i32 0, i32* @XYZ
+  volatile store i32 1, i32* @XYZ
+  unreachable
+
+bbx:
+  switch i32 undef, label %bb12 [
+    i32 128, label %return
+  ]
+
+bb12:
+  volatile store i32 0, i32* @XYZ
+  volatile store i32 1, i32* @XYZ
+  unreachable
+
+return:
+  ret void
+}