[StatepointLowering] Reuse stack slots across basic blocks

During statepoint lowering we can sometimes avoid spilling of the value if we know that it was already spilled for previous statepoint.
We were doing this by checking if incoming statepoint value was lowered into load from stack slot. This was working only in boundaries of one basic block.

But instead of looking at the lowered node we can look directly at the llvm-ir value and if it was gc.relocate (or some simple modification of it) look up stack slot for it's derived pointer and reuse stack slot from it. This allows us to look across basic block boundaries.

Differential Revision: http://reviews.llvm.org/D10251

llvm-svn: 239472

1 files changed, 45 insertions, 1 deletions

diff --git a/llvm/test/CodeGen/X86/statepoint-stack-usage.ll b/llvm/test/CodeGen/X86/statepoint-stack-usage.ll
index 02d20c9fcb9..2299d724636 100644
--- a/llvm/test/CodeGen/X86/statepoint-stack-usage.ll
+++ b/llvm/test/CodeGen/X86/statepoint-stack-usage.ll
@@ -52,9 +52,53 @@ define i32 @reserve_first(i32 addrspace(1)* %a, i32 addrspace(1)* %b, i32 addrsp
   ret i32 1
 }
 
+; Test that stack slots are reused for invokes
+define i32 @back_to_back_invokes(i32 addrspace(1)* %a, i32 addrspace(1)* %b, i32 addrspace(1)* %c) #1 gc "statepoint-example" {
+; CHECK-LABEL: back_to_back_invokes
+entry:
+  ; The exact stores don't matter, but there need to be three stack slots created
+  ; CHECK: movq	%rdi, 16(%rsp)
+  ; CHECK: movq	%rdx, 8(%rsp)
+  ; CHECK: movq	%rsi, (%rsp)
+  ; CHECK: callq
+  %safepoint_token = invoke i32 (i64, i32, void ()*, i32, i32, ...) @llvm.experimental.gc.statepoint.p0f_isVoidf(i64 0, i32 0, void ()* undef, i32 0, i32 0, i32 0, i32 5, i32 0, i32 -1, i32 0, i32 0, i32 0, i32 addrspace(1)* %a, i32 addrspace(1)* %b, i32 addrspace(1)* %c)
+                   to label %normal_return unwind label %exceptional_return
+
+normal_return:
+  %a1 = tail call coldcc i32 addrspace(1)* @llvm.experimental.gc.relocate.p1i32(i32 %safepoint_token, i32 12, i32 12)
+  %b1 = tail call coldcc i32 addrspace(1)* @llvm.experimental.gc.relocate.p1i32(i32 %safepoint_token, i32 12, i32 13)
+  %c1 = tail call coldcc i32 addrspace(1)* @llvm.experimental.gc.relocate.p1i32(i32 %safepoint_token, i32 12, i32 14)
+  ; Should work even through bitcasts
+  %c1.casted = bitcast i32 addrspace(1)* %c1 to i8 addrspace(1)*
+  ; This is the key check.  There should NOT be any memory moves here
+  ; CHECK-NOT: movq
+  ; CHECK: callq
+  %safepoint_token2 = invoke i32 (i64, i32, void ()*, i32, i32, ...) @llvm.experimental.gc.statepoint.p0f_isVoidf(i64 0, i32 0, void ()* undef, i32 0, i32 0, i32 0, i32 5, i32 0, i32 -1, i32 0, i32 0, i32 0, i8 addrspace(1)* %c1.casted, i32 addrspace(1)* %b1, i32 addrspace(1)* %a1)
+                    to label %normal_return2 unwind label %exceptional_return2
+
+normal_return2:
+  %a2 = tail call coldcc i32 addrspace(1)* @llvm.experimental.gc.relocate.p1i32(i32 %safepoint_token2, i32 12, i32 14)
+  %b2 = tail call coldcc i32 addrspace(1)* @llvm.experimental.gc.relocate.p1i32(i32 %safepoint_token2, i32 12, i32 13)
+  %c2 = tail call coldcc i8 addrspace(1)* @llvm.experimental.gc.relocate.p1i8(i32 %safepoint_token2, i32 12, i32 12)
+  ret i32 1
+
+exceptional_return:
+  %landing_pad = landingpad { i8*, i32 } personality i32 ()* @"personality_function"
+          cleanup
+  ret i32 0
+
+exceptional_return2:
+  %landing_pad2 = landingpad { i8*, i32 } personality i32 ()* @"personality_function"
+          cleanup
+  ret i32 0
+}
+
 ; Function Attrs: nounwind
 declare i32 addrspace(1)* @llvm.experimental.gc.relocate.p1i32(i32, i32, i32) #3
+declare i8 addrspace(1)* @llvm.experimental.gc.relocate.p1i8(i32, i32, i32) #3
 
 declare i32 @llvm.experimental.gc.statepoint.p0f_isVoidf(i64, i32, void ()*, i32, i32, ...)
 
-attributes #1 = { uwtable }
\ No newline at end of file
+declare i32 @"personality_function"()
+
+attributes #1 = { uwtable }