ARM: fold prologue/epilogue sp updates into push/pop for code size

ARM prologues usually look like:
    push {r7, lr}
    sub sp, sp, #4

If code size is extremely important, this can be optimised to the single
instruction:
    push {r6, r7, lr}

where we don't actually care about the contents of r6, but pushing it subtracts
4 from sp as a side effect.

This should implement such a conversion, predicated on the "minsize" function
attribute (-Oz) since I've yet to find any code it actually makes faster.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@194264 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 126 insertions, 0 deletions

diff --git a/test/CodeGen/ARM/fold-stack-adjust.ll b/test/CodeGen/ARM/fold-stack-adjust.ll
new file mode 100644
index 0000000..c8c48fa
--- /dev/null
+++ b/test/CodeGen/ARM/fold-stack-adjust.ll
@@ -0,0 +1,126 @@
+; RUN: llc -mtriple=thumbv7-apple-darwin-eabi < %s | FileCheck %s
+; RUN: llc -mtriple=thumbv6m-apple-darwin-eabi -disable-fp-elim < %s | FileCheck %s --check-prefix=CHECK-T1
+; RUN: llc -mtriple=thumbv7-apple-darwin-ios -disable-fp-elim < %s | FileCheck %s --check-prefix=CHECK-IOS
+
+
+declare void @bar(i8*)
+
+%bigVec = type [2 x double]
+
+@var = global %bigVec zeroinitializer
+
+define void @check_simple() minsize {
+; CHECK-LABEL: check_simple:
+; CHECK: push.w {r7, r8, r9, r10, r11, lr}
+; CHECK-NOT: sub sp, sp,
+; ...
+; CHECK-NOT: add sp, sp,
+; CHECK: pop.w {r7, r8, r9, r10, r11, pc}
+
+; CHECK-T1-LABEL: check_simple:
+; CHECK-T1: push {r3, r4, r5, r6, r7, lr}
+; CHECK-T1: add r7, sp, #16
+; CHECK-T1-NOT: sub sp, sp,
+; ...
+; CHECK-T1-NOT: add sp, sp,
+; CHECK-T1: pop {r3, r4, r5, r6, r7, pc}
+
+  ; iOS always has a frame pointer and messing with the push affects
+  ; how it's set in the prologue. Make sure we get that right.
+; CHECK-IOS-LABEL: check_simple:
+; CHECK-IOS: push {r3, r4, r5, r6, r7, lr}
+; CHECK-NOT: sub sp,
+; CHECK-IOS: add r7, sp, #16
+; CHECK-NOT: sub sp,
+; ...
+; CHECK-NOT: add sp,
+; CHEC: pop {r3, r4, r5, r6, r7, pc}
+
+  %var = alloca i8, i32 16
+  call void @bar(i8* %var)
+  ret void
+}
+
+define void @check_simple_too_big() minsize {
+; CHECK-LABEL: check_simple_too_big:
+; CHECK: push.w {r11, lr}
+; CHECK: sub sp,
+; ...
+; CHECK: add sp,
+; CHECK: pop.w {r11, pc}
+  %var = alloca i8, i32 64
+  call void @bar(i8* %var)
+  ret void
+}
+
+define void @check_vfp_fold() minsize {
+; CHECK-LABEL: check_vfp_fold:
+; CHECK: push {r[[GLOBREG:[0-9]+]], lr}
+; CHECK: vpush {d6, d7, d8, d9}
+; CHECK-NOT: sub sp,
+; ...
+; CHECK: vldmia r[[GLOBREG]], {d8, d9}
+; ...
+; CHECK-NOT: add sp,
+; CHECK: vpop {d6, d7, d8, d9}
+; CHECKL pop {r[[GLOBREG]], pc}
+
+  ; iOS uses aligned NEON stores here, which is convenient since we
+  ; want to make sure that works too.
+; CHECK-IOS-LABEL: check_vfp_fold:
+; CHECK-IOS: push {r0, r1, r2, r3, r4, r7, lr}
+; CHECK-IOS: sub.w r4, sp, #16
+; CHECK-IOS: bic r4, r4, #15
+; CHECK-IOS: mov sp, r4
+; CHECK-IOS: vst1.64 {d8, d9}, [r4:128]
+; ...
+; CHECK-IOS: add r4, sp, #16
+; CHECK-IOS: vld1.64 {d8, d9}, [r4:128]
+; CHECK-IOS: mov sp, r4
+; CHECK-IOS: pop {r4, r7, pc}
+
+  %var = alloca i8, i32 16
+
+  %tmp = load %bigVec* @var
+  call void @bar(i8* %var)
+  store %bigVec %tmp, %bigVec* @var
+
+  ret void
+}
+
+; This function should use just enough space that the "add sp, sp, ..." could be
+; folded in except that doing so would clobber the value being returned.
+define i64 @check_no_return_clobber() minsize {
+; CHECK-LABEL: check_no_return_clobber:
+; CHECK: push.w {r1, r2, r3, r4, r5, r6, r7, r8, r9, r10, r11, lr}
+; CHECK-NOT: sub sp,
+; ...
+; CHECK: add sp, #40
+; CHECK: pop.w {r11, pc}
+
+  ; Just to keep iOS FileCheck within previous function:
+; CHECK-IOS-LABEL: check_no_return_clobber:
+
+  %var = alloca i8, i32 40
+  call void @bar(i8* %var)
+  ret i64 0
+}
+
+define arm_aapcs_vfpcc double @check_vfp_no_return_clobber() minsize {
+; CHECK-LABEL: check_vfp_no_return_clobber:
+; CHECK: push {r[[GLOBREG:[0-9]+]], lr}
+; CHECK: vpush {d0, d1, d2, d3, d4, d5, d6, d7, d8, d9}
+; CHECK-NOT: sub sp,
+; ...
+; CHECK: add sp, #64
+; CHECK: vpop {d8, d9}
+; CHECK: pop {r[[GLOBREG]], pc}
+
+  %var = alloca i8, i32 64
+
+  %tmp = load %bigVec* @var
+  call void @bar(i8* %var)
+  store %bigVec %tmp, %bigVec* @var
+
+  ret double 1.0
+}