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ARM: fix folding of stack-adjustment (yet again).

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When trying to eliminate an "sub sp, sp, #N" instruction by folding
it into an existing push/pop using dummy registers, we need to account
for the fact that this might affect precisely how "fp" gets set in the
prologue.

We were attempting this, but assuming that *whenever* we performed a
fold it would make a difference. This is false, for example, in:
    push {r4, r7, lr}
    add fp, sp, #4
    vpush {d8}
    sub sp, sp, #8

we can fold the "sub" into the "vpush", forming "vpush {d7, d8}".
However, in that case the "add fp" instruction mustn't change, which
we were getting wrong before.

Should fix PR18160.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@196725 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Tim Northover
2013-12-08 15:56:50 +00:00
parent d34102e551
commit 7c4342e90b
2 changed files with 13 additions and 3 deletions
Download Patch File Download Diff File Expand all files Collapse all files

5
lib/Target/ARM/ARMFrameLowering.cpp
View File

@ -256,9 +256,10 @@ void ARMFrameLowering::emitPrologue(MachineFunction &MF) const {
if (NumBytes) { if (NumBytes) {
// Adjust SP after all the callee-save spills. // Adjust SP after all the callee-save spills.
if (tryFoldSPUpdateIntoPushPop(STI, MF, LastPush, NumBytes)) if (tryFoldSPUpdateIntoPushPop(STI, MF, LastPush, NumBytes)) {
if (LastPush == FramePtrPush)
FramePtrOffsetInPush += NumBytes; FramePtrOffsetInPush += NumBytes;
else } else
emitSPUpdate(isARM, MBB, MBBI, dl, TII, -NumBytes, emitSPUpdate(isARM, MBB, MBBI, dl, TII, -NumBytes,
MachineInstr::FrameSetup); MachineInstr::FrameSetup);

9
test/CodeGen/ARM/fold-stack-adjust.ll
View File

@ -137,6 +137,15 @@ define void @test_fold_point(i1 %tst) minsize {
; CHECK: {{LBB[0-9]+_2}}: ; CHECK: {{LBB[0-9]+_2}}:
; CHECK-NEXT: vpop {d7, d8} ; CHECK-NEXT: vpop {d7, d8}
; CHECK-NEXT: pop {r4, pc} ; CHECK-NEXT: pop {r4, pc}
; With a guaranteed frame-pointer, we want to make sure that its offset in the
; push block is correct, even if a few registers have been tacked onto a later
; vpush (PR18160).
; CHECK-IOS-LABEL: test_fold_point:
; CHECK-IOS: push {r4, r7, lr}
; CHECK-IOS-NEXT: add r7, sp, #4
; CHECK-IOS-NEXT: vpush {d7, d8}
; We want some memory so there's a stack adjustment to fold... ; We want some memory so there's a stack adjustment to fold...
%var = alloca i8, i32 8 %var = alloca i8, i32 8