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[ARM] Fix PR35481

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This patch allows `r7` to be used, regardless of its use as a frame pointer, as
a temporary register when popping `lr`, and also falls back to using a high
temporary register if, for some reason, we weren't able to find a suitable low
one.

Differential revision: https://reviews.llvm.org/D40961
Fixes https://bugs.llvm.org/show_bug.cgi?id=35481

llvm-svn: 321989
This commit is contained in:
Momchil Velikov 2018-01-08 11:32:37 +00:00
parent c60fcd822b
commit c0e2b430f9
2 changed files with 38 additions and 5 deletions
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17
lib/Target/ARM/Thumb1FrameLowering.cpp
View File

@ -611,6 +611,12 @@ bool Thumb1FrameLowering::emitPopSpecialFixUp(MachineBasicBlock &MBB,
unsigned TemporaryReg = 0; unsigned TemporaryReg = 0;
BitVector PopFriendly = BitVector PopFriendly =
TRI.getAllocatableSet(MF, TRI.getRegClass(ARM::tGPRRegClassID)); TRI.getAllocatableSet(MF, TRI.getRegClass(ARM::tGPRRegClassID));
// R7 may be used as a frame pointer, hence marked as not generally
// allocatable, however there's no reason to not use it as a temporary for
// restoring LR.
if (STI.useR7AsFramePointer())
PopFriendly.set(ARM::R7);
assert(PopFriendly.any() && "No allocatable pop-friendly register?!"); assert(PopFriendly.any() && "No allocatable pop-friendly register?!");
// Rebuild the GPRs from the high registers because they are removed // Rebuild the GPRs from the high registers because they are removed
// form the GPR reg class for thumb1. // form the GPR reg class for thumb1.
@ -622,19 +628,22 @@ bool Thumb1FrameLowering::emitPopSpecialFixUp(MachineBasicBlock &MBB,
GPRsNoLRSP.reset(ARM::PC); GPRsNoLRSP.reset(ARM::PC);
findTemporariesForLR(GPRsNoLRSP, PopFriendly, UsedRegs, PopReg, TemporaryReg); findTemporariesForLR(GPRsNoLRSP, PopFriendly, UsedRegs, PopReg, TemporaryReg);
// If we couldn't find a pop-friendly register, restore LR before popping the // If we couldn't find a pop-friendly register, try restoring LR before
// other callee-saved registers, so we can use one of them as a temporary. // popping the other callee-saved registers, so we could use one of them as a
// temporary.
bool UseLDRSP = false; bool UseLDRSP = false;
if (!PopReg && MBBI != MBB.begin()) { if (!PopReg && MBBI != MBB.begin()) {
auto PrevMBBI = MBBI; auto PrevMBBI = MBBI;
PrevMBBI--; PrevMBBI--;
if (PrevMBBI->getOpcode() == ARM::tPOP) { if (PrevMBBI->getOpcode() == ARM::tPOP) {
MBBI = PrevMBBI; UsedRegs.stepBackward(*PrevMBBI);
UsedRegs.stepBackward(*MBBI);
findTemporariesForLR(GPRsNoLRSP, PopFriendly, UsedRegs, PopReg, TemporaryReg); findTemporariesForLR(GPRsNoLRSP, PopFriendly, UsedRegs, PopReg, TemporaryReg);
if (PopReg) {
MBBI = PrevMBBI;
UseLDRSP = true; UseLDRSP = true;
} }
} }
}
if (!DoIt && !PopReg && !TemporaryReg) if (!DoIt && !PopReg && !TemporaryReg)
return false; return false;

24
test/CodeGen/Thumb/PR35481.ll Normal file
View File

@ -0,0 +1,24 @@
; RUN: llc -mtriple thumbv4t-eabi < %s | FileCheck %s --check-prefix=CHECK --check-prefix=CHECK-V4T
; RUN: llc -mtriple armv8m.base-eabi < %s | FileCheck %s --check-prefix=CHECK --check-prefix=CHECK-V8M
target datalayout = "e-m:e-p:32:32-i64:64-v128:64:128-a:0:32-n32-S64"
; Function Attrs: nounwind
define <4 x i32> @f() local_unnamed_addr #0 {
entry:
%call = tail call i32 @h(i32 1)
%call1 = tail call <4 x i32> @g(i32 %call, i32 2, i32 3, i32 4)
ret <4 x i32> %call1
; CHECK: ldr r7, [sp, #4]
; CHECK-NEXT: mov lr, r7
; CHECK-NEXT: pop {r7}
; CHECK-NEXT: add sp, #4
; CHECK-V47: bx lr
; CHECK-V8M: b g
}
declare <4 x i32> @g(i32, i32, i32, i32) local_unnamed_addr
declare i32 @h(i32) local_unnamed_addr
attributes #0 = { "disable-tail-calls"="false" "no-frame-pointer-elim"="true" "no-frame-pointer-elim-non-leaf" }