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[LivePhysRegs] Preserve pristine regs in blocks with no successors.
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One common source of blocks with no successors is calls to noreturn
functions; we want to preserve pristine registers in case they throw an
exception.

The whole pristine register thing is messy (we should really prefer to
explicitly model registers), but this fills a hole in the model for now.

Fixes https://bugs.llvm.org/show_bug.cgi?id=36073.

Differential Revision: https://reviews.llvm.org/D42509



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@323559 91177308-0d34-0410-b5e6-96231b3b80d8
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Eli Friedman authored and alexcrichton committed Jan 26, 2018
1 parent 77ab1f0 commit 5c54c25
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Showing 2 changed files with 49 additions and 2 deletions.
4 changes: 2 additions & 2 deletions lib/CodeGen/LivePhysRegs.cpp
Original file line number Diff line number Diff line change
Expand Up @@ -225,10 +225,10 @@ void LivePhysRegs::addLiveOutsNoPristines(const MachineBasicBlock &MBB) {

void LivePhysRegs::addLiveOuts(const MachineBasicBlock &MBB) {
const MachineFunction &MF = *MBB.getParent();
if (!MBB.succ_empty()) {
if (!MBB.isReturnBlock()) {
addPristines(MF);
addLiveOutsNoPristines(MBB);
} else if (MBB.isReturnBlock()) {
} else {
// For the return block: Add all callee saved registers.
const MachineFrameInfo &MFI = MF.getFrameInfo();
if (MFI.isCalleeSavedInfoValid())
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47 changes: 47 additions & 0 deletions test/CodeGen/Thumb/stm-scavenging.ll
Original file line number Diff line number Diff line change
@@ -0,0 +1,47 @@
; RUN: llc < %s | FileCheck %s
target triple = "thumbv6---gnueabi"

; Use STM to save the three registers
; CHECK-LABEL: use_stm:
; CHECK: .save {r7, lr}
; CHECK: .setfp r7, sp
; CHECK: stm r3!, {r0, r1, r2}
; CHECK: bl throws_1
define void @use_stm(i32 %a, i32 %b, i32 %c, i32* %d) local_unnamed_addr noreturn "no-frame-pointer-elim"="true" {
entry:
%arrayidx = getelementptr inbounds i32, i32* %d, i32 2
store i32 %a, i32* %arrayidx, align 4
%arrayidx1 = getelementptr inbounds i32, i32* %d, i32 3
store i32 %b, i32* %arrayidx1, align 4
%arrayidx2 = getelementptr inbounds i32, i32* %d, i32 4
store i32 %c, i32* %arrayidx2, align 4
tail call void @throws_1(i32 %a, i32 %b, i32 %c) noreturn
unreachable
}

; Don't use STM: there is no available register to store
; the address. We could transform this with some extra math, but
; that currently isn't implemented.
; CHECK-LABEL: no_stm:
; CHECK: .save {r7, lr}
; CHECK: .setfp r7, sp
; CHECK: str r0,
; CHECK: str r1,
; CHECK: str r2,
; CHECK: bl throws_2
define void @no_stm(i32 %a, i32 %b, i32 %c, i32* %d) local_unnamed_addr noreturn "no-frame-pointer-elim"="true" {
entry:
%arrayidx = getelementptr inbounds i32, i32* %d, i32 2
store i32 %a, i32* %arrayidx, align 4
%arrayidx1 = getelementptr inbounds i32, i32* %d, i32 3
store i32 %b, i32* %arrayidx1, align 4
%arrayidx2 = getelementptr inbounds i32, i32* %d, i32 4
store i32 %c, i32* %arrayidx2, align 4
tail call void @throws_2(i32 %a, i32 %b, i32 %c, i32* %d) noreturn
unreachable
}


declare void @throws_1(i32, i32, i32) noreturn
declare void @throws_2(i32, i32, i32, i32*) noreturn

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