[LivePhysRegs] Preserve pristine regs in blocks with no successors.

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

Author: Eli Friedman

lib/CodeGen/LivePhysRegs.cpp

@@ -225,10 +225,10 @@ void LivePhysRegs::addLiveOutsNoPristines(const MachineBasicBlock &MBB) {
 
 voidLivePhysRegs::addLiveOuts(const MachineBasicBlock &MBB) {
 const MachineFunction &MF = *MBB.getParent();
-if (!MBB.succ_empty()) {
+if (!MBB.isReturnBlock()) {
 addPristines(MF);
 addLiveOutsNoPristines(MBB);
- } elseif (MBB.isReturnBlock()) {
+ } else {
 // For the return block: Add all callee saved registers.
 const MachineFrameInfo &MFI = MF.getFrameInfo();
 if (MFI.isCalleeSavedInfoValid())

test/CodeGen/Thumb/stm-scavenging.ll

@@ -0,0 +1,47 @@
+; RUN: llc < %s | FileCheck %s
+targettriple = "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
+definevoid@use_stm(i32%a, i32%b, i32%c, i32*%d) local_unnamed_addrnoreturn"no-frame-pointer-elim"="true" {
+entry:
+%arrayidx = getelementptrinboundsi32, i32*%d, i322
+storei32%a, i32*%arrayidx, align4
+%arrayidx1 = getelementptrinboundsi32, i32*%d, i323
+storei32%b, i32*%arrayidx1, align4
+%arrayidx2 = getelementptrinboundsi32, i32*%d, i324
+storei32%c, i32*%arrayidx2, align4
+tailcallvoid@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
+definevoid@no_stm(i32%a, i32%b, i32%c, i32*%d) local_unnamed_addrnoreturn"no-frame-pointer-elim"="true" {
+entry:
+%arrayidx = getelementptrinboundsi32, i32*%d, i322
+storei32%a, i32*%arrayidx, align4
+%arrayidx1 = getelementptrinboundsi32, i32*%d, i323
+storei32%b, i32*%arrayidx1, align4
+%arrayidx2 = getelementptrinboundsi32, i32*%d, i324
+storei32%c, i32*%arrayidx2, align4
+tailcallvoid@throws_2(i32%a, i32%b, i32%c, i32*%d) noreturn
+unreachable
+}
+
+
+declarevoid@throws_1(i32, i32, i32) noreturn
+declarevoid@throws_2(i32, i32, i32, i32*) noreturn
+