[ARM] Fix registers clobbered by SjLj EH on soft-float targets

Currently, the Int_eh_sjlj_dispatchsetup intrinsic is marked as
clobbering all registers, including floating-point registers that may
not be present on the target. This is technically true, as we could get
linked against code that does use the FP registers, but that will not
actually work, as the soft-float code cannot save and restore the FP
registers. SjLj exception handling can only work correctly if either all
or none of the code is built for a target with FP registers. Therefore,
we can assume that, when Int_eh_sjlj_dispatchsetup is compiled for a
soft-float target, it is only going to be linked against other
soft-float code, and so only clobbers the general-purpose registers.
This allows us to check that no non-savable registers are clobbered when
generating the prologue/epilogue.

Differential Revision: https://reviews.llvm.org/D25180

llvm-svn: 283866

llvm/lib/Target/ARM/ARMBaseRegisterInfo.cpp

@@ -131,6 +131,15 @@ ARMBaseRegisterInfo::getTLSCallPreservedMask(const MachineFunction &MF) const {
   return CSR_iOS_TLSCall_RegMask;
 }
 
+const uint32_t *
+ARMBaseRegisterInfo::getSjLjDispatchPreservedMask(const MachineFunction &MF) const {
+  const ARMSubtarget &STI = MF.getSubtarget<ARMSubtarget>();
+  if (!STI.useSoftFloat() && STI.hasVFP2() && !STI.isThumb1Only())
+    return CSR_NoRegs_RegMask;
+  else
+    return CSR_FPRegs_RegMask;
+}
+
 
 const uint32_t *
 ARMBaseRegisterInfo::getThisReturnPreservedMask(const MachineFunction &MF,

llvm/lib/Target/ARM/ARMBaseRegisterInfo.h

@@ -104,6 +104,7 @@ class ARMBaseRegisterInfo : public ARMGenRegisterInfo {
                                        CallingConv::ID) const override;
   const uint32_t *getNoPreservedMask() const override;
   const uint32_t *getTLSCallPreservedMask(const MachineFunction &MF) const;
+  const uint32_t *getSjLjDispatchPreservedMask(const MachineFunction &MF) const;
 
   /// getThisReturnPreservedMask - Returns a call preserved mask specific to the
   /// case that 'returned' is on an i32 first argument if the calling convention

llvm/lib/Target/ARM/ARMCallingConv.td

@@ -242,6 +242,7 @@ def RetCC_ARM_AAPCS_VFP : CallingConv<[
 //===----------------------------------------------------------------------===//
 
 def CSR_NoRegs : CalleeSavedRegs<(add)>;
+def CSR_FPRegs : CalleeSavedRegs<(add (sequence "D%u", 0, 31))>;
 
 def CSR_AAPCS : CalleeSavedRegs<(add LR, R11, R10, R9, R8, R7, R6, R5, R4,
                                      (sequence "D%u", 15, 8))>;

llvm/lib/Target/ARM/ARMISelLowering.cpp

@@ -7865,8 +7865,10 @@ void ARMTargetLowering::EmitSjLjDispatchBlock(MachineInstr &MI,
   const ARMBaseRegisterInfo &RI = AII->getRegisterInfo();
 
   // Add a register mask with no preserved registers.  This results in all
-  // registers being marked as clobbered.
-  MIB.addRegMask(RI.getNoPreservedMask());
+  // registers being marked as clobbered. This can't work if the dispatch block
+  // is in a Thumb1 function and is linked with ARM code which uses the FP
+  // registers, as there is no way to preserve the FP registers in Thumb1 mode.
+  MIB.addRegMask(RI.getSjLjDispatchPreservedMask(*MF));
 
   bool IsPositionIndependent = isPositionIndependent();
   unsigned NumLPads = LPadList.size();

llvm/test/CodeGen/ARM/eh-dispcont.ll

@@ -1,9 +1,9 @@
-; RUN: llc -mtriple armv7-apple-ios -relocation-model=pic -o - %s | FileCheck %s -check-prefix=ARM-PIC
-; RUN: llc -mtriple armv7-apple-ios -relocation-model=static -o - %s | FileCheck %s -check-prefix=ARM-NOPIC
-; RUN: llc -mtriple armv7-apple-ios -relocation-model=dynamic-no-pic -o - %s | FileCheck %s -check-prefix=ARM-NOPIC
-; RUN: llc -mtriple thumbv6-apple-ios -relocation-model=pic -o - %s | FileCheck %s -check-prefix=THUMB1-PIC
-; RUN: llc -mtriple thumbv6-apple-ios -relocation-model=static -o - %s | FileCheck %s -check-prefix=THUMB1-NOPIC
-; RUN: llc -mtriple thumbv6-apple-ios -relocation-model=dynamic-no-pic -o - %s | FileCheck %s -check-prefix=THUMB1-NOPIC
+; RUN: llc -mtriple armv7-apple-ios -relocation-model=pic -o - %s | FileCheck %s -check-prefix=ARM-PIC -check-prefix=ARM
+; RUN: llc -mtriple armv7-apple-ios -relocation-model=static -o - %s | FileCheck %s -check-prefix=ARM-NOPIC -check-prefix=ARM
+; RUN: llc -mtriple armv7-apple-ios -relocation-model=dynamic-no-pic -o - %s | FileCheck %s -check-prefix=ARM-NOPIC -check-prefix=ARM
+; RUN: llc -mtriple thumbv6-apple-ios -relocation-model=pic -o - %s | FileCheck %s -check-prefix=THUMB1-PIC -check-prefix=THUMB1
+; RUN: llc -mtriple thumbv6-apple-ios -relocation-model=static -o - %s | FileCheck %s -check-prefix=THUMB1-NOPIC -check-prefix=THUMB1
+; RUN: llc -mtriple thumbv6-apple-ios -relocation-model=dynamic-no-pic -o - %s | FileCheck %s -check-prefix=THUMB1-NOPIC -check-prefix=THUMB1
 
 @_ZTIi = external constant i8*
 
@@ -41,6 +41,9 @@ attributes #0 = { ssp }
 attributes #1 = { nounwind }
 attributes #2 = { noreturn }
 
+; ARM: vst1.64
+; ARM: vst1.64
+
 ; ARM-PIC: cxa_throw
 ; ARM-PIC: trap
 ; ARM-PIC: adr [[REG1:r[0-9]+]], [[LJTI:.*]]
@@ -63,6 +66,18 @@ attributes #2 = { noreturn }
 ; ARM-NOPIC: .end_data_region
 ; ARM-NOPIC: [[LABEL]]
 
+; ARM: vld1.64
+; ARM: vld1.64
+
+; On Thumb1 targets, we have no way to preserve the floating-point registers.
+; If all other code is built for Thumb1 or is built soft-float, this is not a
+; problem as the FP regs don't need saving. However, if this code is linked
+; against ARM code that uses the FP regs, they won't be restored correctly. We
+; don't support this use-case, but have no way to prevent it in the compiler.
+
+; THUMB1: push {{[^d]*$}}
+; THUMB1-NOT: vst
+
 ; THUMB1-PIC: cxa_throw
 ; THUMB1-PIC: trap
 ; THUMB1-PIC: adr [[REG1:r[0-9]+]], [[LJTI:.*]]
@@ -87,3 +102,6 @@ attributes #2 = { noreturn }
 ; THUMB1-NOPIC: .long [[LABEL:LBB0_[0-9]]]+1
 ; THUMB1-NOPIC: .end_data_region
 ; THUMB1-NOPIC: [[LABEL]]
+
+; THUMB1-NOT: vld
+; THUMB1: pop {{[^d]*$}}