[ARM] Simplify ADJCALLSTACKUP and ADJCALLSTACKDOWN on ARM

A call sequence does not have any unmodeled side effects in of itself.

ADJCALLSTACKUP and ADJCALLSTACKDOWN do, however, so the attribute should be there.

Finally, make ADJCALLSTACKUP and ADJCALLSTACKDOWN codegen only.

Author: AZero13

llvm/lib/Target/ARM/ARMInstrInfo.td

@@ -164,10 +164,9 @@ def ARMWrapperPIC    : SDNode<"ARMISD::WrapperPIC",  SDTIntUnaryOp>;
 def ARMWrapperJT     : SDNode<"ARMISD::WrapperJT",   SDTIntUnaryOp>;
 
 def ARMcallseq_start : SDNode<"ISD::CALLSEQ_START", SDT_ARMCallSeqStart,
-                              [SDNPHasChain, SDNPSideEffect, SDNPOutGlue]>;
+                              [SDNPHasChain, SDNPOutGlue]>;
 def ARMcallseq_end   : SDNode<"ISD::CALLSEQ_END",   SDT_ARMCallSeqEnd,
-                              [SDNPHasChain, SDNPSideEffect,
-                               SDNPOptInGlue, SDNPOutGlue]>;
+                              [SDNPHasChain, SDNPOptInGlue, SDNPOutGlue]>;
 def ARMcopystructbyval : SDNode<"ARMISD::COPY_STRUCT_BYVAL" ,
                                 SDT_ARMStructByVal,
                                 [SDNPHasChain, SDNPInGlue, SDNPOutGlue,
@@ -2203,11 +2202,7 @@ def JUMPTABLE_TBH :
 PseudoInst<(outs), (ins cpinst_operand:$instid, cpinst_operand:$cpidx,
                         i32imm:$size), NoItinerary, []>;
 
-
-// FIXME: Marking these as hasSideEffects is necessary to prevent machine DCE
-// from removing one half of the matched pairs. That breaks PEI, which assumes
-// these will always be in pairs, and asserts if it finds otherwise. Better way?
-let Defs = [SP], Uses = [SP], hasSideEffects = 1 in {
+let Defs = [SP], Uses = [SP], hasSideEffects = 1, isCodeGenOnly = 1 in {
 def ADJCALLSTACKUP :
 PseudoInst<(outs), (ins i32imm:$amt1, i32imm:$amt2, pred:$p), NoItinerary,
            [(ARMcallseq_end timm:$amt1, timm:$amt2)]>;

llvm/lib/Target/ARM/ARMInstrThumb.td

@@ -297,10 +297,7 @@ def non_imm32 : PatLeaf<(i32 GPR), [{ return !isa<ConstantSDNode>(N); }]>;
 //  Miscellaneous Instructions.
 //
 
-// FIXME: Marking these as hasSideEffects is necessary to prevent machine DCE
-// from removing one half of the matched pairs. That breaks PEI, which assumes
-// these will always be in pairs, and asserts if it finds otherwise. Better way?
-let Defs = [SP], Uses = [SP], hasSideEffects = 1 in {
+let Defs = [SP], Uses = [SP], hasSideEffects = 1, isCodeGenOnly = 1 in {
 def tADJCALLSTACKUP :
   PseudoInst<(outs), (ins i32imm:$amt1, i32imm:$amt2), NoItinerary,
              [(ARMcallseq_end imm:$amt1, imm:$amt2)]>,