[MSP430] Fix PR32769: Select8 and Select16 need to have SR in Uses.

[pftbest]

Summary

If Select pseudo instruction doesn't have use SR, then
CMP instructions are being marked as dead and later can be
removed by MachineCSE pass. This leads to incorrect code
generation.

[efriedma]

Looks fine, but someone who knows the MSP430 backend better should look at this.

lib/Target/MSP430/MSP430InstrInfo.td

125

Not sure this comment adds anything.

[asl]

In general, LGTM. I agree with Eli about irrelevance of comment.

[pftbest]

Removed the comment.

lib/Target/MSP430/MSP430InstrInfo.td

def ADJCALLSTACKDOWN : Pseudo<(outs), (ins i16imm:$amt),
                               "#ADJCALLSTACKDOWN",
                               [(MSP430callseq_start timm:$amt)]>;
 def ADJCALLSTACKUP   : Pseudo<(outs), (ins i16imm:$amt1, i16imm:$amt2),
                               "#ADJCALLSTACKUP",
                               [(MSP430callseq_end timm:$amt1, timm:$amt2)]>;
 }
 
 let usesCustomInserter = 1 in {
+  // SR is marked as used to prevent CMPs from appearing dead.
+  let Uses = [SR] in {
   def Select8  : Pseudo<(outs GR8:$dst), (ins GR8:$src, GR8:$src2, i8imm:$cc),
                         "# Select8 PSEUDO",
                         [(set GR8:$dst,
                           (MSP430selectcc GR8:$src, GR8:$src2, imm:$cc))]>;
   def Select16 : Pseudo<(outs GR16:$dst), (ins GR16:$src, GR16:$src2, i8imm:$cc),
                         "# Select16 PSEUDO",
                         [(set GR16:$dst,
                           (MSP430selectcc GR16:$src, GR16:$src2, imm:$cc))]>;
+  }
   let Defs = [SR] in {
   def Shl8     : Pseudo<(outs GR8:$dst), (ins GR8:$src, GR8:$cnt),
                         "# Shl8 PSEUDO",
                         [(set GR8:$dst, (MSP430shl GR8:$src, GR8:$cnt))]>;
   def Shl16    : Pseudo<(outs GR16:$dst), (ins GR16:$src, GR8:$cnt),
                         "# Shl16 PSEUDO",
                         [(set GR16:$dst, (MSP430shl GR16:$src, GR8:$cnt))]>;
   def Sra8     : Pseudo<(outs GR8:$dst), (ins GR8:$src, GR8:$cnt),

test/CodeGen/MSP430/select-use-sr.ll

+; RUN: llc < %s -march=msp430 | FileCheck %s
+; PR32769
+
+target triple = "msp430"
+
+; Test that CMP instruction is not removed by MachineCSE.
+;
+; CHECK-LABEL: @f
+; CHECK: cmp.w r15, r13
+; CHECK: cmp.w r15, r13
+; CHECK-NEXT: jeq .LBB0_2
+define i16 @f(i16, i16, i16, i16) {
+entry:
+  %4 = icmp ult i16 %1, %3
+  %5 = zext i1 %4 to i16
+  %6 = icmp ult i16 %0, %2
+  %7 = zext i1 %6 to i16
+  %8 = icmp eq i16 %1, %3
+  %out = select i1 %8, i16 %5, i16 %7
+  ret i16 %out
+}