[SystemZ] Rework compare and branch support

Before the patch we took advantage of the fact that the compare and
branch are glued together in the selection DAG and fused them together
(where possible) while emitting them.  This seemed to work well in practice.
However, fusing the compare so early makes it harder to remove redundant
compares in cases where CC already has a suitable value.  This patch
therefore uses the peephole analyzeCompare/optimizeCompareInstr pair of
functions instead.

No behavioral change intended, but it paves the way for a later patch.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@187116 91177308-0d34-0410-b5e6-96231b3b80d8

test/CodeGen/SystemZ/int-cmp-02.ll

@@ -2,6 +2,8 @@
 ;
 ; RUN: llc < %s -mtriple=s390x-linux-gnu | FileCheck %s
 
+declare i32 @foo()
+
 ; Check register comparison.
 define double @f1(double %a, double %b, i32 %i1, i32 %i2) {
 ; CHECK-LABEL: f1:
@@ -159,3 +161,23 @@ define double @f11(double %a, double %b, i32 %i1, i64 %base, i64 %index) {
   %res = select i1 %cond, double %a, double %b
   ret double %res
 }
+
+; The first branch here got recreated by InsertBranch while splitting the
+; critical edge %entry->%while.body, which lost the kills information for CC.
+define void @f12(i32 %a, i32 %b) {
+; CHECK-LABEL: f12:
+; CHECK: crje %r2,
+; CHECK: crjlh %r2,
+; CHECK: br %r14
+entry:
+  %cmp11 = icmp eq i32 %a, %b
+  br i1 %cmp11, label %while.end, label %while.body
+
+while.body:
+  %c = call i32 @foo()
+  %cmp12 = icmp eq i32 %c, %b
+  br i1 %cmp12, label %while.end, label %while.body
+
+while.end:
+  ret void
+}