Subzero: Transform suitable Load/Arith/Store sequences into RMW ops.

tests_lit/llvm2ice_tests/ias-multi-reloc.ll

 ; Tests the integrated assembler for instructions with multiple
 ; relocations.
 
 ; RUN: %if --need=allow_dump --command %p2i -i %s --args -O2 \
 ; RUN:   | %if --need=allow_dump --command FileCheck %s
 
 ; char global_char;
 ; char *p_global_char;
 ; void dummy();
 ; void store_immediate_to_global() { p_global_char = &global_char; }
 ; void add_in_place() { p_global_char += (int)&global_char; }
 ; void cmp_global_immediate() { if (p_global_char == &global_char) dummy(); }
 
 @global_char = internal global [1 x i8] zeroinitializer, align 1
 @p_global_char = internal global [4 x i8] zeroinitializer, align 4
 declare void @dummy()
 
 define internal void @store_immediate_to_global() {
 entry:
   %p_global_char.bc = bitcast [4 x i8]* @p_global_char to i32*
   %expanded1 = ptrtoint [1 x i8]* @global_char to i32
   store i32 %expanded1, i32* %p_global_char.bc, align 1
   ret void
 }
 ; CHECK-LABEL: store_immediate_to_global
 ; CHECK: .long p_global_char
 ; CHECK: .long global_char
 
+; Also exercises the RMW add operation.
 define internal void @add_in_place() {
 entry:
   %p_global_char.bc = bitcast [4 x i8]* @p_global_char to i32*
   %0 = load i32, i32* %p_global_char.bc, align 1
   %expanded1 = ptrtoint [1 x i8]* @global_char to i32
   %gep = add i32 %0, %expanded1
   %p_global_char.bc3 = bitcast [4 x i8]* @p_global_char to i32*
   store i32 %gep, i32* %p_global_char.bc3, align 1
   ret void
 }
 ; CHECK-LABEL: add_in_place
-; CHECK: .long global_char
 ; CHECK: .long p_global_char
+; CHECK-NEXT: .long global_char
 
 define internal void @cmp_global_immediate() {
 entry:
   %p_global_char.bc = bitcast [4 x i8]* @p_global_char to i32*
   %0 = load i32, i32* %p_global_char.bc, align 1
   %expanded1 = ptrtoint [1 x i8]* @global_char to i32
   %cmp = icmp eq i32 %0, %expanded1
   br i1 %cmp, label %if.then, label %if.end
 
 if.then:                                          ; preds = %entry
   tail call void @dummy()
   br label %if.end
 
 if.end:                                           ; preds = %if.then, %entry
   ret void
 }
 ; CHECK-LABEL: cmp_global_immediate
 ; CHECK: .long p_global_char
 ; CHECK: .long global_char
 ; CHECK: .long dummy