Subzero. ARM32. Improve constant lowering.

tests_lit/llvm2ice_tests/bool-folding.ll

 ; This tests the optimization where producers and consumers of i1 (bool)
 ; variables are combined to implicitly use flags instead of explicitly using
 ; stack or register variables.
 
 ; RUN: %p2i -i %s --filetype=obj --disassemble --args -O2 \
 ; RUN:   -allow-externally-defined-symbols | FileCheck %s
 
 ; RUN: %if --need=allow_dump --need=target_ARM32 --command %p2i --filetype=asm \
 ; RUN:   --target arm32 -i %s --args -O2 --skip-unimplemented \
 ; RUN:   -allow-externally-defined-symbols \
@@ skipping 151 matching lines @@
   %cmp1 = icmp slt i32 undef, %arg1_trunc
   %result = select i1 %cmp1, i64 %arg1, i64 undef
   ret i64 %result
 }
 ; CHECK-LABEL: fold_cmp_select_64_undef
 ; CHECK: cmp
 ; CHECK: cmovl
 ; CHECK: cmovl
 ; ARM32-LABEL: fold_cmp_select_64_undef
 ; ARM32: mov
-; ARM32: mov
-; ARM32: cmp {{r[0-9]+}}, r0
+; ARM32: rsbs r{{[0-9]+}}, r{{[0-9]+}}, #0
 ; ARM32: movlt
 ; ARM32: movlt
 ; ARM32: bx lr
 
 
 ; Cmp/select folding with intervening instructions.
 define internal i32 @fold_cmp_select_intervening_insts(i32 %arg1, i32 %arg2) {
 entry:
   %cmp1 = icmp slt i32 %arg1, %arg2
   call void @use_value(i32 %arg1)
@@ skipping 237 matching lines @@
 ; ARM32: tst r0, #1
 ; ARM32: bne
 ; ARM32: tst r1, #1
 ; ARM32: beq
 ; ARM32: tst r2, #1
 ; ARM32: bne     {{.*}}target_true
 ; ARM32: tst     r3, #1
 ; ARM32: beq     {{.*}}target_false
 ; ARM32: tst     r4, #1
 ; ARM32: beq     {{.*}}target_false