Subzero: Fold icmp into br/select lowering.

tests_lit/llvm2ice_tests/8bit.pnacl.ll

 ; This tries to be a comprehensive test of i8 operations.
 
 ; RUN: %p2i --filetype=obj --disassemble -i %s --args -O2 | FileCheck %s
 ; RUN: %p2i --filetype=obj --disassemble -i %s --args -Om1 | FileCheck %s
 
+declare void @useInt(i32 %x)
+
 define internal i32 @add8Bit(i32 %a, i32 %b) {
 entry:
   %a_8 = trunc i32 %a to i8
   %b_8 = trunc i32 %b to i8
   %add = add i8 %b_8, %a_8
   %ret = zext i8 %add to i32
   ret i32 %ret
 }
 ; CHECK-LABEL: add8Bit
 ; CHECK: add {{[abcd]l}}
@@ skipping 255 matching lines @@
 ; CHECK-LABEL: icmp8BitMemSwapped
 ; CHECK: cmp {{[abcd]l|BYTE PTR}}
 
 define internal i32 @selectI8Var(i32 %a, i32 %b) {
 entry:
   %a_8 = trunc i32 %a to i8
   %b_8 = trunc i32 %b to i8
   %cmp = icmp slt i8 %a_8, %b_8
   %ret = select i1 %cmp, i8 %a_8, i8 %b_8
   %ret_ext = zext i8 %ret to i32
+  ; Create a "fake" use of %cmp to prevent O2 bool folding.
+  %d1 = zext i1 %cmp to i32
+  call void @useInt(i32 %d1)
   ret i32 %ret_ext
 }
 ; CHECK-LABEL: selectI8Var
 ; CHECK: cmp
 ; CHECK: setl
 ; CHECK: mov {{[a-d]l}}
 
 define internal i32 @testPhi8(i32 %arg, i32 %arg2, i32 %arg3, i32 %arg4, i32 %arg5, i32 %arg6, i32 %arg7, i32 %arg8, i32 %arg9, i32 %arg10) {
 entry:
   %trunc = trunc i32 %arg to i8
@@ skipping 66 matching lines @@
 ; CHECK: mov BYTE PTR {{.*}},{{[a-d]l}}
 
 define void @store_i8_const(i32 %addr_arg) {
 entry:
   %addr = inttoptr i32 %addr_arg to i8*
   store i8 123, i8* %addr, align 1
   ret void
 }
 ; CHECK-LABEL: store_i8_const
 ; CHECK: mov BYTE PTR {{.*}},0x7b