Subzero: Fix emission of 16-bit immediates.

tests_lit/assembler/x86/immediate_encodings.ll

 ; Tests various aspects of x86 immediate encoding. Some encodings are shorter.
 ; For example, the encoding is shorter for 8-bit immediates or when using EAX.
 ; This assumes that EAX is chosen as the first free register in O2 mode.
 
 ; RUN: %p2i -i %s --args -O2 --verbose none \
 ; RUN:   | llvm-mc -triple=i686-none-nacl -x86-asm-syntax=intel -filetype=obj \
 ; RUN:   | llvm-objdump -d --symbolize -x86-asm-syntax=intel - | FileCheck %s
 ; RUN: %p2i -i %s --args --verbose none | FileCheck --check-prefix=ERRORS %s
 ; RUN: %p2i -i %s --insts | %szdiff %s | FileCheck --check-prefix=DUMP %s
 
@@ skipping 26 matching lines @@
   %x2 = xor i8 %arg2_i8, 127
   %x3 = xor i8 %arg3_i8, 127
   %x4 = add i8 %x1, %x2
   %x5 = add i8 %x4, %x3
   %result = zext i8 %x5 to i32
   ret i32 %result
 }
 ; CHECK-LABEL: testXor8Imm8NotEAX
 ; CHECK: 80 f{{[1-3]}} 7f xor {{[^a]}}l, 127
 
+define internal i32 @testXor16Imm8(i32 %arg) {
+entry:
+  %arg_i16 = trunc i32 %arg to i16
+  %result_i16 = xor i16 %arg_i16, 127
+  %result = zext i16 %result_i16 to i32
+  ret i32 %result
+}
+; CHECK-LABEL: testXor16Imm8
+; CHECK: 66 83 f0 7f  xor ax, 127
+
+define internal i32 @testXor16Imm8Neg(i32 %arg) {
+entry:
+  %arg_i16 = trunc i32 %arg to i16
+  %result_i16 = xor i16 %arg_i16, -128
+  %result = zext i16 %result_i16 to i32
+  ret i32 %result
+}
+; CHECK-LABEL: testXor16Imm8Neg
+; CHECK: 66 83 f0 80  xor ax, 128
+
+define internal i32 @testXor16Imm16Eax(i32 %arg) {
+entry:
+  %arg_i16 = trunc i32 %arg to i16
+  %tmp = xor i16 %arg_i16, 1024
+  %result_i16 = add i16 %tmp, 1
+  %result = zext i16 %result_i16 to i32
+  ret i32 %result
+}
+; CHECK-LABEL: testXor16Imm16Eax
+; CHECK: 66 35 00 04  xor ax, 1024
+; CHECK-NEXT: add ax, 1
+
+define internal i32 @testXor16Imm16NegEax(i32 %arg) {
+entry:
+  %arg_i16 = trunc i32 %arg to i16
+  %tmp = xor i16 %arg_i16, -256
+  %result_i16 = add i16 %tmp, 1
+  %result = zext i16 %result_i16 to i32
+  ret i32 %result
+}
+; CHECK-LABEL: testXor16Imm16NegEax
+; CHECK: 66 35 00 ff  xor ax, 65280

[Jim Stichnoth, 2014/09/28 18:14:28]

Oddly, this part works correctly in master.

[jvoung (off chromium), 2014/09/29 01:16:56]

I think that llvm-objdump semi-silently ignored the error.

     124:       66 35 00 ff                                     xor     ax,
65280
     12a:       66 83 c0 01                                     add     ax, 1
     12e:       0f b7 c0                                        movzx   eax, ax

124 + 6 bytes is 12a, but it doesn't show the last two bytes! The llvm-objdump
does print the warning:

  
/...native_client/toolchain_build/out/llvm_x86_64_linux_work/Release+Asserts/bin/llvm-objdump:
warning: invalid instruction encoding

+; CHECK-NEXT: add ax, 1
+
+define internal i32 @testXor16Imm16NotEAX(i32 %arg_i32, i32 %arg2_i32, i32 %arg3_i32) {
+entry:
+  %arg = trunc i32 %arg_i32 to i16
+  %arg2 = trunc i32 %arg2_i32 to i16
+  %arg3 = trunc i32 %arg3_i32 to i16
+  %x = xor i16 %arg, 32767
+  %x2 = xor i16 %arg2, 32767
+  %x3 = xor i16 %arg3, 32767
+  %add1 = add i16 %x, %x2
+  %add2 = add i16 %add1, %x3
+  %result = zext i16 %add2 to i32
+  ret i32 %result
+}
+; CHECK-LABEL: testXor16Imm16NotEAX
+; CHECK: 66 81 f{{[1-3]}} ff 7f  xor {{[^a]}}x, 32767
+; CHECK-NEXT: 66 81 f{{[1-3]}} ff 7f  xor {{[^a]}}x, 32767
+
 define internal i32 @testXor32Imm8(i32 %arg) {
 entry:
   %result = xor i32 %arg, 127
   ret i32 %result
 }
 ; CHECK-LABEL: testXor32Imm8
 ; CHECK: 83 f0 7f   xor eax, 127
 
 define internal i32 @testXor32Imm8Neg(i32 %arg) {
 entry:
@@ skipping 48 matching lines @@
   %arg_i8 = trunc i32 %arg to i8
   %result_i8 = sub i8 %arg_i8, 125
   %result = zext i8 %result_i8 to i32
   ret i32 %result
 }
 ; CHECK-LABEL: testSub8Imm8
 ; CHECK: 2c 7d  sub al, 125
 
 ; ERRORS-NOT: ICE translation error
 ; DUMP-NOT: SZ