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[GAS/ARM] Fix expansion of ldr pseudo instruction
authorThomas Preud'homme <thomas.preudhomme@arm.com>
Mon, 24 Apr 2017 13:49:48 +0000 (14:49 +0100)
committerThomas Preud'homme <thomas.preudhomme@arm.com>
Mon, 24 Apr 2017 13:51:24 +0000 (14:51 +0100)
The LDR rX, =cst pseudo-instruction suffers from two issues for loading
integer constants in Thumb mode:

- movs is used if the constant and register can be encoded using that
  instruction which leads to unexpected behavior due to its flag-setting
  behavior
- mov.w, movw and mvn are used for r13 (sp) and r15 (pc) but these
  encoding are marked as UNPREDICTABLE

This patch fixes those issues and update testing accordingly.

2017-04-24  Thomas Preud'homme  <thomas.preudhomme@arm.com>

gas/
* config/tc-arm.c (move_or_literal_pool): Remove code generating MOVS.
Forbid MOV.W and MOVW if destination is SP or PC.
* testsuite/gas/arm/thumb2_ldr_immediate_highregs_armv6t2.s: Explain
expectation of LDR not generating a MOVS for low registers and small
constants.  Add tests of MOVW generation.
* testsuite/gas/arm/thumb2_ldr_immediate_highregs_armv6t2.d: Update
expected disassembly.

gas/ChangeLog patch | blob | history
gas/config/tc-arm.c patch | blob | history
gas/testsuite/gas/arm/thumb2_ldr_immediate_highregs_armv6t2.d patch | blob | history
gas/testsuite/gas/arm/thumb2_ldr_immediate_highregs_armv6t2.s patch | blob | history

diff --git a/gas/ChangeLog b/gas/ChangeLog
index c5531a7686196c39ede5250472ff6e82201a4632..7c9697bd0454a1c20ede10c9784dd81f7291d471 100644 (file)
--- a/gas/ChangeLog
+++ b/gas/ChangeLog
@@ -1,3 +1,13 @@
+2017-04-24  Thomas Preud'homme  <thomas.preudhomme@arm.com>
+
+       * config/tc-arm.c (move_or_literal_pool): Remove code generating MOVS.
+       Forbid MOV.W and MOVW if destination is SP or PC.
+       * testsuite/gas/arm/thumb2_ldr_immediate_highregs_armv6t2.s: Explain
+       expectation of LDR not generating a MOVS for low registers and small
+       constants.  Add tests of MOVW generation.
+       * testsuite/gas/arm/thumb2_ldr_immediate_highregs_armv6t2.d: Update
+       expected disassembly.
+
 2017-04-22  Alan Modra  <amodra@gmail.com>
 
        * testsuite/gas/ppc/vle.s: Format.  Add se_rfgi and e_sc.
diff --git a/gas/config/tc-arm.c b/gas/config/tc-arm.c
index 83244b70473733801a44abfd3f7989992f409658..7e35c348d20bf4cea466ed4b19f3349e0b203be1 100644 (file)
--- a/gas/config/tc-arm.c
+++ b/gas/config/tc-arm.c
@@ -7959,17 +7959,13 @@ move_or_literal_pool (int i, enum lit_type t, bfd_boolean mode_3)
        {
          if (thumb_p)
            {
-             /* This can be encoded only for a low register.  */
-             if ((v & ~0xFF) == 0 && (inst.operands[i].reg < 8))
-               {
-                 /* This can be done with a mov(1) instruction.  */
-                 inst.instruction = T_OPCODE_MOV_I8 | (inst.operands[i].reg << 8);
-                 inst.instruction |= v;
-                 return TRUE;
-               }
+             /* LDR should not use lead in a flag-setting instruction being
+                chosen so we do not check whether movs can be used.  */
 
-             if (ARM_CPU_HAS_FEATURE (cpu_variant, arm_ext_v6t2)
+             if ((ARM_CPU_HAS_FEATURE (cpu_variant, arm_ext_v6t2)
                  || ARM_CPU_HAS_FEATURE (cpu_variant, arm_ext_v6t2_v8m))
+                 && inst.operands[i].reg != 13
+                 && inst.operands[i].reg != 15)
                {
                  /* Check if on thumb2 it can be done with a mov.w, mvn or
                     movw instruction.  */
diff --git a/gas/testsuite/gas/arm/thumb2_ldr_immediate_highregs_armv6t2.d b/gas/testsuite/gas/arm/thumb2_ldr_immediate_highregs_armv6t2.d
index 55b5f17887f94e894f5d02a4fcbb9c0d10d1227b..7afc1350e536798c48fabacb62adc079d5b13add 100644 (file)
--- a/gas/testsuite/gas/arm/thumb2_ldr_immediate_highregs_armv6t2.d
+++ b/gas/testsuite/gas/arm/thumb2_ldr_immediate_highregs_armv6t2.d
@@ -6,19 +6,23 @@
 .*: +file format .*arm.*
 
 Disassembly of section \.text:
-0[0-9a-f]+ <[^>]+> 2000[[:space:]]+movs[[:space:]]+r0, #0.*
-0[0-9a-f]+ <[^>]+> 2108[[:space:]]+movs[[:space:]]+r1, #8.*
-0[0-9a-f]+ <[^>]+> 2251[[:space:]]+movs[[:space:]]+r2, #81.*
-0[0-9a-f]+ <[^>]+> 231f[[:space:]]+movs[[:space:]]+r3, #31.*
-0[0-9a-f]+ <[^>]+> 242f[[:space:]]+movs[[:space:]]+r4, #47.*
-0[0-9a-f]+ <[^>]+> 253f[[:space:]]+movs[[:space:]]+r5, #63.*
-0[0-9a-f]+ <[^>]+> 2680[[:space:]]+movs[[:space:]]+r6, #128.*
-0[0-9a-f]+ <[^>]+> 27ff[[:space:]]+movs[[:space:]]+r7, #255.*
+0[0-9a-f]+ <[^>]+> f04f 0000[[:space:]]+mov\.w[[:space:]]+r0, #0.*
+0[0-9a-f]+ <[^>]+> f04f 0108[[:space:]]+mov\.w[[:space:]]+r1, #8.*
+0[0-9a-f]+ <[^>]+> f04f 0251[[:space:]]+mov\.w[[:space:]]+r2, #81.*
+0[0-9a-f]+ <[^>]+> f04f 031f[[:space:]]+mov\.w[[:space:]]+r3, #31.*
+0[0-9a-f]+ <[^>]+> f04f 042f[[:space:]]+mov\.w[[:space:]]+r4, #47.*
+0[0-9a-f]+ <[^>]+> f04f 053f[[:space:]]+mov\.w[[:space:]]+r5, #63.*
+0[0-9a-f]+ <[^>]+> f04f 0680[[:space:]]+mov\.w[[:space:]]+r6, #128.*
+0[0-9a-f]+ <[^>]+> f04f 07ff[[:space:]]+mov\.w[[:space:]]+r7, #255.*
 0[0-9a-f]+ <[^>]+> f04f 0800[[:space:]]+mov\.w[[:space:]]+r8, #0.*
 0[0-9a-f]+ <[^>]+> f04f 0908[[:space:]]+mov\.w[[:space:]]+r9, #8.*
 0[0-9a-f]+ <[^>]+> f04f 0a51[[:space:]]+mov\.w[[:space:]]+sl, #81.*
 0[0-9a-f]+ <[^>]+> f04f 0b1f[[:space:]]+mov\.w[[:space:]]+fp, #31.*
 0[0-9a-f]+ <[^>]+> f04f 0c2f[[:space:]]+mov\.w[[:space:]]+ip, #47.*
-0[0-9a-f]+ <[^>]+> f04f 0d3f[[:space:]]+mov\.w[[:space:]]+sp, #63.*
 0[0-9a-f]+ <[^>]+> f04f 0e80[[:space:]]+mov\.w[[:space:]]+lr, #128.*
-0[0-9a-f]+ <[^>]+> f04f 0fff[[:space:]]+mov\.w[[:space:]]+pc, #255.*
+0[0-9a-f]+ <[^>]+> f64f 78ff[[:space:]]+movw[[:space:]]+r8, #65535.*
+0[0-9a-f]+ <[^>]+> f24f 09f0[[:space:]]+movw[[:space:]]+r9, #61680.*
+0[0-9a-f]+ <[^>]+> f8df d004[[:space:]]+ldr\.w[[:space:]]+sp, \[pc, #4\].*
+0[0-9a-f]+ <[^>]+> f8df f004[[:space:]]+ldr\.w[[:space:]]+pc, \[pc, #4\].*
+0[0-9a-f]+ <[^>]+> 0000003f[[:space:]]+.word[[:space:]]+0x0000003f.*
+0[0-9a-f]+ <[^>]+> 000000ff[[:space:]]+.word[[:space:]]+0x000000ff.*
diff --git a/gas/testsuite/gas/arm/thumb2_ldr_immediate_highregs_armv6t2.s b/gas/testsuite/gas/arm/thumb2_ldr_immediate_highregs_armv6t2.s
index d2254101860f0fbc026dccb90076499cc2542b1a..b473857223603c946e4b5c923f4f9dfd110d5f6c 100644 (file)
--- a/gas/testsuite/gas/arm/thumb2_ldr_immediate_highregs_armv6t2.s
+++ b/gas/testsuite/gas/arm/thumb2_ldr_immediate_highregs_armv6t2.s
@@ -2,8 +2,8 @@
        .syntax unified
        .thumb_func
 thumb2_ldr:
-       # These can be encoded into movs since constant is small
-       # And register can be encoded in 3 bits
+       # These must be encoded into mov.w despite constant and register being
+       # small enough as ldr should not generate a flag-setting instruction.
        ldr r0,=0x00
        ldr r1,=0x08
        ldr r2,=0x51
@@ -12,13 +12,19 @@ thumb2_ldr:
        ldr r5,=0x3F
        ldr r6,=0x80
        ldr r7,=0xFF
-       # These shall be encoded into mov.w
-       # Since register cannot be encoded in 3 bits
+       # These shall be encoded into mov.w since register cannot be encoded in
+       # 3 bits
        ldr r8,=0x00
        ldr r9,=0x08
        ldr r10,=0x51
        ldr r11,=0x1F
        ldr r12,=0x2F
-       ldr r13,=0x3F
        ldr r14,=0x80
+       # These shall be encoded into movw since immediate cannot be encoded
+       # with mov.w
+       ldr r8,=0xFFFF
+       ldr r9,=0xF0F0
+       # These should be encoded as ldr since mov immediate is unpredictable
+       # for sp and pc
+       ldr r13,=0x3F
        ldr r15,=0xFF