[llvm][ARM] Allow MOVT and MOVW on the offset between two labels

[hwti]

In this case, the value is a constant, not an addend to a relocation.
So the "Relocation Not In Range" error must not be triggered.

Regression from PR #112877
Fixes #132322

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[llvmbot]

@llvm/pr-subscribers-backend-arm

Author: Loïc Yhuel (hwti)

Changes

In this case, the value is a constant, not an addend to a relocation.
So the "Relocation Not In Range" error must not be triggered.

Regression from PR #112877
Fixes #132322

---

Full diff: https://github.com/llvm/llvm-project/pull/168072.diff

2 Files Affected:

• (modified) llvm/lib/Target/ARM/MCTargetDesc/ARMAsmBackend.cpp (+1-1)
• (added) llvm/test/MC/ARM/arm-movt-movw-absolute-pass.s (+14)

diff --git a/llvm/lib/Target/ARM/MCTargetDesc/ARMAsmBackend.cpp b/llvm/lib/Target/ARM/MCTargetDesc/ARMAsmBackend.cpp
index f8196e460ae9c..02a7b1a3d0919 100644
--- a/llvm/lib/Target/ARM/MCTargetDesc/ARMAsmBackend.cpp
+++ b/llvm/lib/Target/ARM/MCTargetDesc/ARMAsmBackend.cpp
@@ -428,7 +428,7 @@ unsigned ARMAsmBackend::adjustFixupValue(const MCAssembler &Asm,
   // signed 16bit range.
   if ((Kind == ARM::fixup_arm_movw_lo16 || Kind == ARM::fixup_arm_movt_hi16 ||
        Kind == ARM::fixup_t2_movw_lo16 || Kind == ARM::fixup_t2_movt_hi16) &&
-      (Addend < minIntN(16) || Addend > maxIntN(16))) {
+      !Target.isAbsolute() && (Addend < minIntN(16) || Addend > maxIntN(16))) {
     Ctx.reportError(Fixup.getLoc(), "Relocation Not In Range");
     return 0;
   }
diff --git a/llvm/test/MC/ARM/arm-movt-movw-absolute-pass.s b/llvm/test/MC/ARM/arm-movt-movw-absolute-pass.s
new file mode 100644
index 0000000000000..ed888a0a4aaae
--- /dev/null
+++ b/llvm/test/MC/ARM/arm-movt-movw-absolute-pass.s
@@ -0,0 +1,14 @@
+@RUN: llvm-mc -triple armv7-eabi -filetype obj -o - %s 2>&1 | FileCheck %s
+
+    .text
+a:
+    movw    r1, #:lower16:b - a + 65536
+    movt    r1, #:upper16:b - a + 65536
+b:
+
+@CHECK-NOT: error: Relocation Not In Range
+@CHECK-NOT: movw    r1, #:lower16:b - a + 65536
+@CHECK-NOT: ^
+@CHECK-NOT: error: Relocation Not In Range
+@CHECK-NOT: movt    r1, #:upper16:b - a + 65536
+@CHECK-NOT: ^

[hwti]

cc @Stylie777 @DavidSpickett @jthackray from the PR which added the Relocation Not In Range error

[efriedma-quic]

Instead of checking for the error message, please just check that we generate the correct instruction encoding.

[hwti]

I used arm-movt-movw-range-pass.s as a model.

llvm-mc -show-encoding produces :

        movw    r1, :lower16:((b-a)+65536)      @ encoding: [A,0x10'A',0b0000AAAA,0xe3]
                                        @   fixup A - offset: 0, value: (b-a)+65536, kind: fixup_arm_movw_lo16
        movt    r1, :upper16:((b-a)+65536)      @ encoding: [A,0x10'A',0b0100AAAA,0xe3]
                                        @   fixup A - offset: 0, value: (b-a)+65536, kind: fixup_arm_movt_hi16

so it doesn't show the value is resolved.

Do you want a test with llvm-objdump, like :

@RUN: llvm-mc -triple armv7-eabi -filetype obj %s -o - | llvm-objdump -d --triple armv7-eabi - | FileCheck %s

a:
    movw    r1, #:lower16:b - a + 65536
    movt    r1, #:upper16:b - a + 65536
b:

@CHECK: 0: e3001008 movw r1, #0x8
@CHECK: 4: e3401001 movt r1, #0x1

?

But it actually tests more, so I don't know know if you meant with "just check ...".

[efriedma-quic]

Something with llvm-objdump seems fine, yes.

[efriedma-quic]

Maybe could use IsResolved here instead? I guess it's basically the same thing in this context.

[hwti]

OK, changed to !IsResolved.

[github-actions]

🐧 Linux x64 Test Results

• 186275 tests passed
• 4849 tests skipped

[efriedma-quic]

LGTM

[github-actions]

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