[ICE]: panic=immediate-abort causes LLVM error on compiler_builtins on thumbv8m.main-none-eabi

Code

https://godbolt.org/z/WcvK9sTKW

MVE tarball attached: compiler-builtins-issue-mve.tar.gz

Use make to trigger the build

Meta

rustc --version --verbose:

rustc 1.95.0-nightly (39052daf9 2026-01-22)
binary: rustc
commit-hash: 39052daf937d46373ac29778e1b8853c52c0cc25
commit-date: 2026-01-22
host: x86_64-unknown-linux-gnu
release: 1.95.0-nightly
LLVM version: 21.1.8

Error output

$ RUST_BACKTRACE=1 RUSTFLAGS="-C target-feature=+v8.1m.main,-fpregs,-mve.fp,+mve -Zunstable-options -Cpanic=immediate-abort" cargo build --target thumbv8m.main-none-eabi -r -Zbuild-std
   Compiling compiler_builtins v0.1.160 (/home/bgarcia/.rustup/toolchains/nightly-2026-01-23-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/compiler-builtins/compiler-builtins)
   Compiling core v0.0.0 (/home/bgarcia/.rustup/toolchains/nightly-2026-01-23-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/core)
   Compiling compiler-builtins-issue-mve v0.1.0 (/home/bgarcia/tmp/compiler-builtins-issue-mve)
warning: unknown and unstable feature specified for `-Ctarget-feature`: `v8.1m.main`
  |
  = note: it is still passed through to the codegen backend, but use of this feature might be unsound and the behavior of this feature can change in the future
  = help: consider filing a feature request

warning: unstable feature specified for `-Ctarget-feature`: `fpregs`
  |
  = note: this feature is not stably supported; its behavior can change in the future

warning: unknown and unstable feature specified for `-Ctarget-feature`: `mve.fp`
  |
  = note: it is still passed through to the codegen backend, but use of this feature might be unsound and the behavior of this feature can change in the future
  = help: consider filing a feature request

warning: unknown and unstable feature specified for `-Ctarget-feature`: `mve`
  |
  = note: it is still passed through to the codegen backend, but use of this feature might be unsound and the behavior of this feature can change in the future
  = help: consider filing a feature request

warning: `compiler-builtins-issue-mve` (lib) generated 4 warnings
rustc-LLVM ERROR: Cannot select: 0x7eff0f10aa10: i32 = fp_to_sint_sat 0x7eff0f132f50, ValueType:ch:i32
  0x7eff0f132f50: f32 = bitcast 0x7eff0f134000
    0x7eff0f134000: i32,ch,glue = CopyFromReg 0x7eff0f134070, Register:i32 $r0, 0x7eff0f134070:1
      0x7eff0f134070: ch,glue = callseq_end 0x7eff0f1340e0, TargetConstant:i32<0>, TargetConstant:i32<-1>, 0x7eff0f1340e0:1
        0x7eff0f1340e0: ch,glue = ARMISD::CALL 0x7eff0f134150, TargetExternalSymbol:i32'__aeabi_fadd', Register:i32 $r0, Register:i32 $r1, RegisterMask:Untyped, 0x7eff0f134150:1
          0x7eff0f134150: ch,glue = CopyToReg 0x7eff0f1341c0, Register:i32 $r1, 0x7eff0f132850, 0x7eff0f1341c0:1
            0x7eff0f132850: i32 = bitcast 0x7eff0f10a9a0
              0x7eff0f10a9a0: f32,ch = CopyFromReg 0x7eff0f147d20, Register:f32 %4
            0x7eff0f1341c0: ch,glue = CopyToReg 0x7eff0f0c79a0, Register:i32 $r0, 0x7eff0f134540
              0x7eff0f134540: i32,ch,glue = CopyFromReg 0x7eff0f1345b0, Register:i32 $r0, 0x7eff0f1345b0:1
                0x7eff0f1345b0: ch,glue = callseq_end 0x7eff0f134620, TargetConstant:i32<0>, TargetConstant:i32<-1>, 0x7eff0f134620:1
                  0x7eff0f134620: ch,glue = ARMISD::CALL 0x7eff0f134690, TargetExternalSymbol:i32'__aeabi_fmul', Register:i32 $r0, Register:i32 $r1, RegisterMask:Untyped, 0x7eff0f134690:1

In function: _RNvNtNtNtCsdSVKkH0PCOu_17compiler_builtins4math9libm_math6expm1f6expm1f
error: could not compile `compiler_builtins` (lib)

Caused by:
  process didn't exit successfully: `/home/bgarcia/.rustup/toolchains/nightly-2026-01-23-x86_64-unknown-linux-gnu/bin/rustc --crate-name compiler_builtins --edition=2024 /home/bgarcia/.rustup/toolchains/nightly-2026-01-23-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/compiler-builtins/compiler-builtins/src/lib.rs --error-format=json --json=diagnostic-rendered-ansi,artifacts,future-incompat --diagnostic-width=238 --crate-type lib --emit=dep-info,metadata,link -C opt-level=3 -C embed-bitcode=no --cfg 'feature="compiler-builtins"' --cfg 'feature="default"' --cfg 'feature="rustc-dep-of-std"' --check-cfg 'cfg(docsrs,test)' --check-cfg 'cfg(feature, values("c", "compiler-builtins", "default", "mangled-names", "mem", "no-asm", "no-f16-f128", "rustc-dep-of-std", "unstable-public-internals"))' -C metadata=80bddacc4048cd74 -C extra-filename=-8829df885435518a --out-dir /home/bgarcia/tmp/compiler-builtins-issue-mve/target/thumbv8m.main-none-eabi/release/deps --target thumbv8m.main-none-eabi -C strip=debuginfo -Z force-unstable-if-unmarked -L dependency=/home/bgarcia/tmp/compiler-builtins-issue-mve/target/thumbv8m.main-none-eabi/release/deps -L dependency=/home/bgarcia/tmp/compiler-builtins-issue-mve/target/release/deps --extern core=/home/bgarcia/tmp/compiler-builtins-issue-mve/target/thumbv8m.main-none-eabi/release/deps/libcore-79b1c2732c45e7c4.rmeta --cap-lints allow -C target-feature=+v8.1m.main,-fpregs,-mve.fp,+mve -Zunstable-options -Cpanic=immediate-abort --cfg thumb --cfg f16_enabled --cfg f128_enabled --cfg intrinsics_enabled --cfg arch_enabled --cfg optimizations_enabled --cfg 'feature="unstable-intrinsics"' --cfg 'feature="mem"' --check-cfg 'cfg(__ashldi3, values("optimized-c"))' --check-cfg 'cfg(__ashlsi3, values("optimized-c"))' --check-cfg 'cfg(__ashrdi3, values("optimized-c"))' --check-cfg 'cfg(__ashrsi3, values("optimized-c"))' --check-cfg 'cfg(__bswapsi2, values("optimized-c"))' --check-cfg 'cfg(__bswapdi2, values("optimized-c"))' --check-cfg 'cfg(__bswapti2, values("optimized-c"))' --check-cfg 'cfg(__divdi3, values("optimized-c"))' --check-cfg 'cfg(__divsi3, values("optimized-c"))' --check-cfg 'cfg(__divmoddi4, values("optimized-c"))' --check-cfg 'cfg(__divmodsi4, values("optimized-c"))' --check-cfg 'cfg(__divmodsi4, values("optimized-c"))' --check-cfg 'cfg(__divmodti4, values("optimized-c"))' --check-cfg 'cfg(__lshrdi3, values("optimized-c"))' --check-cfg 'cfg(__lshrsi3, values("optimized-c"))' --check-cfg 'cfg(__moddi3, values("optimized-c"))' --check-cfg 'cfg(__modsi3, values("optimized-c"))' --check-cfg 'cfg(__muldi3, values("optimized-c"))' --check-cfg 'cfg(__udivdi3, values("optimized-c"))' --check-cfg 'cfg(__udivmoddi4, values("optimized-c"))' --check-cfg 'cfg(__udivmodsi4, values("optimized-c"))' --check-cfg 'cfg(__udivsi3, values("optimized-c"))' --check-cfg 'cfg(__umoddi3, values("optimized-c"))' --check-cfg 'cfg(__umodsi3, values("optimized-c"))' --check-cfg 'cfg(__aarch64_cas1_relax, values("optimized-c"))' --check-cfg 'cfg(__aarch64_cas1_acq, values("optimized-c"))' --check-cfg 'cfg(__aarch64_cas1_rel, values("optimized-c"))' --check-cfg 'cfg(__aarch64_cas1_acq_rel, values("optimized-c"))' --check-cfg 'cfg(__aarch64_cas2_relax, values("optimized-c"))' --check-cfg 'cfg(__aarch64_cas2_acq, values("optimized-c"))' --check-cfg 'cfg(__aarch64_cas2_rel, values("optimized-c"))' --check-cfg 'cfg(__aarch64_cas2_acq_rel, values("optimized-c"))' --check-cfg 'cfg(__aarch64_cas4_relax, values("optimized-c"))' --check-cfg 'cfg(__aarch64_cas4_acq, values("optimized-c"))' --check-cfg 'cfg(__aarch64_cas4_rel, values("optimized-c"))' --check-cfg 'cfg(__aarch64_cas4_acq_rel, values("optimized-c"))' --check-cfg 'cfg(__aarch64_cas8_relax, values("optimized-c"))' --check-cfg 'cfg(__aarch64_cas8_acq, values("optimized-c"))' --check-cfg 'cfg(__aarch64_cas8_rel, values("optimized-c"))' --check-cfg 'cfg(__aarch64_cas8_acq_rel, values("optimized-c"))' --check-cfg 'cfg(__aarch64_cas16_relax, values("optimized-c"))' --check-cfg 'cfg(__aarch64_cas16_acq, values("optimized-c"))' --check-cfg 'cfg(__aarch64_cas16_rel, values("optimized-c"))' --check-cfg 'cfg(__aarch64_cas16_acq_rel, values("optimized-c"))' --check-cfg 'cfg(__aarch64_ldadd1_relax, values("optimized-c"))' --check-cfg 'cfg(__aarch64_ldadd1_acq, values("optimized-c"))' --check-cfg 'cfg(__aarch64_ldadd1_rel, values("optimized-c"))' --check-cfg 'cfg(__aarch64_ldadd1_acq_rel, values("optimized-c"))' --check-cfg 'cfg(__aarch64_ldadd2_relax, values("optimized-c"))' --check-cfg 'cfg(__aarch64_ldadd2_acq, values("optimized-c"))' --check-cfg 'cfg(__aarch64_ldadd2_rel, values("optimized-c"))' --check-cfg 'cfg(__aarch64_ldadd2_acq_rel, values("optimized-c"))' --check-cfg 'cfg(__aarch64_ldadd4_relax, values("optimized-c"))' --check-cfg 'cfg(__aarch64_ldadd4_acq, values("optimized-c"))' --check-cfg 'cfg(__aarch64_ldadd4_rel, values("optimized-c"))' --check-cfg 'cfg(__aarch64_ldadd4_acq_rel, values("optimized-c"))' --check-cfg 'cfg(__aarch64_ldadd8_relax, values("optimized-c"))' --check-cfg 'cfg(__aarch64_ldadd8_acq, values("optimized-c"))' --check-cfg 'cfg(__aarch64_ldadd8_rel, values("optimized-c"))' --check-cfg 'cfg(__aarch64_ldadd8_acq_rel, values("optimized-c"))' --check-cfg 'cfg(__aarch64_ldclr1_relax, values("optimized-c"))' --check-cfg 'cfg(__aarch64_ldclr1_acq, values("optimized-c"))' --check-cfg 'cfg(__aarch64_ldclr1_rel, values("optimized-c"))' --check-cfg 'cfg(__aarch64_ldclr1_acq_rel, values("optimized-c"))' --check-cfg 'cfg(__aarch64_ldclr2_relax, values("optimized-c"))' --check-cfg 'cfg(__aarch64_ldclr2_acq, values("optimized-c"))' --check-cfg 'cfg(__aarch64_ldclr2_rel, values("optimized-c"))' --check-cfg 'cfg(__aarch64_ldclr2_acq_rel, values("optimized-c"))' --check-cfg 'cfg(__aarch64_ldclr4_relax, values("optimized-c"))' --check-cfg 'cfg(__aarch64_ldclr4_acq, values("optimized-c"))' --check-cfg 'cfg(__aarch64_ldclr4_rel, values("optimized-c"))' --check-cfg 'cfg(__aarch64_ldclr4_acq_rel, values("optimized-c"))' --check-cfg 'cfg(__aarch64_ldclr8_relax, values("optimized-c"))' --check-cfg 'cfg(__aarch64_ldclr8_acq, values("optimized-c"))' --check-cfg 'cfg(__aarch64_ldclr8_rel, values("optimized-c"))' --check-cfg 'cfg(__aarch64_ldclr8_acq_rel, values("optimized-c"))' --check-cfg 'cfg(__aarch64_ldeor1_relax, values("optimized-c"))' --check-cfg 'cfg(__aarch64_ldeor1_acq, values("optimized-c"))' --check-cfg 'cfg(__aarch64_ldeor1_rel, values("optimized-c"))' --check-cfg 'cfg(__aarch64_ldeor1_acq_rel, values("optimized-c"))' --check-cfg 'cfg(__aarch64_ldeor2_relax, values("optimized-c"))' --check-cfg 'cfg(__aarch64_ldeor2_acq, values("optimized-c"))' --check-cfg 'cfg(__aarch64_ldeor2_rel, values("optimized-c"))' --check-cfg 'cfg(__aarch64_ldeor2_acq_rel, values("optimized-c"))' --check-cfg 'cfg(__aarch64_ldeor4_relax, values("optimized-c"))' --check-cfg 'cfg(__aarch64_ldeor4_acq, values("optimized-c"))' --check-cfg 'cfg(__aarch64_ldeor4_rel, values("optimized-c"))' --check-cfg 'cfg(__aarch64_ldeor4_acq_rel, values("optimized-c"))' --check-cfg 'cfg(__aarch64_ldeor8_relax, values("optimized-c"))' --check-cfg 'cfg(__aarch64_ldeor8_acq, values("optimized-c"))' --check-cfg 'cfg(__aarch64_ldeor8_rel, values("optimized-c"))' --check-cfg 'cfg(__aarch64_ldeor8_acq_rel, values("optimized-c"))' --check-cfg 'cfg(__aarch64_ldset1_relax, values("optimized-c"))' --check-cfg 'cfg(__aarch64_ldset1_acq, values("optimized-c"))' --check-cfg 'cfg(__aarch64_ldset1_rel, values("optimized-c"))' --check-cfg 'cfg(__aarch64_ldset1_acq_rel, values("optimized-c"))' --check-cfg 'cfg(__aarch64_ldset2_relax, values("optimized-c"))' --check-cfg 'cfg(__aarch64_ldset2_acq, values("optimized-c"))' --check-cfg 'cfg(__aarch64_ldset2_rel, values("optimized-c"))' --check-cfg 'cfg(__aarch64_ldset2_acq_rel, values("optimized-c"))' --check-cfg 'cfg(__aarch64_ldset4_relax, values("optimized-c"))' --check-cfg 'cfg(__aarch64_ldset4_acq, values("optimized-c"))' --check-cfg 'cfg(__aarch64_ldset4_rel, values("optimized-c"))' --check-cfg 'cfg(__aarch64_ldset4_acq_rel, values("optimized-c"))' --check-cfg 'cfg(__aarch64_ldset8_relax, values("optimized-c"))' --check-cfg 'cfg(__aarch64_ldset8_acq, values("optimized-c"))' --check-cfg 'cfg(__aarch64_ldset8_rel, values("optimized-c"))' --check-cfg 'cfg(__aarch64_ldset8_acq_rel, values("optimized-c"))' --check-cfg 'cfg(__aarch64_swp1_relax, values("optimized-c"))' --check-cfg 'cfg(__aarch64_swp1_acq, values("optimized-c"))' --check-cfg 'cfg(__aarch64_swp1_rel, values("optimized-c"))' --check-cfg 'cfg(__aarch64_swp1_acq_rel, values("optimized-c"))' --check-cfg 'cfg(__aarch64_swp2_relax, values("optimized-c"))' --check-cfg 'cfg(__aarch64_swp2_acq, values("optimized-c"))' --check-cfg 'cfg(__aarch64_swp2_rel, values("optimized-c"))' --check-cfg 'cfg(__aarch64_swp2_acq_rel, values("optimized-c"))' --check-cfg 'cfg(__aarch64_swp4_relax, values("optimized-c"))' --check-cfg 'cfg(__aarch64_swp4_acq, values("optimized-c"))' --check-cfg 'cfg(__aarch64_swp4_rel, values("optimized-c"))' --check-cfg 'cfg(__aarch64_swp4_acq_rel, values("optimized-c"))' --check-cfg 'cfg(__aarch64_swp8_relax, values("optimized-c"))' --check-cfg 'cfg(__aarch64_swp8_acq, values("optimized-c"))' --check-cfg 'cfg(__aarch64_swp8_rel, values("optimized-c"))' --check-cfg 'cfg(__aarch64_swp8_acq_rel, values("optimized-c"))' --check-cfg 'cfg(target_feature, values("vis3"))' --check-cfg 'cfg(feature, values("checked"))' --check-cfg 'cfg(assert_no_panic)' --check-cfg 'cfg(thumb)' --check-cfg 'cfg(thumb_1)' --check-cfg 'cfg(x86_no_sse)' --check-cfg 'cfg(f16_enabled)' --check-cfg 'cfg(f128_enabled)' --check-cfg 'cfg(intrinsics_enabled)' --check-cfg 'cfg(arch_enabled)' --check-cfg 'cfg(optimizations_enabled)' --check-cfg 'cfg(feature, values("unstable-public-internals"))' --check-cfg 'cfg(optimizations_enabled)' --check-cfg 'cfg(kernel_user_helpers)' --check-cfg 'cfg(feature, values("mem-unaligned"))'` (exit status: 101)
make: *** [Makefile:2: all] Error 101

<backtrace>

Start with the attached compiler-builtins-issue-mve.tar.gz and run make to reproduce the failure, then inspect compiler-builtins/src/lib.rs around the expm1f function named in the LLVM error. Compare the result with the Godbolt example and verify that the thumbv8m.main-none-eabi build completes without the LLVM error.