Stream: git-wasmtime

Topic: wasmtime / PR #13797 riscv64: Split clobber save/restore ...

Wasmtime GitHub notifications bot (Jul 01 2026 at 17:34):

rajeshgangam requested wasmtime-compiler-s390x-reviewers for a review on PR #13797.

Wasmtime GitHub notifications bot (Jul 01 2026 at 17:34):

rajeshgangam opened PR #13797 from rajeshgangam:clobber-save-restore to bytecodealliance:main:

Summary

• When the Zca extension is enabled, split the SP adjustment in function prologues/epilogues so callee-saved stores use small SP-relative offsets that fit in c.sdsp's 504-byte encoding range
• All callee-save stores/loads compress from 4-byte sd/ld to 2-byte c.sdsp/c.ldsp, saving ~28 bytes per function with 8 callee-saves
• Without Zca, the original combined SP decrement is preserved — zero behavior change on existing tests
• Adds isa_flags parameter to the ABIMachineSpec::gen_clobber_save and gen_clobber_restore trait methods so implementations can make ISA-specific decisions

Before (main, has_c enabled, 1KB frame + 8 callee-saves):

  addi sp, sp, -0x440           ; 4B  combined (clobber+frame)
  sd s1, 0x438(sp)              ; 4B  offset > 504, can't compress
  sd s2, 0x430(sp)              ; 4B
  ...

After (with Zca):

  c.addi16sp sp, -0x40          ; 2B  clobber only
  c.sdsp s1, 0x38(sp)           ; 2B  offset ≤ 504, compressed
  c.sdsp s2, 0x30(sp)           ; 2B
  ...
  addi sp, sp, -0x400           ; 4B  remaining frame

Fixes #7190.

Test plan

• [ ] All 235 riscv64 compile filetests pass
• [ ] All 116 aarch64, 181 x64, 101 s390x, 49 pulley filetests pass (no regressions from trait change)
• [ ] New c-clobber-save-restore.clif test with 3 cases: 100KB frame, 512B boundary, max callee-saves
• [ ] Existing 9 riscv64 test files have zero diff against main (non-Zca path unchanged)

:robot: Generated with Claude Code

Wasmtime GitHub notifications bot (Jul 01 2026 at 17:34):

rajeshgangam requested alexcrichton for a review on PR #13797.

Wasmtime GitHub notifications bot (Jul 01 2026 at 17:34):

rajeshgangam requested wasmtime-compiler-reviewers for a review on PR #13797.

Wasmtime GitHub notifications bot (Jul 01 2026 at 17:37):

rajeshgangam edited PR #13797:

Summary

• When the Zca extension is enabled, split the SP adjustment in function prologues/epilogues so callee-saved stores use small SP-relative offsets that fit in c.sdsp's 504-byte encoding range
• All callee-save stores/loads compress from 4-byte sd/ld to 2-byte c.sdsp/c.ldsp, saving ~28 bytes per function with 8 callee-saves
• Without Zca, the original combined SP decrement is preserved — zero behavior change on existing tests
• Adds isa_flags parameter to the ABIMachineSpec::gen_clobber_save and gen_clobber_restore trait methods so implementations can make ISA-specific decisions

Before (main, has_c enabled, 1KB frame + 8 callee-saves):

  addi sp, sp, -0x440           ; 4B  combined (clobber+frame)
  sd s1, 0x438(sp)              ; 4B  offset > 504, can't compress
  sd s2, 0x430(sp)              ; 4B
  ...

After (with Zca):

  c.addi16sp sp, -0x40          ; 2B  clobber only
  c.sdsp s1, 0x38(sp)           ; 2B  offset ≤ 504, compressed
  c.sdsp s2, 0x30(sp)           ; 2B
  ...
  addi sp, sp, -0x400           ; 4B  remaining frame

Fixes #7190.

Test plan

• [ ] All 235 riscv64 compile filetests pass
• [ ] All 116 aarch64, 181 x64, 101 s390x, 49 pulley filetests pass (no regressions from trait change)
• [ ] New c-clobber-save-restore.clif test with 3 cases: 100KB frame, 512B boundary, max callee-saves
• [ ] Existing 9 riscv64 test files have zero diff against main (non-Zca path unchanged)
  

Wasmtime GitHub notifications bot (Jul 01 2026 at 17:37):

rajeshgangam edited PR #13797:

Summary

• When the Zca extension is enabled, split the SP adjustment in function prologues/epilogues so callee-saved stores use small SP-relative offsets that fit in c.sdsp's 504-byte encoding range
• All callee-save stores/loads compress from 4-byte sd/ld to 2-byte c.sdsp/c.ldsp, saving ~28 bytes per function with 8 callee-saves
• Without Zca, the original combined SP decrement is preserved — zero behavior change on existing tests
• Adds isa_flags parameter to the ABIMachineSpec::gen_clobber_save and gen_clobber_restore trait methods so implementations can make ISA-specific decisions

Before (main, has_c enabled, 1KB frame + 8 callee-saves):

  addi sp, sp, -0x440           ; 4B  combined (clobber+frame)
  sd s1, 0x438(sp)              ; 4B  offset > 504, can't compress
  sd s2, 0x430(sp)              ; 4B
  ...

After (with Zca):

  c.addi16sp sp, -0x40          ; 2B  clobber only
  c.sdsp s1, 0x38(sp)           ; 2B  offset ≤ 504, compressed
  c.sdsp s2, 0x30(sp)           ; 2B
  ...
  addi sp, sp, -0x400           ; 4B  remaining frame

Fixes #7190.

Test plan

• [ ] All 235 riscv64 compile filetests pass
• [ ] All 116 aarch64, 181 x64, 101 s390x, 49 pulley filetests pass (no regressions from trait change)
• [ ] New c-clobber-save-restore.clif test with 3 cases: 100KB frame, 512B boundary, max callee-saves
• [ ] Existing 9 riscv64 test files have zero diff against main (non-Zca path unchanged)

Wasmtime GitHub notifications bot (Jul 01 2026 at 17:39):

rajeshgangam updated PR #13797.

Wasmtime GitHub notifications bot (Jul 01 2026 at 19:18):

github-actions[bot] added the label cranelift on PR #13797.

Wasmtime GitHub notifications bot (Jul 01 2026 at 19:18):

github-actions[bot] added the label cranelift:area:machinst on PR #13797.

Wasmtime GitHub notifications bot (Jul 01 2026 at 19:18):

github-actions[bot] added the label cranelift:area:aarch64 on PR #13797.

Wasmtime GitHub notifications bot (Jul 01 2026 at 19:18):

github-actions[bot] added the label cranelift:area:x64 on PR #13797.

Wasmtime GitHub notifications bot (Jul 02 2026 at 16:20):

fitzgen commented on PR #13797:

Hi, can you confirm that you are following our AI policy and have fully reviewed and understood the code here, and are willing to take responsibility for the code in the way that only a human can? Thanks.

Last updated: Jul 29 2026 at 05:03 UTC