ppc64: codegen tests (constants.go, mathbits.go) are eliminated by dead-code removal unless results escape

[jkrishmys]

Go version

go version go1.26-devel_2a71af11fc linux/ppc64le

Output of go env in your module/workspace:

GOARCH='linux/ppc64le'

What did you do?

Ran codegen tests at tip:
../bin/go test cmd/internal/testdir -run='Test/codegen/constants.go' -v -count=1
../bin/go test cmd/internal/testdir -run='Test/codegen/mathbits.go' -v -count=1

What did you see happen?

codegen/constants.go:12: linux/ppc64le/power10: opcode not found: "^MOVD\t[$]8193,"
codegen/constants.go:18: linux/ppc64le/power10: opcode not found: "^SLD\t[$]44,"
codegen/mathbits.go:741: linux/ppc64le/power10: opcode not found: "^ADDC\tR\d+,"
codegen/mathbits.go:743: linux/ppc64le/power10: opcode not found: "^ADDE"

What did you expect to see?

Expected the compiler to emit the expected PPC64 instructions matching the ppc64x: asm comments. Disassembly confirms that both shifted16BitConstants and contiguousMaskConstants, as well as Add64MultipleChains, were reduced to a single JMP LR because the results were not observable.

[jkrishmys]

recent failures:

https://ci.chromium.org/ui/p/golang/builders/ci/gotip-linux-ppc64le_power10/b8701998342382685457/overview

https://ci.chromium.org/ui/p/golang/builders/ci/gotip-linux-ppc64le_power9/b8701998214091165489/overview
https://ci.chromium.org/ui/p/golang/builders/ci/gotip-linux-ppc64le_power8/b8701996579544193505/overview

[gopherbot]

Change https://go.dev/cl/709435 mentions this issue: cmd/compile: fix PPC64x codegen tests eliminated by dead-code removal

[gabyhelp]

Related Issues

• cmd/internal/testdir:4_10: Test/codegen/constants.go failures [consistent failure] #75746
• cmd/internal/testdir: Test/codegen/shift.go failures [consistent failure] #70003 (closed)
• cmd/compile: branch elimination opportunites when comparing constants #37608
• cmd/compile: extra unused instructions for LoweredNilCheck #17211 (closed)
• test: all codegen tests are skipped #48247 (closed)
• x/arch/ppc64/ppc64asm: Fixes for ppc64 disassembly #17447 (closed)
• cmd/compile: ppc64 builds failing with ssa checker on #36723 (closed)
• cmd/internal/testdir:3_10: Test/codegen/mathbits.go failures [consistent failure] #75745
• cmd/compile: many new no-ops as a result of mid-stack inlining #29571

Related Code Changes

• cmd/internal/obj/ppc64: Fix ADUFFxxxx generation on aix/ppc64

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[jkrishmys]

CL 708916 fixes the above.