forked from OSchip/llvm-project
1959ead525
The Select insn in BPF is expensive as BPF backend needs to resolve with conditionals. This patch set the getCmpSelInstrCost() to SCEVCheapExpansionBudget for Select insn to prevent some Select insn related optimizations. This change is motivated during bcc code review for https://github.com/iovisor/bcc/pull/3270 where IndVarSimplifyPass eventually caused generating the following asm code: ; for (i = 0; (i < VIRTIO_MAX_SGS) && (i < num); i++) { 14: 16 05 40 00 00 00 00 00 if w5 == 0 goto +64 <LBB0_6> 15: bc 51 00 00 00 00 00 00 w1 = w5 16: 04 01 00 00 ff ff ff ff w1 += -1 17: 67 05 00 00 20 00 00 00 r5 <<= 32 18: 77 05 00 00 20 00 00 00 r5 >>= 32 19: a6 01 01 00 05 00 00 00 if w1 < 5 goto +1 <LBB0_4> 20: b7 05 00 00 06 00 00 00 r5 = 6 00000000000000a8 <LBB0_4>: 21: b7 02 00 00 00 00 00 00 r2 = 0 22: b7 01 00 00 00 00 00 00 r1 = 0 ; for (i = 0; (i < VIRTIO_MAX_SGS) && (i < num); i++) { 23: 7b 1a e0 ff 00 00 00 00 *(u64 *)(r10 - 32) = r1 24: 7b 5a c0 ff 00 00 00 00 *(u64 *)(r10 - 64) = r5 Note that insn #15 has w1 = w5 and w1 is refined later but r5(w5) is eventually saved on stack at insn #24 for later use. This cause later verifier failures. With this change, IndVarSimplifyPass won't do the above transformation any more. Differential Revision: https://reviews.llvm.org/D97479 |
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| .. | ||
| Analysis | ||
| AsmParser | ||
| BinaryFormat | ||
| Bitcode | ||
| Bitstream | ||
| CodeGen | ||
| DWARFLinker | ||
| DebugInfo | ||
| Demangle | ||
| ExecutionEngine | ||
| Extensions | ||
| FileCheck | ||
| Frontend | ||
| FuzzMutate | ||
| Fuzzer | ||
| IR | ||
| IRReader | ||
| InterfaceStub | ||
| LTO | ||
| LineEditor | ||
| Linker | ||
| MC | ||
| MCA | ||
| Object | ||
| ObjectYAML | ||
| Option | ||
| Passes | ||
| ProfileData | ||
| Remarks | ||
| Support | ||
| TableGen | ||
| Target | ||
| Testing | ||
| TextAPI | ||
| ToolDrivers | ||
| Transforms | ||
| WindowsManifest | ||
| XRay | ||
| CMakeLists.txt | ||