[PATCH] D146084: [WebAssembly] Add comments on local.tee transformation
Heejin Ahn via Phabricator via llvm-commits
llvm-commits at lists.llvm.org
Tue Mar 14 13:09:24 PDT 2023
aheejin created this revision.
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We have a good comment on `TEE` transformation in `RegStackify`:
https://github.com/llvm/llvm-project/blob/547e3456660000a16fc5c2a2f819f1a2b5d35b5d/llvm/lib/Target/WebAssembly/WebAssemblyRegStackify.cpp#L613-L632
And I think it can be helpful to have some more comments on how the
`TEE`s createdin `RegStackify` are converted into `TEE_LOCAL`s.
Variable `OldReg` is changed to `DefReg` to be consistent with
`RegStackify`'s comment.
Repository:
rG LLVM Github Monorepo
https://reviews.llvm.org/D146084
Files:
llvm/lib/Target/WebAssembly/WebAssemblyExplicitLocals.cpp
Index: llvm/lib/Target/WebAssembly/WebAssemblyExplicitLocals.cpp
===================================================================
--- llvm/lib/Target/WebAssembly/WebAssemblyExplicitLocals.cpp
+++ llvm/lib/Target/WebAssembly/WebAssemblyExplicitLocals.cpp
@@ -267,15 +267,42 @@
// Replace tee instructions with local.tee. The difference is that tee
// instructions have two defs, while local.tee instructions have one def
// and an index of a local to write to.
+ //
+ // - Before:
+ // TeeReg, Reg = TEE DefReg
+ // INST ..., TeeReg, ...
+ // INST ..., Reg, ...
+ // INST ..., Reg, ...
+ // * DefReg: may or may not stackified
+ // * Reg: not stackified
+ // * TeeReg: stackified
+ //
+ // - After (when DefReg is already stackified):
+ // TeeReg = LOCAL_TEE LocalId1, DefReg
+ // INST ..., TeeReg, ...
+ // INST ..., Reg, ...
+ // INST ..., Reg, ...
+ // * Reg: mapped to LocalId1
+ // * TeeReg: stackified
+ //
+ // - After (when DefReg is not stackified):
+ // NewReg = LOCAL_GET LocalId1
+ // TeeReg = LOCAL_TEE LocalId2, NewReg
+ // INST ..., TeeReg, ...
+ // INST ..., Reg, ...
+ // INST ..., Reg, ...
+ // * DefReg: mapped to LocalId1
+ // * Reg: mapped to LocalId2
+ // * TeeReg: stackified
if (WebAssembly::isTee(MI.getOpcode())) {
assert(MFI.isVRegStackified(MI.getOperand(0).getReg()));
assert(!MFI.isVRegStackified(MI.getOperand(1).getReg()));
- Register OldReg = MI.getOperand(2).getReg();
- const TargetRegisterClass *RC = MRI.getRegClass(OldReg);
+ Register DefReg = MI.getOperand(2).getReg();
+ const TargetRegisterClass *RC = MRI.getRegClass(DefReg);
// Stackify the input if it isn't stackified yet.
- if (!MFI.isVRegStackified(OldReg)) {
- unsigned LocalId = getLocalId(Reg2Local, MFI, CurLocal, OldReg);
+ if (!MFI.isVRegStackified(DefReg)) {
+ unsigned LocalId = getLocalId(Reg2Local, MFI, CurLocal, DefReg);
Register NewReg = MRI.createVirtualRegister(RC);
unsigned Opc = getLocalGetOpcode(RC);
BuildMI(MBB, &MI, MI.getDebugLoc(), TII->get(Opc), NewReg)
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