[RISCV] Change zext.w to be an alias of add.uw rd, rs1, x0 instead of pack.

[craig.topper]

Summary

This didn't make it into the published 0.93 spec, but it was the
intention.

But it is in the tex source as of this commit
https://github.com/riscv/riscv-bitmanip/commit/d172f029c074d47026a0c0d0f12d8b475c86a472

This means zext.w now requires Zba. Not sure if we should still use
pack if Zbp is enabled and Zba isn't. I'll leave that for the future
when pack is closer to being final.

[craig.topper]

Rebase

[craig.topper]

Rebase

[frasercrmck]

LGTM, but should we document these "extra" things we're doing on top of the published spec? I'm not sure where, but it might help someone reading the spec as written.

[asb]

LGTM, added two minor notes.

llvm/lib/Target/RISCV/RISCV.td

73

I think this is unused?

llvm/lib/Target/RISCV/RISCVInstrInfoB.td

513

Per Fraser's comment about noting these deviations, it might be worth adding a code comment here to note the deviation from the 0.93 spec.

[craig.topper]

Add note about 0.93 diverging from the spec.
Remove unused subtarget feature

llvm/lib/Target/RISCV/RISCV.td

def HasStdExtC : Predicate<"Subtarget->hasStdExtC()">,
                            "'C' (Compressed Instructions)">;
 
 def FeatureExtZba
     : SubtargetFeature<"experimental-zba", "HasStdExtZba", "true",
                        "'Zba' (Base 'B' Instructions)">;
 def HasStdExtZba : Predicate<"Subtarget->hasStdExtZba()">,
                              AssemblerPredicate<(all_of FeatureExtZba),
                              "'Zba' (Address calculation 'B' Instructions)">;
+def NotHasStdExtZba : Predicate<"!Subtarget->hasStdExtZba()">;
 
 def FeatureExtZbb
     : SubtargetFeature<"experimental-zbb", "HasStdExtZbb", "true",
                        "'Zbb' (Base 'B' Instructions)">;
 def HasStdExtZbb : Predicate<"Subtarget->hasStdExtZbb()">,
                              AssemblerPredicate<(all_of FeatureExtZbb),
                              "'Zbb' (Base 'B' Instructions)">;
 
 def FeatureExtZbc
     : SubtargetFeature<"experimental-zbc", "HasStdExtZbc", "true",
                        "'Zbc' (Carry-Less 'B' Instructions)">;
 def HasStdExtZbc : Predicate<"Subtarget->hasStdExtZbc()">,
                              AssemblerPredicate<(all_of FeatureExtZbc),
                              "'Zbc' (Carry-Less 'B' Instructions)">;
 
 def FeatureExtZbe
def HasStdExtZbt : Predicate<"Subtarget->hasStdExtZbt()">,
                              AssemblerPredicate<(all_of FeatureExtZbt),
                              "'Zbt' (Ternary 'B' Instructions)">;
 
 // Some instructions belong to both the basic and the permutation
 // subextensions. They should be enabled if either has been specified.
 def HasStdExtZbbOrZbp
     : Predicate<"Subtarget->hasStdExtZbb() || Subtarget->hasStdExtZbp()">,
                 AssemblerPredicate<(any_of FeatureExtZbb, FeatureExtZbp)>;
-def NotHasStdExtZbbOrZbp
-    : Predicate<"!(Subtarget->hasStdExtZbb() || Subtarget->hasStdExtZbp())">;
 
 def FeatureExtZbproposedc
     : SubtargetFeature<"experimental-zbproposedc", "HasStdExtZbproposedc", "true",
                        "'Zbproposedc' (Proposed Compressed 'B' Instructions)">;
 def HasStdExtZbproposedc : Predicate<"Subtarget->hasStdExtZbproposedc()">,
                            AssemblerPredicate<(all_of FeatureExtZbproposedc),
                            "'Zbproposedc' (Proposed Compressed 'B' Instructions)">;
 

llvm/lib/Target/RISCV/RISCVInstrInfo.td

 def ADJCALLSTACKDOWN : Pseudo<(outs), (ins i32imm:$amt1, i32imm:$amt2),
                               [(callseq_start timm:$amt1, timm:$amt2)]>;
 def ADJCALLSTACKUP   : Pseudo<(outs), (ins i32imm:$amt1, i32imm:$amt2),
                               [(callseq_end timm:$amt1, timm:$amt2)]>;
 } // Defs = [X2], Uses = [X2]
 
 /// RV64 patterns
 
-let Predicates = [IsRV64, NotHasStdExtZbbOrZbp] in
+let Predicates = [IsRV64, NotHasStdExtZba] in
 def : Pat<(and GPR:$rs1, 0xffffffff), (SRLI (SLLI GPR:$rs1, 32), 32)>;
 
 let Predicates = [IsRV64] in {
 
 /// sext and zext
 
 def : Pat<(sext_inreg GPR:$rs1, i32), (ADDIW GPR:$rs1, 0)>;
 

llvm/lib/Target/RISCV/RISCVInstrInfoB.td

 // The namespace RVBC exists to avoid encoding conflicts with the compressed
 // instructions c.addi16sp and c.lui already implemented in the C extension.
 
 let DecoderNamespace = "RVBC", Predicates = [HasStdExtZbproposedc, HasStdExtC] in {
 def C_NOT : RVBInstC<0b00, "c.not">, Sched<[]>;
 def C_NEG : RVBInstC<0b01, "c.neg">, Sched<[]>;
 } // DecoderNamespace = "RVBC", Predicates = [HasStdExtZbproposedc, HasStdExtC]
 
-let DecoderNamespace = "RVBC", Predicates = [HasStdExtZbproposedc, HasStdExtZbbOrZbp, HasStdExtC, IsRV64] in
+let DecoderNamespace = "RVBC", Predicates = [HasStdExtZbproposedc, HasStdExtZba, HasStdExtC, IsRV64] in
 def C_ZEXTW : RVBInstC<0b10, "c.zext.w">, Sched<[]>;
 
 //===----------------------------------------------------------------------===//
 // Pseudo Instructions
 //===----------------------------------------------------------------------===//
 
 let Predicates = [HasStdExtZbb, IsRV32] in {
 def : InstAlias<"zext.h $rd, $rs", (PACK GPR:$rd, GPR:$rs, X0)>;
 } // Predicates = [HasStdExtZbb, IsRV32]
 
 let Predicates = [HasStdExtZbb, IsRV64] in {
 def : InstAlias<"zext.h $rd, $rs", (PACKW GPR:$rd, GPR:$rs, X0)>;
-def : InstAlias<"zext.w $rd, $rs", (PACK GPR:$rd, GPR:$rs, X0)>;
 } // Predicates = [HasStdExtZbb, IsRV64]
 
+let Predicates = [HasStdExtZba, IsRV64] in {
+// NOTE: The 0.93 spec shows zext.w as an alias of pack/packw. It has been
+// changed to add.uw in a draft after 0.94.
+def : InstAlias<"zext.w $rd, $rs", (ADDUW GPR:$rd, GPR:$rs, X0)>;
+}
+
 let Predicates = [HasStdExtZbp] in {
 def : InstAlias<"rev.p $rd, $rs",  (GREVI GPR:$rd, GPR:$rs, 0b00001)>;
 def : InstAlias<"rev2.n $rd, $rs", (GREVI GPR:$rd, GPR:$rs, 0b00010)>;
 def : InstAlias<"rev.n $rd, $rs",  (GREVI GPR:$rd, GPR:$rs, 0b00011)>;
 def : InstAlias<"rev4.b $rd, $rs", (GREVI GPR:$rd, GPR:$rs, 0b00100)>;
 def : InstAlias<"rev2.b $rd, $rs", (GREVI GPR:$rd, GPR:$rs, 0b00110)>;
 def : InstAlias<"rev.b $rd, $rs",  (GREVI GPR:$rd, GPR:$rs, 0b00111)>;
 def : InstAlias<"rev8.h $rd, $rs", (GREVI GPR:$rd, GPR:$rs, 0b01000)>;

 //===----------------------------------------------------------------------===//
 let Predicates = [HasStdExtZbproposedc, HasStdExtC] in {
 def : CompressPat<(XORI GPRC:$rs1, GPRC:$rs1, -1),
                   (C_NOT GPRC:$rs1)>;
 def : CompressPat<(SUB GPRC:$rs1, X0, GPRC:$rs1),
                   (C_NEG GPRC:$rs1)>;
 } // Predicates = [HasStdExtZbproposedc, HasStdExtC]
 
-let Predicates = [HasStdExtZbproposedc, HasStdExtZbbOrZbp, HasStdExtC, IsRV64] in {
-def : CompressPat<(PACK GPRC:$rs1, GPRC:$rs1, X0),
+let Predicates = [HasStdExtZbproposedc, HasStdExtZba, HasStdExtC, IsRV64] in {
+def : CompressPat<(ADDUW GPRC:$rs1, GPRC:$rs1, X0),
                   (C_ZEXTW GPRC:$rs1)>;
 } // Predicates = [HasStdExtZbproposedc, HasStdExtC, IsRV64]
 
 //===----------------------------------------------------------------------===//
 // Codegen patterns
 //===----------------------------------------------------------------------===//
 
 let Predicates = [HasStdExtZbbOrZbp] in {

 def : Pat<(or (and (shl GPR:$rs2, (XLenVT 8)), 0xFF00),
               (and GPR:$rs1, 0x00FF)),
           (PACKH GPR:$rs1, GPR:$rs2)>;
 
 let Predicates = [HasStdExtZbbOrZbp, IsRV32] in
 def : Pat<(and GPR:$rs, 0x0000FFFF), (PACK GPR:$rs, X0)>;
 let Predicates = [HasStdExtZbbOrZbp, IsRV64] in {
 def : Pat<(and GPR:$rs, 0x000000000000FFFF), (PACKW GPR:$rs, X0)>;
-def : Pat<(and GPR:$rs, 0x00000000FFFFFFFF), (PACK GPR:$rs, X0)>;
 }
 
 let Predicates = [HasStdExtZbp, IsRV32] in {
 def : Pat<(or (or (and (shl GPR:$rs1, (i32 8)), (i32 0x00FF0000)),
                   (and GPR:$rs1, (i32 0xFF0000FF))),
               (and (srl GPR:$rs1, (i32 8)), (i32 0x0000FF00))),
           (SHFLI GPR:$rs1, (i32 8))>;
 def : Pat<(or (or (and (shl GPR:$rs1, (i32 4)), (i32 0x0F000F00)),

 
 let Predicates = [HasStdExtZba, IsRV64] in {
 def : Pat<(SLLIUWPat GPR:$rs1, uimm5:$shamt),
           (SLLIUW GPR:$rs1, uimm5:$shamt)>;
 def : Pat<(shl (and GPR:$rs1, 0xFFFFFFFF), uimm5:$shamt),
           (SLLIUW GPR:$rs1, uimm5:$shamt)>;
 def : Pat<(add (and GPR:$rs1, (i64 0xFFFFFFFF)), GPR:$rs2),
           (ADDUW GPR:$rs1, GPR:$rs2)>;
+def : Pat<(and GPR:$rs, 0x00000000FFFFFFFF), (ADDUW GPR:$rs, X0)>;
 }
 
 let Predicates = [HasStdExtZbp, IsRV64] in {
 def : Pat<(not (riscv_sllw (not GPR:$rs1), GPR:$rs2)),
           (SLOW GPR:$rs1, GPR:$rs2)>;
 def : Pat<(not (riscv_srlw (not GPR:$rs1), GPR:$rs2)),
           (SROW GPR:$rs1, GPR:$rs2)>;
 } // Predicates = [HasStdExtZbp, IsRV64]

llvm/test/CodeGen/RISCV/rv64Zba.ll

 ; RV64IBA-NEXT:    add.uw a0, a0, a1
 ; RV64IBA-NEXT:    lb a0, 0(a0)
 ; RV64IBA-NEXT:    ret
   %3 = zext i32 %0 to i64
   %4 = getelementptr inbounds i8, i8* %1, i64 %3
   %5 = load i8, i8* %4
   ret i8 %5
 }
+
+define i64 @zextw_i64(i64 %a) nounwind {
+; RV64I-LABEL: zextw_i64:
+; RV64I:       # %bb.0:
+; RV64I-NEXT:    slli a0, a0, 32
+; RV64I-NEXT:    srli a0, a0, 32
+; RV64I-NEXT:    ret
+;
+; RV64IB-LABEL: zextw_i64:
+; RV64IB:       # %bb.0:
+; RV64IB-NEXT:    zext.w a0, a0
+; RV64IB-NEXT:    ret
+;
+; RV64IBA-LABEL: zextw_i64:
+; RV64IBA:       # %bb.0:
+; RV64IBA-NEXT:    zext.w a0, a0
+; RV64IBA-NEXT:    ret
+  %and = and i64 %a, 4294967295
+  ret i64 %and
+}

llvm/test/CodeGen/RISCV/rv64Zbbp.ll

 ; RV64IBP-NEXT:    packh a0, a0, a1
 ; RV64IBP-NEXT:    ret
   %and = and i64 %a, 255
   %and1 = shl i64 %b, 8
   %shl = and i64 %and1, 65280
   %or = or i64 %shl, %and
   ret i64 %or
 }
-
-define i64 @zextw_i64(i64 %a) nounwind {
-; RV64I-LABEL: zextw_i64:
-; RV64I:       # %bb.0:
-; RV64I-NEXT:    slli a0, a0, 32
-; RV64I-NEXT:    srli a0, a0, 32
-; RV64I-NEXT:    ret
-;
-; RV64IB-LABEL: zextw_i64:
-; RV64IB:       # %bb.0:
-; RV64IB-NEXT:    zext.w a0, a0
-; RV64IB-NEXT:    ret
-;
-; RV64IBB-LABEL: zextw_i64:
-; RV64IBB:       # %bb.0:
-; RV64IBB-NEXT:    zext.w a0, a0
-; RV64IBB-NEXT:    ret
-;
-; RV64IBP-LABEL: zextw_i64:
-; RV64IBP:       # %bb.0:
-; RV64IBP-NEXT:    pack a0, a0, zero
-; RV64IBP-NEXT:    ret
-  %and = and i64 %a, 4294967295
-  ret i64 %and
-}

llvm/test/MC/RISCV/rv64b-aliases-valid.s

 # CHECK-S-OBJ-NOALIAS: andi t0, t1, 255
 # CHECK-S-OBJ: andi t0, t1, 255
 zext.b x5, x6
 
 # CHECK-S-OBJ-NOALIAS: packw t0, t1, zero
 # CHECK-S-OBJ: zext.h t0, t1
 zext.h x5, x6
 
-# CHECK-S-OBJ-NOALIAS: pack t0, t1, zero
+# CHECK-S-OBJ-NOALIAS: add.uw t0, t1, zero
 # CHECK-S-OBJ: zext.w t0, t1
 zext.w x5, x6
 
 # CHECK-S-OBJ-NOALIAS: grevi t0, t1, 1
 # CHECK-S-OBJ: rev.p t0, t1
 rev.p x5, x6
 
 # CHECK-S-OBJ-NOALIAS: grevi t0, t1, 2