[PATCH] D149839: [RISCV] def cm.jt as an alias inst of cm.jalt

[Xinlong Wu via Phabricator via llvm-commits]

VincentWu created this revision.
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This use `InstAlias` to fix the Decoding Conflict between `cm.jt` and `cm.jalt`.

The spec of Zc* defines `cm.jt` and `cm.jalt` has same encoding, the inst will be decode as `cm.jt` if `$index < 32`, it will be decode as  `cm.jalt` in other cases.

In previous implemention, it defined two separate instractions with same encoding. But there is no error when compiling.

but it will report Decoding Conflict when we define `cm.mva01s` in https://reviews.llvm.org/D132819 .

After testing, I think it may because decoding conflict between `cm.jt` and `cm.jalt`. Although it dosen't report error promptly. (I think it might be a issue when generating `RISCVGenDisassemblerTables.inc`)


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D149839

Files:
  llvm/lib/Target/RISCV/RISCVInstrInfoZc.td
  llvm/test/MC/RISCV/rv32zcmt-valid.s


Index: llvm/test/MC/RISCV/rv32zcmt-valid.s
===================================================================
--- llvm/test/MC/RISCV/rv32zcmt-valid.s
+++ llvm/test/MC/RISCV/rv32zcmt-valid.s
@@ -5,7 +5,7 @@
 # RUN:  -mattr=m < %s \
 # RUN:     | llvm-objdump --mattr=+experimental-zcmt\
 # RUN:  -M no-aliases -d -r - \
-# RUN:     | FileCheck --check-prefixes=CHECK-OBJ,CHECK-ASM-AND-OBJ %s
+# RUN:     | FileCheck --check-prefixes=CHECK-ASM-AND-OBJ %s
 # RUN: llvm-mc %s -triple=riscv64 -mattr=+experimental-zcmt\
 # RUN:  -riscv-no-aliases -show-encoding \
 # RUN:     | FileCheck -check-prefixes=CHECK-ASM,CHECK-ASM-AND-OBJ %s
@@ -13,7 +13,7 @@
 # RUN:  -mattr=m < %s \
 # RUN:     | llvm-objdump --mattr=+experimental-zcmt\
 # RUN:  -M no-aliases -d -r - \
-# RUN:     | FileCheck --check-prefixes=CHECK-OBJ,CHECK-ASM-AND-OBJ %s
+# RUN:     | FileCheck --check-prefixes=CHECK-ASM-AND-OBJ %s
 #
 # RUN: not llvm-mc -triple riscv32 \
 # RUN:     -riscv-no-aliases -show-encoding < %s 2>&1 \
@@ -22,13 +22,12 @@
 # RUN:     -riscv-no-aliases -show-encoding < %s 2>&1 \
 # RUN:     | FileCheck -check-prefixes=CHECK-NO-EXT %s
 
-# CHECK-ASM-AND-OBJ: cm.jt 1
+# CHECK-ASM-AND-OBJ: cm.jalt 1
 # CHECK-ASM: encoding: [0x06,0xa0]
 # CHECK-NO-EXT: error: instruction requires the following: 'Zcmt' (table jump instuctions for code-size reduction){{$}}
 cm.jt 1
 
-# CHECK-ASM: cm.jalt 1
-# CHECK-OBJ: cm.jt 1
+# CHECK-ASM-AND-OBJ: cm.jalt 1
 # CHECK-ASM: encoding: [0x06,0xa0]
 # CHECK-NO-EXT: error: instruction requires the following: 'Zcmt' (table jump instuctions for code-size reduction){{$}}
 cm.jalt 1
Index: llvm/lib/Target/RISCV/RISCVInstrInfoZc.td
===================================================================
--- llvm/lib/Target/RISCV/RISCVInstrInfoZc.td
+++ llvm/lib/Target/RISCV/RISCVInstrInfoZc.td
@@ -228,14 +228,7 @@
 }
 
 let Predicates = [HasStdExtZcmt],
-hasSideEffects = 0, mayLoad = 0, mayStore = 0 in {
-def CM_JT : RVInst16CJ<0b101, 0b10, (outs), (ins uimm5:$index),
-                       "cm.jt", "$index">{
-  bits<5> index;
-
-  let Inst{12-7} = 0b000000;
-  let Inst{6-2} = index;
-}
+hasSideEffects = 0, mayLoad = 0, mayStore = 0 in
 
 def CM_JALT : RVInst16CJ<0b101, 0b10, (outs), (ins uimm8:$index),
                          "cm.jalt", "$index">{
@@ -244,7 +237,6 @@
   let Inst{12-10} = 0b000;
   let Inst{9-2} = index;
 }
-} // Predicates = [HasStdExtZcmt]
 
 
 let Predicates = [HasStdExtZcb, HasStdExtMOrZmmul] in{
@@ -309,3 +301,6 @@
 def : InstAlias<"c.sb $rd, (${rs1})", (C_SB GPRC:$rd, GPRC:$rs1, 0)>;
 def : InstAlias<"c.sh $rd, (${rs1})", (C_SH GPRC:$rd, GPRC:$rs1, 0)>;
 }
+
+let Predicates = [HasStdExtZcmt] in
+def : InstAlias<"cm.jt $index",(CM_JALT uimm5:$index)>;


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