[llvm] b64d7ba - [RISCV] Change the InstFormat for Zicbop prefetch instructions to InstFormatOther. (#148934)

[via llvm-commits]

Author: Craig Topper
Date: 2025-07-15T14:49:54-07:00
New Revision: b64d7baf9c0d37893ebabbe2539e725eb70b46e9

URL: https://github.com/llvm/llvm-project/commit/b64d7baf9c0d37893ebabbe2539e725eb70b46e9
DIFF: https://github.com/llvm/llvm-project/commit/b64d7baf9c0d37893ebabbe2539e725eb70b46e9.diff

LOG: [RISCV] Change the InstFormat for Zicbop prefetch instructions to InstFormatOther. (#148934)

The lower 5-bits of the immediate are not part of the address unlike
other InstFormatS instructions.

We use InstFormatS in RISCVRegisterInfo::needsFrameBaseReg and
RISCVRegisterInfo::getFrameIndexInstrOffset which is not aware of this
special encoding. Force the format to InstFormatOther so those functions
will ignore it.

InstFormatS is also used by relocation emission, but I don't believe we
ever emit these instructions with a relocation because of the encoding.

Added: 
    

Modified: 
    llvm/lib/Target/RISCV/RISCVInstrFormats.td
    llvm/lib/Target/RISCV/RISCVInstrInfoZicbo.td

Removed: 
    


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diff  --git a/llvm/lib/Target/RISCV/RISCVInstrFormats.td b/llvm/lib/Target/RISCV/RISCVInstrFormats.td
index b6b64b57b1b3e..e23001a3a0bff 100644
--- a/llvm/lib/Target/RISCV/RISCVInstrFormats.td
+++ b/llvm/lib/Target/RISCV/RISCVInstrFormats.td
@@ -193,7 +193,9 @@ class RVInstCommon<dag outs, dag ins, string opcodestr, string argstr,
   let AsmString = opcodestr # !if(!empty(argstr), "", "\t" # argstr);
   let Pattern = pattern;
 
-  let TSFlags{4-0} = format.Value;
+  InstFormat Format = format;
+
+  let TSFlags{4-0} = Format.Value;
 
   // Defaults
   RISCVVConstraint RVVConstraint = NoConstraint;

diff  --git a/llvm/lib/Target/RISCV/RISCVInstrInfoZicbo.td b/llvm/lib/Target/RISCV/RISCVInstrInfoZicbo.td
index 878b85b141578..0723b2f568a79 100644
--- a/llvm/lib/Target/RISCV/RISCVInstrInfoZicbo.td
+++ b/llvm/lib/Target/RISCV/RISCVInstrInfoZicbo.td
@@ -41,6 +41,7 @@ class Prefetch_ri<bits<5> optype, string opcodestr>
               opcodestr, "${imm12}(${rs1})"> {
   let Inst{11-7} = 0b00000;
   let rs2 = optype;
+  let Format = InstFormatOther; // this does not follow the normal S format.
 }
 
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