[RISCV] Add a tune feature to disable stripping W suffix (#86255)

We have a hidden option to disable it, but I'd like to make it a
tune feature.

For some implementations, instructions with W suffix would be less
costly as they only perform on 32 bits data. Though we may lose some
chances to compress.

Author: wangpc-pp

llvm/lib/Target/RISCV/RISCVFeatures.td

@@ -1226,6 +1226,10 @@ def TuneNoSinkSplatOperands
                        "false", "Disable sink splat operands to enable .vx, .vf,"
                        ".wx, and .wf instructions">;
 
+def TuneNoStripWSuffix
+    : SubtargetFeature<"no-strip-w-suffix", "EnableStripWSuffix", "false",
+                       "Disable strip W suffix">;
+
 def TuneConditionalCompressedMoveFusion
     : SubtargetFeature<"conditional-cmv-fusion", "HasConditionalCompressedMoveFusion",
                        "true", "Enable branch+c.mv fusion">;

llvm/lib/Target/RISCV/RISCVOptWInstrs.cpp

@@ -672,7 +672,7 @@ bool RISCVOptWInstrs::stripWSuffixes(MachineFunction &MF,
                                      const RISCVInstrInfo &TII,
                                      const RISCVSubtarget &ST,
                                      MachineRegisterInfo &MRI) {
-  if (DisableStripWSuffix)
+  if (DisableStripWSuffix || !ST.enableStripWSuffix())
     return false;
 
   bool MadeChange = false;

llvm/test/CodeGen/RISCV/strip-w-suffix.ll

@@ -0,0 +1,74 @@
+; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py
+; RUN: llc -mtriple=riscv64 -mattr=+m -verify-machineinstrs < %s \
+; RUN:   | FileCheck -check-prefixes=STRIP %s
+; RUN: llc -mtriple=riscv64 -mattr=+m,+no-strip-w-suffix -verify-machineinstrs < %s \
+; RUN:   | FileCheck -check-prefixes=NO-STRIP %s
+
+define i32 @addiw(i32 %a) {
+; STRIP-LABEL: addiw:
+; STRIP:       # %bb.0:
+; STRIP-NEXT:    lui a1, 1
+; STRIP-NEXT:    addi a1, a1, -1
+; STRIP-NEXT:    addw a0, a0, a1
+; STRIP-NEXT:    ret
+;
+; NO-STRIP-LABEL: addiw:
+; NO-STRIP:       # %bb.0:
+; NO-STRIP-NEXT:    lui a1, 1
+; NO-STRIP-NEXT:    addiw a1, a1, -1
+; NO-STRIP-NEXT:    addw a0, a0, a1
+; NO-STRIP-NEXT:    ret
+  %ret = add i32 %a, 4095
+  ret i32 %ret
+}
+
+define i32 @addw(i32 %a, i32 %b) {
+; STRIP-LABEL: addw:
+; STRIP:       # %bb.0:
+; STRIP-NEXT:    add a0, a0, a1
+; STRIP-NEXT:    addiw a0, a0, 1024
+; STRIP-NEXT:    ret
+;
+; NO-STRIP-LABEL: addw:
+; NO-STRIP:       # %bb.0:
+; NO-STRIP-NEXT:    addw a0, a0, a1
+; NO-STRIP-NEXT:    addiw a0, a0, 1024
+; NO-STRIP-NEXT:    ret
+  %add = add i32 %a, %b
+  %ret = add i32 %add, 1024
+  ret i32 %ret
+}
+
+define i32 @mulw(i32 %a, i32 %b) {
+; STRIP-LABEL: mulw:
+; STRIP:       # %bb.0:
+; STRIP-NEXT:    mul a0, a0, a1
+; STRIP-NEXT:    addiw a0, a0, 1024
+; STRIP-NEXT:    ret
+;
+; NO-STRIP-LABEL: mulw:
+; NO-STRIP:       # %bb.0:
+; NO-STRIP-NEXT:    mulw a0, a0, a1
+; NO-STRIP-NEXT:    addiw a0, a0, 1024
+; NO-STRIP-NEXT:    ret
+  %mul = mul i32 %a, %b
+  %ret = add i32 %mul, 1024
+  ret i32 %ret
+}
+
+define i32 @slliw(i32 %a) {
+; STRIP-LABEL: slliw:
+; STRIP:       # %bb.0:
+; STRIP-NEXT:    slli a0, a0, 1
+; STRIP-NEXT:    addiw a0, a0, 1024
+; STRIP-NEXT:    ret
+;
+; NO-STRIP-LABEL: slliw:
+; NO-STRIP:       # %bb.0:
+; NO-STRIP-NEXT:    slliw a0, a0, 1
+; NO-STRIP-NEXT:    addiw a0, a0, 1024
+; NO-STRIP-NEXT:    ret
+  %shl = shl i32 %a, 1
+  %ret = add i32 %shl, 1024
+  ret i32 %ret
+}