release/19.x: [LoongArch] Eliminate the redundant sign extension of division (#107971)

[llvmbot]

Backport 0f47e3a

Requested by: @heiher

[llvmbot]

@SixWeining What do you think about merging this PR to the release branch?

[llvmbot]

@llvm/pr-subscribers-backend-loongarch

Author: None (llvmbot)

Changes

Backport 0f47e3a

Requested by: @heiher

---

Full diff: https://github.com/llvm/llvm-project/pull/107990.diff

1 Files Affected:

• (modified) llvm/lib/Target/LoongArch/LoongArchOptWInstrs.cpp (+15)

diff --git a/llvm/lib/Target/LoongArch/LoongArchOptWInstrs.cpp b/llvm/lib/Target/LoongArch/LoongArchOptWInstrs.cpp
index abac69054f3b91..ab90409fdf47d0 100644
--- a/llvm/lib/Target/LoongArch/LoongArchOptWInstrs.cpp
+++ b/llvm/lib/Target/LoongArch/LoongArchOptWInstrs.cpp
@@ -637,6 +637,19 @@ static bool isSignExtendedW(Register SrcReg, const LoongArchSubtarget &ST,
         break;
       }
       return false;
+    // If all incoming values are sign-extended and all users only use
+    // the lower 32 bits, then convert them to W versions.
+    case LoongArch::DIV_D: {
+      if (!AddRegToWorkList(MI->getOperand(1).getReg()))
+        return false;
+      if (!AddRegToWorkList(MI->getOperand(2).getReg()))
+        return false;
+      if (hasAllWUsers(*MI, ST, MRI)) {
+        FixableDef.insert(MI);
+        break;
+      }
+      return false;
+    }
     }
   }
 
@@ -651,6 +664,8 @@ static unsigned getWOp(unsigned Opcode) {
     return LoongArch::ADDI_W;
   case LoongArch::ADD_D:
     return LoongArch::ADD_W;
+  case LoongArch::DIV_D:
+    return LoongArch::DIV_W;
   case LoongArch::LD_D:
   case LoongArch::LD_WU:
     return LoongArch::LD_W;

[heiher]

It seems that the patch created by the bot is incomplete. I'm not sure if it will automatically update after #107945 is merged. If not, it may be necessary to re-trigger the cherry-pick.

[tru]

Just re-run the cherry-pick comment on the updated SHA.

[github-actions]

@heiher (or anyone else). If you would like to add a note about this fix in the release notes (completely optional). Please reply to this comment with a one or two sentence description of the fix. When you are done, please add the release:note label to this PR.