[PATCH] D75859: [CodeGenPrepare] Fold br(freeze(icmp x, const)) to br(icmp(freeze x, const))

[Juneyoung Lee via Phabricator via llvm-commits]

aqjune updated this revision to Diff 249271.
aqjune added a comment.

clang-format


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D75859/new/

https://reviews.llvm.org/D75859

Files:
  llvm/lib/CodeGen/CodeGenPrepare.cpp
  llvm/test/Transforms/CodeGenPrepare/X86/freeze-icmp.ll


Index: llvm/test/Transforms/CodeGenPrepare/X86/freeze-icmp.ll
===================================================================
--- /dev/null
+++ llvm/test/Transforms/CodeGenPrepare/X86/freeze-icmp.ll
@@ -0,0 +1,30 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
+; RUN: opt -S -codegenprepare < %s | FileCheck %s
+
+target triple = "x86_64-unknown-linux-gnu"
+
+define void @f(i32 %a) {
+; CHECK-LABEL: @f(
+; CHECK-NEXT:    [[FR:%.*]] = freeze i32 [[A:%.*]]
+; CHECK-NEXT:    [[C:%.*]] = icmp eq i32 [[FR]], 0
+; CHECK-NEXT:    br i1 [[C]], label [[A:%.*]], label [[B:%.*]]
+; CHECK:       A:
+; CHECK-NEXT:    call void @g1()
+; CHECK-NEXT:    ret void
+; CHECK:       B:
+; CHECK-NEXT:    call void @g2()
+; CHECK-NEXT:    ret void
+;
+  %c = icmp eq i32 %a, 0
+  %fr = freeze i1 %c
+  br i1 %fr, label %A, label %B
+A:
+  call void @g1()
+  ret void
+B:
+  call void @g2()
+  ret void
+}
+
+declare void @g1()
+declare void @g2()
Index: llvm/lib/CodeGen/CodeGenPrepare.cpp
===================================================================
--- llvm/lib/CodeGen/CodeGenPrepare.cpp
+++ llvm/lib/CodeGen/CodeGenPrepare.cpp
@@ -7191,6 +7191,28 @@
     return false;
   }
 
+  if (FreezeInst *FI = dyn_cast<FreezeInst>(I)) {
+    // br(freeze(icmp a, const)) -> br(icmp (freeze a), const)
+    // This helps generate efficient conditional jumps.
+    bool AllUsesAreBr = llvm::all_of(
+        FI->users(), [](const User *U) { return isa<BranchInst>(U); });
+    auto II = dyn_cast<ICmpInst>(FI->getOperand(0));
+    if (AllUsesAreBr && II && II->hasOneUse()) {
+      auto Op0 = II->getOperand(0), Op1 = II->getOperand(1);
+      bool Const0 = isa<ConstantInt>(Op0), Const1 = isa<ConstantInt>(Op1);
+      if (Const0 || Const1) {
+        FI->replaceAllUsesWith(II);
+        FI->eraseFromParent();
+        if (!Const0 || !Const1) {
+          Instruction *F = new FreezeInst(Const0 ? Op1 : Op0, "fr", II);
+          II->setOperand(Const0 ? 1 : 0, F);
+        }
+        return true;
+      }
+    }
+    return false;
+  }
+
   if (tryToSinkFreeOperands(I))
     return true;
 


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