Add a pass to remove freeze instructions

Completely remove all freeze instructions before running any codegen
passes

Author: mshelego

IGC/VectorCompiler/include/GenX.h

@@ -162,6 +162,7 @@ ModulePass *createGenXDetectPointerArgPass();
 FunctionPass *createGenXLCECalculationPass();
 FunctionPass *createGenXFloatControlPass();
 ModulePass *createGenXCountIndirectStatelessPass();
+FunctionPass *createGenXUnfreezePass();
 
 namespace genx {
 

IGC/VectorCompiler/lib/GenXCodeGen/CMakeLists.txt

@@ -96,6 +96,7 @@ set(CODEGEN_SOURCES
   GenXTargetMachine.cpp
   GenXTidyControlFlow.cpp
   GenXUnbaling.cpp
+  GenXUnfreeze.cpp
   GenXUtil.cpp
   GenXVectorCombiner.cpp
   GenXVectorDecomposer.cpp

IGC/VectorCompiler/lib/GenXCodeGen/GenXPatternMatch.cpp

@@ -168,8 +168,6 @@ class GenXPatternMatch : public FunctionPass,
 
   void visitUDiv(BinaryOperator &I);
 
-  void visitFreezeInst(FreezeInst &I);
-
   bool runOnFunction(Function &F) override;
 
   bool isFpMadEnabled() const {
@@ -3671,16 +3669,6 @@ void GenXPatternMatch::visitURem(BinaryOperator &I) {
   return decomposeURemPow2(I);
 }
 
-// Clean up 'freeze' instances once dependent w/a's have been resolved.
-void GenXPatternMatch::visitFreezeInst(FreezeInst &I) {
-  if (I.use_empty())
-    return;
-
-  Value *Op = I.getOperand(0);
-  I.replaceAllUsesWith(Op);
-  Changed = true;
-}
-
 // Decompose predicate operand for large vector selects.
 bool GenXPatternMatch::decomposeSelect(Function *F) {
   const GenXSubtarget *ST = &getAnalysis<TargetPassConfig>()

IGC/VectorCompiler/lib/GenXCodeGen/GenXTargetMachine.cpp

@@ -246,6 +246,7 @@ void initializeGenXPasses(PassRegistry &registry) {
   initializeGenXLCECalculationPass(registry);
   initializeGenXFloatControlPass(registry);
   initializeGenXCountIndirectStatelessPass(registry);
+  initializeGenXUnfreezePass(registry);
   // WRITE HERE MORE PASSES IF IT'S NEEDED;
 }
 
@@ -504,6 +505,8 @@ bool GenXTargetMachine::addPassesToEmitFile(PassManagerBase &PM,
   vc::addPass(PM, PassConfig);
   const GenXBackendConfig &BackendConfig = PassConfig->getBackendConfig();
 
+  vc::addPass(PM, createGenXUnfreezePass());
+
   vc::addPass(PM, createGenXInitBiFConstantsPass());
   vc::addPass(PM, createGenXFixInvalidFuncNamePass());
 

IGC/VectorCompiler/lib/GenXCodeGen/GenXTargetMachine.h

@@ -271,6 +271,7 @@ void initializeGenXDetectPointerArgPass(PassRegistry &);
 void initializeGenXLCECalculationPass(PassRegistry &);
 void initializeGenXFloatControlPass(PassRegistry &);
 void initializeGenXCountIndirectStatelessPass(PassRegistry &);
+void initializeGenXUnfreezePass(PassRegistry &);
 } // End llvm namespace
 
 #endif

IGC/VectorCompiler/lib/GenXCodeGen/GenXUnfreeze.cpp

@@ -0,0 +1,65 @@
+/*========================== begin_copyright_notice ============================
+
+Copyright (C) 2025 Intel Corporation
+
+SPDX-License-Identifier: MIT
+
+============================= end_copyright_notice ===========================*/
+
+#include "GenX.h"
+
+#include "llvm/IR/InstVisitor.h"
+
+#define DEBUG_TYPE "GENX_UNFREEZE"
+
+using namespace llvm;
+
+namespace {
+class GenXUnfreeze : public FunctionPass, public InstVisitor<GenXUnfreeze> {
+  bool Changed = false;
+
+public:
+  static char ID;
+  explicit GenXUnfreeze() : FunctionPass(ID) {}
+
+  StringRef getPassName() const override { return "GenX unfreeze"; }
+
+  void getAnalysisUsage(AnalysisUsage &AU) const override {
+    AU.setPreservesCFG();
+  }
+
+  void visitFreezeInst(FreezeInst &FI);
+
+  bool runOnFunction(Function &F) override;
+};
+
+} // namespace
+
+char GenXUnfreeze::ID = 0;
+
+namespace llvm {
+void initializeGenXUnfreezePass(PassRegistry &);
+} // namespace llvm
+
+INITIALIZE_PASS_BEGIN(GenXUnfreeze, "GenXUnfreeze", "GenXUnfreeze", false,
+                      false)
+INITIALIZE_PASS_END(GenXUnfreeze, "GenXUnfreeze", "GenXUnfreeze", false, false)
+
+FunctionPass *llvm::createGenXUnfreezePass() {
+  initializeGenXUnfreezePass(*PassRegistry::getPassRegistry());
+  return new GenXUnfreeze();
+}
+
+void GenXUnfreeze::visitFreezeInst(FreezeInst &FI) {
+  if (FI.use_empty())
+    return;
+  auto *V = FI.getOperand(0);
+  FI.replaceAllUsesWith(V);
+  FI.eraseFromParent();
+  Changed = true;
+}
+
+bool GenXUnfreeze::runOnFunction(Function &F) {
+  visit(F);
+  return Changed;
+}

IGC/VectorCompiler/test/GenXUnfreeze/unfreeze.ll

@@ -0,0 +1,33 @@
+;=========================== begin_copyright_notice ============================
+;
+; Copyright (C) 2023-2025 Intel Corporation
+;
+; SPDX-License-Identifier: MIT
+;
+;============================ end_copyright_notice =============================
+
+; RUN: %opt %use_old_pass_manager% -GenXUnfreeze -march=genx64 -mcpu=XeLP -mtriple=spir64-unknown-unknown -S < %s | FileCheck %s
+
+; CHECK-NOT: freeze
+
+define spir_kernel void @test(i32 %arg) {
+  %w = add i32 %arg, undef
+  %x = freeze i32 %w
+  %y = add i32 %w, %w         ; undef
+  %z = add i32 %x, %x         ; even number because all uses of %x observe
+                              ; the same value
+  %x2 = freeze i32 %w
+  %cmp = icmp eq i32 %x, %x2  ; can be true or false
+
+  ; example with vectors
+  %v = add <2 x i32> <i32 undef, i32 poison>, zeroinitializer
+  %a = extractelement <2 x i32> %v, i32 0    ; undef
+  %b = extractelement <2 x i32> %v, i32 1    ; poison
+  %add = add i32 %a, %a                      ; undef
+
+  %v.fr = freeze <2 x i32> %v                ; element-wise freeze
+  %d = extractelement <2 x i32> %v.fr, i32 0 ; not undef
+  %add.f = add i32 %d, %d                    ; even number
+
+  ret void
+}