From e63898e4a8dc9d948caa432bb350b0237e74d8e5 Mon Sep 17 00:00:00 2001
From: Morris Hafner <mhafner@nvidia.com>
Date: Fri, 23 May 2025 18:33:33 +0200
Subject: [PATCH] [CIR] Generate SelectOp instead of TernaryOp for if cheap
 enough to evaluate unconditionally

---
 clang/lib/CIR/CodeGen/CIRGenExprScalar.cpp | 36 ++++++--------
 clang/test/CIR/CodeGen/ternary.c           |  7 +++
 clang/test/CIR/Transforms/ternary-fold.cpp | 56 ----------------------
 3 files changed, 21 insertions(+), 78 deletions(-)
 delete mode 100644 clang/test/CIR/Transforms/ternary-fold.cpp

diff --git a/clang/lib/CIR/CodeGen/CIRGenExprScalar.cpp b/clang/lib/CIR/CodeGen/CIRGenExprScalar.cpp
index 8a81b60c1c2b..3e47d4e10486 100644
--- a/clang/lib/CIR/CodeGen/CIRGenExprScalar.cpp
+++ b/clang/lib/CIR/CodeGen/CIRGenExprScalar.cpp
@@ -2516,30 +2516,22 @@ mlir::Value ScalarExprEmitter::VisitAbstractConditionalOperator(
   if (isCheapEnoughToEvaluateUnconditionally(lhsExpr, CGF) &&
       isCheapEnoughToEvaluateUnconditionally(rhsExpr, CGF)) {
     bool lhsIsVoid = false;
-    auto condV = CGF.evaluateExprAsBool(condExpr);
+    mlir::Value condV = CGF.evaluateExprAsBool(condExpr);
     assert(!cir::MissingFeatures::incrementProfileCounter());
 
-    return builder
-        .create<cir::TernaryOp>(
-            loc, condV, /*thenBuilder=*/
-            [&](mlir::OpBuilder &b, mlir::Location loc) {
-              auto lhs = Visit(lhsExpr);
-              if (!lhs) {
-                lhs = builder.getNullValue(CGF.VoidTy, loc);
-                lhsIsVoid = true;
-              }
-              builder.create<cir::YieldOp>(loc, lhs);
-            },
-            /*elseBuilder=*/
-            [&](mlir::OpBuilder &b, mlir::Location loc) {
-              auto rhs = Visit(rhsExpr);
-              if (lhsIsVoid) {
-                assert(!rhs && "lhs and rhs types must match");
-                rhs = builder.getNullValue(CGF.VoidTy, loc);
-              }
-              builder.create<cir::YieldOp>(loc, rhs);
-            })
-        .getResult();
+    mlir::Value lhs = Visit(lhsExpr);
+    if (!lhs) {
+      lhs = builder.getNullValue(CGF.VoidTy, loc);
+      lhsIsVoid = true;
+    }
+
+    mlir::Value rhs = Visit(rhsExpr);
+    if (lhsIsVoid) {
+      assert(!rhs && "lhs and rhs types must match");
+      rhs = builder.getNullValue(CGF.VoidTy, loc);
+    }
+
+    return builder.createSelect(loc, condV, lhs, rhs);
   }
 
   mlir::Value condV = CGF.emitOpOnBoolExpr(loc, condExpr);
diff --git a/clang/test/CIR/CodeGen/ternary.c b/clang/test/CIR/CodeGen/ternary.c
index 16c20460f102..ee6c71549576 100644
--- a/clang/test/CIR/CodeGen/ternary.c
+++ b/clang/test/CIR/CodeGen/ternary.c
@@ -13,3 +13,10 @@ double f1(int cond, int n, ...) {
 
 // Fine enough to check it passes the verifying.
 // CIR: cir.ternary
+
+int unconditional_evaluation(_Bool cond) {
+  return cond ? 123 : 456;
+  // CIR: %[[TRUE_CONST:.+]] = cir.const #cir.int<123>
+  // CIR: %[[FALSE_CONST:.+]] = cir.const #cir.int<456>
+  // CIR: cir.select if {{.+}} then %[[TRUE_CONST]] else %[[FALSE_CONST]] : (!cir.bool, !s32i, !s32i) -> !s32i
+}
diff --git a/clang/test/CIR/Transforms/ternary-fold.cpp b/clang/test/CIR/Transforms/ternary-fold.cpp
deleted file mode 100644
index eadc74f99a17..000000000000
--- a/clang/test/CIR/Transforms/ternary-fold.cpp
+++ /dev/null
@@ -1,56 +0,0 @@
-// RUN: %clang_cc1 -triple x86_64-unknown-linux-gnu -O1 -fclangir -emit-cir -mmlir --mlir-print-ir-before=cir-canonicalize %s -o %t1.cir 2>&1 | FileCheck -check-prefix=CIR-BEFORE %s
-// RUN: %clang_cc1 -triple x86_64-unknown-linux-gnu -O1 -fclangir -emit-cir -mmlir --mlir-print-ir-after=cir-simplify %s -o %t2.cir 2>&1 | FileCheck -check-prefix=CIR-AFTER %s
-// RUN: %clang_cc1 -triple x86_64-unknown-linux-gnu -O1 -fclangir -emit-llvm %s -o %t.ll 
-// RUN: FileCheck --input-file=%t.ll --check-prefix=LLVM %s
-
-int test(bool x) {
-  return x ? 1 : 2;
-}
-
-//      CIR-BEFORE: cir.func @_Z4testb
-//      CIR-BEFORE:   %{{.+}} = cir.ternary(%{{.+}}, true {
-// CIR-BEFORE-NEXT:     %[[#A:]] = cir.const #cir.int<1> : !s32i
-// CIR-BEFORE-NEXT:     cir.yield %[[#A]] : !s32i
-// CIR-BEFORE-NEXT:   }, false {
-// CIR-BEFORE-NEXT:     %[[#B:]] = cir.const #cir.int<2> : !s32i
-// CIR-BEFORE-NEXT:     cir.yield %[[#B]] : !s32i
-// CIR-BEFORE-NEXT:   }) : (!cir.bool) -> !s32i
-//      CIR-BEFORE: }
-
-//      CIR-AFTER: cir.func @_Z4testb
-//      CIR-AFTER:   %[[#A:]] = cir.const #cir.int<1> : !s32i
-// CIR-AFTER-NEXT:   %[[#B:]] = cir.const #cir.int<2> : !s32i
-// CIR-AFTER-NEXT:   %{{.+}} = cir.select if %{{.+}} then %[[#A]] else %[[#B]] : (!cir.bool, !s32i, !s32i) -> !s32i
-//      CIR-AFTER: }
-
-// LLVM: @_Z4testb
-// LLVM:   %{{.+}} = select i1 %{{.+}}, i32 1, i32 2
-// LLVM: }
-
-int test2(bool cond) {
-  constexpr int x = 1;
-  constexpr int y = 2;
-  return cond ? x : y;
-}
-
-//      CIR-BEFORE: cir.func @_Z5test2b
-//      CIR-BEFORE:   %[[#COND:]] = cir.load{{.*}} %{{.+}} : !cir.ptr<!cir.bool>, !cir.bool
-// CIR-BEFORE-NEXT:   %{{.+}} = cir.ternary(%[[#COND]], true {
-// CIR-BEFORE-NEXT:     %[[#A:]] = cir.const #cir.int<1> : !s32i
-// CIR-BEFORE-NEXT:     cir.yield %[[#A]] : !s32i
-// CIR-BEFORE-NEXT:   }, false {
-// CIR-BEFORE-NEXT:     %[[#B:]] = cir.const #cir.int<2> : !s32i
-// CIR-BEFORE-NEXT:     cir.yield %[[#B]] : !s32i
-// CIR-BEFORE-NEXT:   }) : (!cir.bool) -> !s32i
-//      CIR-BEFORE: }
-
-//      CIR-AFTER: cir.func @_Z5test2b
-//      CIR-AFTER:   %[[#COND:]] = cir.load{{.*}} %{{.+}} : !cir.ptr<!cir.bool>, !cir.bool
-// CIR-AFTER-NEXT:   %[[#A:]] = cir.const #cir.int<1> : !s32i
-// CIR-AFTER-NEXT:   %[[#B:]] = cir.const #cir.int<2> : !s32i
-// CIR-AFTER-NEXT:   %{{.+}} = cir.select if %[[#COND]] then %[[#A]] else %[[#B]] : (!cir.bool, !s32i, !s32i) -> !s32i
-//      CIR-AFTER: }
-
-// LLVM: @_Z5test2b
-// LLVM:   %{{.+}} = select i1 %{{.+}}, i32 1, i32 2
-// LLVM: }