[SLP]Fix PR61224: Compiler hits infinite loop.

IRBuilder in many cases is able to fold constant code automatically,
but in some cases (for some intrinsics) it cannot do it. Need to perform
manual calculation, if constant provided in these corner cases, to avoid
infinite loop.

Author: alexey-bataev

llvm/lib/Transforms/Vectorize/SLPVectorizer.cpp

@@ -12235,6 +12235,7 @@ class HorizontalReduction {
   static Value *createOp(IRBuilder<> &Builder, RecurKind Kind, Value *LHS,
                          Value *RHS, const Twine &Name, bool UseSelect) {
     unsigned RdxOpcode = RecurrenceDescriptor::getOpcode(Kind);
+    bool IsConstant = isConstant(LHS) && isConstant(RHS);
     switch (Kind) {
     case RecurKind::Or:
       if (UseSelect &&
@@ -12256,29 +12257,37 @@ class HorizontalReduction {
       return Builder.CreateBinOp((Instruction::BinaryOps)RdxOpcode, LHS, RHS,
                                  Name);
     case RecurKind::FMax:
+      if (IsConstant)
+        return ConstantFP::get(LHS->getType(),
+                               maxnum(cast<ConstantFP>(LHS)->getValueAPF(),
+                                      cast<ConstantFP>(RHS)->getValueAPF()));
       return Builder.CreateBinaryIntrinsic(Intrinsic::maxnum, LHS, RHS);
     case RecurKind::FMin:
+      if (IsConstant)
+        return ConstantFP::get(LHS->getType(),
+                               minnum(cast<ConstantFP>(LHS)->getValueAPF(),
+                                      cast<ConstantFP>(RHS)->getValueAPF()));
       return Builder.CreateBinaryIntrinsic(Intrinsic::minnum, LHS, RHS);
     case RecurKind::SMax:
-      if (UseSelect) {
+      if (IsConstant || UseSelect) {
         Value *Cmp = Builder.CreateICmpSGT(LHS, RHS, Name);
         return Builder.CreateSelect(Cmp, LHS, RHS, Name);
       }
       return Builder.CreateBinaryIntrinsic(Intrinsic::smax, LHS, RHS);
     case RecurKind::SMin:
-      if (UseSelect) {
+      if (IsConstant || UseSelect) {
         Value *Cmp = Builder.CreateICmpSLT(LHS, RHS, Name);
         return Builder.CreateSelect(Cmp, LHS, RHS, Name);
       }
       return Builder.CreateBinaryIntrinsic(Intrinsic::smin, LHS, RHS);
     case RecurKind::UMax:
-      if (UseSelect) {
+      if (IsConstant || UseSelect) {
         Value *Cmp = Builder.CreateICmpUGT(LHS, RHS, Name);
         return Builder.CreateSelect(Cmp, LHS, RHS, Name);
       }
       return Builder.CreateBinaryIntrinsic(Intrinsic::umax, LHS, RHS);
     case RecurKind::UMin:
-      if (UseSelect) {
+      if (IsConstant || UseSelect) {
         Value *Cmp = Builder.CreateICmpULT(LHS, RHS, Name);
         return Builder.CreateSelect(Cmp, LHS, RHS, Name);
       }

llvm/test/Transforms/SLPVectorizer/X86/reduce-constants.ll

@@ -0,0 +1,18 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
+; RUN: opt -S -mtriple=x86_64 -passes=slp-vectorizer < %s | FileCheck %s
+
+define double @test(double %m, double %a) {
+; CHECK-LABEL: @test(
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    [[TMP0:%.*]] = call fast double @llvm.maxnum.f64(double 0.000000e+00, double [[M:%.*]])
+; CHECK-NEXT:    [[TMP1:%.*]] = call fast double @llvm.maxnum.f64(double [[TMP0]], double [[A:%.*]])
+; CHECK-NEXT:    ret double [[TMP1]]
+;
+entry:
+  %c = tail call fast double @llvm.maxnum.f64(double %m, double 0.000000e+00)
+  %c1 = tail call fast double @llvm.maxnum.f64(double %a, double %c)
+  %c2 = tail call fast double @llvm.maxnum.f64(double %c1, double 0.000000e+00)
+  ret double %c2
+}
+
+declare double @llvm.maxnum.f64(double, double)