Added intersection of rewrite-based flags.

Author: rajatbajpai

llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp

@@ -3675,11 +3675,36 @@ static Value *foldSelectIntoAddConstant(SelectInst &SI,
       return nullptr;
 
     Value *NewSelect = Builder.CreateSelect(SI.getCondition(), X, Z, "", &SI);
-    cast<Instruction>(NewSelect)->setFastMathFlags(SI.getFastMathFlags());
     NewSelect->takeName(&SI);
 
-    Value *NewFAdd = Builder.CreateFAddFMF(NewSelect, C, FAdd);
+    Value *NewFAdd = Builder.CreateFAdd(NewSelect, C);
     NewFAdd->takeName(FAdd);
+
+    // Propagate rewrite-based flags
+    auto SelectFMF = SI.getFastMathFlags();
+    auto FAddFMF = FAdd->getFastMathFlags();
+    FastMathFlags CommonFMF, NewFAddFMF, NewSelectFMF;
+
+    CommonFMF.setAllowReassoc(SelectFMF.allowReassoc() &&
+                              FAddFMF.allowReassoc());
+    CommonFMF.setAllowReciprocal(SelectFMF.allowReciprocal() &&
+                                 FAddFMF.allowReciprocal());
+    CommonFMF.setAllowContract(SelectFMF.allowContract() &&
+                               FAddFMF.allowContract());
+    CommonFMF.setApproxFunc(SelectFMF.approxFunc() && FAddFMF.approxFunc());
+    NewSelectFMF = NewFAddFMF = CommonFMF;
+
+    // Propagate FastMath flags
+    NewFAddFMF.setNoNaNs(FAddFMF.noNaNs());
+    NewFAddFMF.setNoInfs(FAddFMF.noInfs());
+    NewFAddFMF.setNoSignedZeros(FAddFMF.noSignedZeros());
+    cast<Instruction>(NewFAdd)->setFastMathFlags(NewFAddFMF);
+
+    NewSelectFMF.setNoNaNs(SelectFMF.noNaNs());
+    NewSelectFMF.setNoInfs(SelectFMF.noInfs());
+    NewSelectFMF.setNoSignedZeros(SelectFMF.noSignedZeros());
+    cast<Instruction>(NewSelect)->setFastMathFlags(NewSelectFMF);
+
     return NewFAdd;
   }
 

llvm/test/Transforms/InstCombine/fcmp-fadd-select.ll

@@ -632,3 +632,30 @@ define float @test_fcmp_multiple_uses(float %in) {
   %res = fadd float %sel.1, %sel.2
   ret float %res
 }
+
+; Rewrite-based flags propagation
+define float @test_fcmp_ogt_fadd_select_rewrite_flags(float %in) {
+; CHECK-LABEL: define float @test_fcmp_ogt_fadd_select_rewrite_flags(
+; CHECK-SAME: float [[IN:%.*]]) {
+; CHECK-NEXT:    [[SEL_NEW:%.*]] = call reassoc nnan nsz arcp contract afn float @llvm.maxnum.f32(float [[IN]], float 0.000000e+00)
+; CHECK-NEXT:    [[ADD_NEW:%.*]] = fadd reassoc arcp contract afn float [[SEL_NEW]], 1.000000e+00
+; CHECK-NEXT:    ret float [[ADD_NEW]]
+;
+  %cmp1 = fcmp ogt float %in, 0.000000e+00
+  %add = fadd reassoc afn arcp contract float %in, 1.000000e+00
+  %sel = select nnan nsz reassoc afn arcp contract i1 %cmp1, float %add, float 1.000000e+00
+  ret float %sel
+}
+
+define float @test_fcmp_ogt_fadd_select_rewrite_and_fastmath(float %in) {
+; CHECK-LABEL: define float @test_fcmp_ogt_fadd_select_rewrite_and_fastmath(
+; CHECK-SAME: float [[IN:%.*]]) {
+; CHECK-NEXT:    [[SEL_NEW:%.*]] = call fast float @llvm.maxnum.f32(float [[IN]], float 0.000000e+00)
+; CHECK-NEXT:    [[ADD_NEW:%.*]] = fadd fast float [[SEL_NEW]], 1.000000e+00
+; CHECK-NEXT:    ret float [[ADD_NEW]]
+;
+  %cmp1 = fcmp ogt float %in, 0.000000e+00
+  %add = fadd fast float %in, 1.000000e+00
+  %sel = select fast i1 %cmp1, float %add, float 1.000000e+00
+  ret float %sel
+}