[InstCombine] propagate IR flags from binop through select

The tests with constant folding that produces poison
could potentially remove the select entirely:
https://alive2.llvm.org/ce/z/e-WUqF
...but this patch just removes the FMF-only limitation on
propagation.

Author: rotateright

llvm/lib/Transforms/InstCombine/InstructionCombining.cpp

@@ -1027,13 +1027,11 @@ static Value *foldOperationIntoSelectOperand(Instruction &I, Value *SO,
   if (!ConstIsRHS)
     std::swap(Op0, Op1);
 
-  auto *BO = cast<BinaryOperator>(&I);
-  Value *RI = Builder.CreateBinOp(BO->getOpcode(), Op0, Op1,
-                                  SO->getName() + ".op");
-  auto *FPInst = dyn_cast<Instruction>(RI);
-  if (FPInst && isa<FPMathOperator>(FPInst))
-    FPInst->copyFastMathFlags(BO);
-  return RI;
+  Value *NewBO = Builder.CreateBinOp(cast<BinaryOperator>(&I)->getOpcode(), Op0,
+                                     Op1, SO->getName() + ".op");
+  if (auto *NewBOI = dyn_cast<Instruction>(NewBO))
+    NewBOI->copyIRFlags(&I);
+  return NewBO;
 }
 
 Instruction *InstCombinerImpl::FoldOpIntoSelect(Instruction &Op,

llvm/test/Transforms/InstCombine/select-2.ll

@@ -45,7 +45,7 @@ define float @t3(float %x, float %y) {
 
 define i8 @ashr_exact_poison_constant_fold(i1 %b, i8 %x) {
 ; CHECK-LABEL: @ashr_exact_poison_constant_fold(
-; CHECK-NEXT:    [[X_OP:%.*]] = ashr i8 [[X:%.*]], 3
+; CHECK-NEXT:    [[X_OP:%.*]] = ashr exact i8 [[X:%.*]], 3
 ; CHECK-NEXT:    [[R:%.*]] = select i1 [[B:%.*]], i8 [[X_OP]], i8 5
 ; CHECK-NEXT:    ret i8 [[R]]
 ;
@@ -56,7 +56,7 @@ define i8 @ashr_exact_poison_constant_fold(i1 %b, i8 %x) {
 
 define i8 @ashr_exact(i1 %b, i8 %x) {
 ; CHECK-LABEL: @ashr_exact(
-; CHECK-NEXT:    [[X_OP:%.*]] = ashr i8 [[X:%.*]], 3
+; CHECK-NEXT:    [[X_OP:%.*]] = ashr exact i8 [[X:%.*]], 3
 ; CHECK-NEXT:    [[R:%.*]] = select i1 [[B:%.*]], i8 [[X_OP]], i8 2
 ; CHECK-NEXT:    ret i8 [[R]]
 ;
@@ -67,7 +67,7 @@ define i8 @ashr_exact(i1 %b, i8 %x) {
 
 define i8 @shl_nsw_nuw_poison_constant_fold(i1 %b, i8 %x) {
 ; CHECK-LABEL: @shl_nsw_nuw_poison_constant_fold(
-; CHECK-NEXT:    [[X_OP:%.*]] = shl i8 16, [[X:%.*]]
+; CHECK-NEXT:    [[X_OP:%.*]] = shl nuw nsw i8 16, [[X:%.*]]
 ; CHECK-NEXT:    [[R:%.*]] = select i1 [[B:%.*]], i8 -128, i8 [[X_OP]]
 ; CHECK-NEXT:    ret i8 [[R]]
 ;
@@ -78,7 +78,7 @@ define i8 @shl_nsw_nuw_poison_constant_fold(i1 %b, i8 %x) {
 
 define i8 @shl_nsw_nuw(i1 %b, i8 %x) {
 ; CHECK-LABEL: @shl_nsw_nuw(
-; CHECK-NEXT:    [[X_OP:%.*]] = shl i8 7, [[X:%.*]]
+; CHECK-NEXT:    [[X_OP:%.*]] = shl nuw nsw i8 7, [[X:%.*]]
 ; CHECK-NEXT:    [[R:%.*]] = select i1 [[B:%.*]], i8 56, i8 [[X_OP]]
 ; CHECK-NEXT:    ret i8 [[R]]
 ;
@@ -89,7 +89,7 @@ define i8 @shl_nsw_nuw(i1 %b, i8 %x) {
 
 define i8 @add_nsw_poison_constant_fold(i1 %b, i8 %x) {
 ; CHECK-LABEL: @add_nsw_poison_constant_fold(
-; CHECK-NEXT:    [[X_OP:%.*]] = add i8 [[X:%.*]], 64
+; CHECK-NEXT:    [[X_OP:%.*]] = add nsw i8 [[X:%.*]], 64
 ; CHECK-NEXT:    [[R:%.*]] = select i1 [[B:%.*]], i8 [[X_OP]], i8 -127
 ; CHECK-NEXT:    ret i8 [[R]]
 ;
@@ -100,7 +100,7 @@ define i8 @add_nsw_poison_constant_fold(i1 %b, i8 %x) {
 
 define i8 @add_nsw(i1 %b, i8 %x) {
 ; CHECK-LABEL: @add_nsw(
-; CHECK-NEXT:    [[X_OP:%.*]] = add i8 [[X:%.*]], 64
+; CHECK-NEXT:    [[X_OP:%.*]] = add nsw i8 [[X:%.*]], 64
 ; CHECK-NEXT:    [[R:%.*]] = select i1 [[B:%.*]], i8 [[X_OP]], i8 71
 ; CHECK-NEXT:    ret i8 [[R]]
 ;