[ValueTracking] Try to infer range of select from true and false values. (#68256)

When computing range of `select` instruction, first compute the union of
ranges of "True" and "False" operands of the `select` instruction.

Author: mgudim

llvm/lib/Analysis/ValueTracking.cpp

@@ -8841,9 +8841,14 @@ ConstantRange llvm::computeConstantRange(const Value *V, bool ForSigned,
     CR = ConstantRange::getNonEmpty(Lower, Upper);
   } else if (auto *II = dyn_cast<IntrinsicInst>(V))
     CR = getRangeForIntrinsic(*II);
-  else if (auto *SI = dyn_cast<SelectInst>(V))
-    CR = getRangeForSelectPattern(*SI, IIQ);
-  else if (isa<FPToUIInst>(V) || isa<FPToSIInst>(V)) {
+  else if (auto *SI = dyn_cast<SelectInst>(V)) {
+    ConstantRange CRTrue = computeConstantRange(
+        SI->getTrueValue(), ForSigned, UseInstrInfo, AC, CtxI, DT, Depth + 1);
+    ConstantRange CRFalse = computeConstantRange(
+        SI->getFalseValue(), ForSigned, UseInstrInfo, AC, CtxI, DT, Depth + 1);
+    CR = CRTrue.unionWith(CRFalse);
+    CR = CR.intersectWith(getRangeForSelectPattern(*SI, IIQ));
+  } else if (isa<FPToUIInst>(V) || isa<FPToSIInst>(V)) {
     APInt Lower = APInt(BitWidth, 0);
     APInt Upper = APInt(BitWidth, 0);
     // TODO: Return ConstantRange.

llvm/test/Analysis/BasicAA/range.ll

@@ -2,6 +2,7 @@
 
 %struct.S = type { i32, [2 x i32], i32 }
 %struct.S2 = type { i32, [4 x i32], [4 x i32] }
+@G = global [10 x i32] zeroinitializer, align 4
 
 ; CHECK: Function: t1
 ; CHECK: NoAlias: i32* %gep1, i32* %gep2
@@ -258,8 +259,19 @@ join:
   ret void
 }
 
-declare void @llvm.assume(i1)
 
+; CHECK-LABEL: Function: select_in_gep
+; CHECK: NoAlias: i32* %arrayidx, i32* getelementptr inbounds ([10 x i32], ptr @G, i64 0, i64 3)
+define i32 @select_in_gep(i1 %c)  {
+entry:
+  %select_ = select i1 %c, i64 2, i64 1
+  %arrayidx = getelementptr inbounds [10 x i32], ptr @G, i64 0, i64 %select_
+  store i32 42, ptr %arrayidx, align 4
+  %load_ = load i32, ptr getelementptr inbounds ([10 x i32], ptr @G, i64 0, i64 3), align 4
+  ret i32 %load_
+}
+
+declare void @llvm.assume(i1)
 
 !0 = !{ i32 0, i32 2 }
 !1 = !{ i32 0, i32 1 }

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

@@ -324,12 +324,12 @@ define i32 @sub_sel_op1_use(i1 %b) {
 ; CHECK-LABEL: @sub_sel_op1_use(
 ; CHECK-NEXT:    [[S:%.*]] = select i1 [[B:%.*]], i32 42, i32 41
 ; CHECK-NEXT:    call void @use(i32 [[S]])
-; CHECK-NEXT:    [[R:%.*]] = sub nsw i32 42, [[S]]
+; CHECK-NEXT:    [[R:%.*]] = sub nuw nsw i32 42, [[S]]
 ; CHECK-NEXT:    ret i32 [[R]]
 ;
   %s = select i1 %b, i32 42, i32 41
   call void @use(i32 %s)
-  %r = sub nsw i32 42, %s
+  %r = sub nuw nsw i32 42, %s
   ret i32 %r
 }