[CVP] Try to fold sdiv to constant

If we know that the sdiv result is a single constant, directly
use that instead of performing narrowing.

Fixes llvm#71659.

Author: nikic

llvm/lib/Transforms/Scalar/CorrelatedValuePropagation.cpp

@@ -910,6 +910,13 @@ static bool processSDiv(BinaryOperator *SDI, const ConstantRange &LCR,
   assert(SDI->getOpcode() == Instruction::SDiv);
   assert(!SDI->getType()->isVectorTy());
 
+  // Check whether the division folds to a constant.
+  if (const APInt *Elem = LCR.sdiv(RCR).getSingleElement()) {
+    SDI->replaceAllUsesWith(ConstantInt::get(SDI->getType(), *Elem));
+    SDI->eraseFromParent();
+    return true;
+  }
+
   struct Operand {
     Value *V;
     Domain D;

llvm/test/Transforms/CorrelatedValuePropagation/sdiv.ll

@@ -638,10 +638,7 @@ define void @sdiv_zero(ptr %p, i32 %arg) {
 ; CHECK-NEXT:    [[ADD:%.*]] = add i32 [[ARG:%.*]], 5
 ; CHECK-NEXT:    [[CMP:%.*]] = icmp ult i32 [[ADD]], 11
 ; CHECK-NEXT:    call void @llvm.assume(i1 [[CMP]])
-; CHECK-NEXT:    [[DIV_LHS_TRUNC:%.*]] = trunc i32 [[ARG]] to i8
-; CHECK-NEXT:    [[DIV1:%.*]] = sdiv i8 [[DIV_LHS_TRUNC]], 6
-; CHECK-NEXT:    [[DIV_SEXT:%.*]] = sext i8 [[DIV1]] to i32
-; CHECK-NEXT:    store i32 [[DIV_SEXT]], ptr [[P:%.*]], align 4
+; CHECK-NEXT:    store i32 0, ptr [[P:%.*]], align 4
 ; CHECK-NEXT:    ret void
 ;
   %add = add i32 %arg, 5
@@ -676,10 +673,7 @@ define void @sdiv_pos(ptr %p, i32 %arg) {
 ; CHECK-NEXT:    [[ADD:%.*]] = add i32 [[ARG:%.*]], -12
 ; CHECK-NEXT:    [[CMP:%.*]] = icmp ult i32 [[ADD]], 6
 ; CHECK-NEXT:    call void @llvm.assume(i1 [[CMP]])
-; CHECK-NEXT:    [[DIV1_LHS_TRUNC:%.*]] = trunc i32 [[ARG]] to i8
-; CHECK-NEXT:    [[DIV12:%.*]] = udiv i8 [[DIV1_LHS_TRUNC]], 6
-; CHECK-NEXT:    [[DIV1_ZEXT:%.*]] = zext i8 [[DIV12]] to i32
-; CHECK-NEXT:    store i32 [[DIV1_ZEXT]], ptr [[P:%.*]], align 4
+; CHECK-NEXT:    store i32 2, ptr [[P:%.*]], align 4
 ; CHECK-NEXT:    ret void
 ;
   %add = add i32 %arg, -12
@@ -695,12 +689,7 @@ define void @sdiv_neg(ptr %p, i32 %arg) {
 ; CHECK-NEXT:    [[ADD:%.*]] = add i32 [[ARG:%.*]], 17
 ; CHECK-NEXT:    [[CMP:%.*]] = icmp ult i32 [[ADD]], 6
 ; CHECK-NEXT:    call void @llvm.assume(i1 [[CMP]])
-; CHECK-NEXT:    [[ARG_NONNEG:%.*]] = sub i32 0, [[ARG]]
-; CHECK-NEXT:    [[DIV1_LHS_TRUNC:%.*]] = trunc i32 [[ARG_NONNEG]] to i8
-; CHECK-NEXT:    [[DIV12:%.*]] = udiv i8 [[DIV1_LHS_TRUNC]], 6
-; CHECK-NEXT:    [[DIV1_ZEXT:%.*]] = zext i8 [[DIV12]] to i32
-; CHECK-NEXT:    [[DIV1_NEG:%.*]] = sub i32 0, [[DIV1_ZEXT]]
-; CHECK-NEXT:    store i32 [[DIV1_NEG]], ptr [[P:%.*]], align 4
+; CHECK-NEXT:    store i32 -2, ptr [[P:%.*]], align 4
 ; CHECK-NEXT:    ret void
 ;
   %add = add i32 %arg, 17