[InstCombine] Generalize to handle non-rem-zero cases

Author: dtcxzyw

llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp

@@ -2239,11 +2239,11 @@ static Instruction *foldICmpShlLHSC(ICmpInst &Cmp, Instruction *Shl,
   unsigned TypeBits = C.getBitWidth();
   ICmpInst::Predicate Pred = Cmp.getPredicate();
   if (Cmp.isUnsigned()) {
+    assert(!C2->isZero() && C2->ult(C) &&
+           "Should be simplified by InstSimplify");
     APInt Div, Rem;
     APInt::udivrem(C, *C2, Div, Rem);
-    if (!Rem.isZero())
-      return nullptr;
-    bool CIsPowerOf2 = Div.isPowerOf2();
+    bool CIsPowerOf2 = Rem.isZero() && Div.isPowerOf2();
 
     // (1 << Y) pred C -> Y pred Log2(C)
     if (!CIsPowerOf2) {

llvm/test/Transforms/InstCombine/icmp-shl-nuw.ll

@@ -138,8 +138,7 @@ define i1 @fold_icmp_shl_nuw_c2_div_non_pow2(i32 %x) {
 
 define i1 @fold_icmp_shl_nuw_c2_indivisible(i32 %x) {
 ; CHECK-LABEL: @fold_icmp_shl_nuw_c2_indivisible(
-; CHECK-NEXT:    [[SHL:%.*]] = shl nuw i32 16, [[X:%.*]]
-; CHECK-NEXT:    [[CMP:%.*]] = icmp ult i32 [[SHL]], 63
+; CHECK-NEXT:    [[CMP:%.*]] = icmp ult i32 [[X:%.*]], 2
 ; CHECK-NEXT:    ret i1 [[CMP]]
 ;
   %shl = shl nuw i32 16, %x
@@ -157,3 +156,23 @@ define i1 @fold_icmp_shl_c2_without_nuw(i32 %x) {
   %cmp = icmp ult i32 %shl, 64
   ret i1 %cmp
 }
+
+; Make sure this trivial case is folded by InstSimplify.
+define i1 @fold_icmp_shl_nuw_c2_precondition1(i32 %x) {
+; CHECK-LABEL: @fold_icmp_shl_nuw_c2_precondition1(
+; CHECK-NEXT:    ret i1 true
+;
+  %shl = shl nuw i32 0, %x
+  %cmp = icmp ult i32 %shl, 63
+  ret i1 %cmp
+}
+
+; Make sure this trivial case is folded by InstSimplify.
+define i1 @fold_icmp_shl_nuw_c2_precondition2(i32 %x) {
+; CHECK-LABEL: @fold_icmp_shl_nuw_c2_precondition2(
+; CHECK-NEXT:    ret i1 false
+;
+  %shl = shl nuw i32 127, %x
+  %cmp = icmp ult i32 %shl, 63
+  ret i1 %cmp
+}