[ValueTracking] AllowEphemerals for alignment assumptions.

Allow AllowEphemerals in isValidAssumeForContext, as the CxtI might
be the producer of the pointer in the bundle. At the moment, align
assumptions aren't optimized away.

This allows using the assumption in the computeKnownBits call in
getConstantMultipleImpl.

We could extend the computeKnownBits API to allow callers to specify if
ephemerals are allowed, if the info from computeKnownBitsFromContext is
used to remove alignment assumptions.

Author: fhahn

llvm/lib/Analysis/ValueTracking.cpp

@@ -820,9 +820,12 @@ void llvm::computeKnownBitsFromContext(const Value *V, KnownBits &Known,
         continue;
       if (RetainedKnowledge RK = getKnowledgeFromBundle(
               *I, I->bundle_op_info_begin()[Elem.Index])) {
+        // Allow AllowEphemerals in isValidAssumeForContext, as the CxtI might
+        // be the producer of the pointer in the bundle. At the moment, align
+        // assumptions aren't optimized away.
         if (RK.WasOn == V && RK.AttrKind == Attribute::Alignment &&
             isPowerOf2_64(RK.ArgValue) &&
-            isValidAssumeForContext(I, Q.CxtI, Q.DT))
+            isValidAssumeForContext(I, Q.CxtI, Q.DT, /*AllowEphemerals*/ true))
           Known.Zero.setLowBits(Log2_64(RK.ArgValue));
       }
       continue;

llvm/test/Analysis/ScalarEvolution/max-backedge-taken-count-guard-info.ll

@@ -1777,23 +1777,23 @@ define void @ptr_induction_early_exit_eq_1_align_assumption_1(ptr %a, ptr %b, pt
 ; CHECK-LABEL: 'ptr_induction_early_exit_eq_1_align_assumption_1'
 ; CHECK-NEXT:  Classifying expressions for: @ptr_induction_early_exit_eq_1_align_assumption_1
 ; CHECK-NEXT:    %a_ = load ptr, ptr %a, align 8
-; CHECK-NEXT:    --> %a_ U: full-set S: full-set
+; CHECK-NEXT:    --> %a_ U: [0,-7) S: [-9223372036854775808,9223372036854775801)
 ; CHECK-NEXT:    %b_ = load ptr, ptr %b, align 8
-; CHECK-NEXT:    --> %b_ U: full-set S: full-set
+; CHECK-NEXT:    --> %b_ U: [0,-7) S: [-9223372036854775808,9223372036854775801)
 ; CHECK-NEXT:    %ptr.iv = phi ptr [ %ptr.iv.next, %loop.inc ], [ %a_, %entry ]
-; CHECK-NEXT:    --> {%a_,+,8}<nuw><%loop> U: full-set S: full-set Exits: <<Unknown>> LoopDispositions: { %loop: Computable }
+; CHECK-NEXT:    --> {%a_,+,8}<nuw><%loop> U: [0,-7) S: [-9223372036854775808,9223372036854775801) Exits: <<Unknown>> LoopDispositions: { %loop: Computable }
 ; CHECK-NEXT:    %ld1 = load ptr, ptr %ptr.iv, align 8
 ; CHECK-NEXT:    --> %ld1 U: full-set S: full-set Exits: <<Unknown>> LoopDispositions: { %loop: Variant }
 ; CHECK-NEXT:    %ptr.iv.next = getelementptr inbounds i8, ptr %ptr.iv, i64 8
-; CHECK-NEXT:    --> {(8 + %a_),+,8}<nw><%loop> U: full-set S: full-set Exits: <<Unknown>> LoopDispositions: { %loop: Computable }
+; CHECK-NEXT:    --> {(8 + %a_),+,8}<nw><%loop> U: [0,-7) S: [-9223372036854775808,9223372036854775801) Exits: <<Unknown>> LoopDispositions: { %loop: Computable }
 ; CHECK-NEXT:  Determining loop execution counts for: @ptr_induction_early_exit_eq_1_align_assumption_1
 ; CHECK-NEXT:  Loop %loop: <multiple exits> Unpredictable backedge-taken count.
 ; CHECK-NEXT:    exit count for loop: ***COULDNOTCOMPUTE***
-; CHECK-NEXT:    exit count for loop.inc: ***COULDNOTCOMPUTE***
-; CHECK-NEXT:  Loop %loop: Unpredictable constant max backedge-taken count.
-; CHECK-NEXT:  Loop %loop: Unpredictable symbolic max backedge-taken count.
+; CHECK-NEXT:    exit count for loop.inc: ((-8 + (-1 * (ptrtoint ptr %a_ to i64)) + (ptrtoint ptr %b_ to i64)) /u 8)
+; CHECK-NEXT:  Loop %loop: constant max backedge-taken count is i64 2305843009213693951
+; CHECK-NEXT:  Loop %loop: symbolic max backedge-taken count is ((-8 + (-1 * (ptrtoint ptr %a_ to i64)) + (ptrtoint ptr %b_ to i64)) /u 8)
 ; CHECK-NEXT:    symbolic max exit count for loop: ***COULDNOTCOMPUTE***
-; CHECK-NEXT:    symbolic max exit count for loop.inc: ***COULDNOTCOMPUTE***
+; CHECK-NEXT:    symbolic max exit count for loop.inc: ((-8 + (-1 * (ptrtoint ptr %a_ to i64)) + (ptrtoint ptr %b_ to i64)) /u 8)
 ;
 entry:
   %a_ = load ptr, ptr %a
@@ -1822,23 +1822,23 @@ define void @ptr_induction_early_exit_eq_1_align_assumption_2(ptr %a, ptr %b, pt
 ; CHECK-LABEL: 'ptr_induction_early_exit_eq_1_align_assumption_2'
 ; CHECK-NEXT:  Classifying expressions for: @ptr_induction_early_exit_eq_1_align_assumption_2
 ; CHECK-NEXT:    %a_ = load ptr, ptr %a, align 8
-; CHECK-NEXT:    --> %a_ U: full-set S: full-set
+; CHECK-NEXT:    --> %a_ U: [0,-7) S: [-9223372036854775808,9223372036854775801)
 ; CHECK-NEXT:    %b_ = load ptr, ptr %b, align 8
-; CHECK-NEXT:    --> %b_ U: full-set S: full-set
+; CHECK-NEXT:    --> %b_ U: [0,-7) S: [-9223372036854775808,9223372036854775801)
 ; CHECK-NEXT:    %ptr.iv = phi ptr [ %ptr.iv.next, %loop.inc ], [ %a_, %entry ]
-; CHECK-NEXT:    --> {%a_,+,8}<nuw><%loop> U: full-set S: full-set Exits: <<Unknown>> LoopDispositions: { %loop: Computable }
+; CHECK-NEXT:    --> {%a_,+,8}<nuw><%loop> U: [0,-7) S: [-9223372036854775808,9223372036854775801) Exits: <<Unknown>> LoopDispositions: { %loop: Computable }
 ; CHECK-NEXT:    %ld1 = load ptr, ptr %ptr.iv, align 8
 ; CHECK-NEXT:    --> %ld1 U: full-set S: full-set Exits: <<Unknown>> LoopDispositions: { %loop: Variant }
 ; CHECK-NEXT:    %ptr.iv.next = getelementptr inbounds i8, ptr %ptr.iv, i64 8
-; CHECK-NEXT:    --> {(8 + %a_),+,8}<nw><%loop> U: full-set S: full-set Exits: <<Unknown>> LoopDispositions: { %loop: Computable }
+; CHECK-NEXT:    --> {(8 + %a_),+,8}<nw><%loop> U: [0,-7) S: [-9223372036854775808,9223372036854775801) Exits: <<Unknown>> LoopDispositions: { %loop: Computable }
 ; CHECK-NEXT:  Determining loop execution counts for: @ptr_induction_early_exit_eq_1_align_assumption_2
 ; CHECK-NEXT:  Loop %loop: <multiple exits> Unpredictable backedge-taken count.
 ; CHECK-NEXT:    exit count for loop: ***COULDNOTCOMPUTE***
-; CHECK-NEXT:    exit count for loop.inc: ***COULDNOTCOMPUTE***
-; CHECK-NEXT:  Loop %loop: Unpredictable constant max backedge-taken count.
-; CHECK-NEXT:  Loop %loop: Unpredictable symbolic max backedge-taken count.
+; CHECK-NEXT:    exit count for loop.inc: ((-8 + (-1 * (ptrtoint ptr %a_ to i64)) + (ptrtoint ptr %b_ to i64)) /u 8)
+; CHECK-NEXT:  Loop %loop: constant max backedge-taken count is i64 2305843009213693951
+; CHECK-NEXT:  Loop %loop: symbolic max backedge-taken count is ((-8 + (-1 * (ptrtoint ptr %a_ to i64)) + (ptrtoint ptr %b_ to i64)) /u 8)
 ; CHECK-NEXT:    symbolic max exit count for loop: ***COULDNOTCOMPUTE***
-; CHECK-NEXT:    symbolic max exit count for loop.inc: ***COULDNOTCOMPUTE***
+; CHECK-NEXT:    symbolic max exit count for loop.inc: ((-8 + (-1 * (ptrtoint ptr %a_ to i64)) + (ptrtoint ptr %b_ to i64)) /u 8)
 ;
 entry:
   %a_ = load ptr, ptr %a