[ValueTracking] Handle trunc to i1 as condition in dominating condition. (llvm#126414)

proof: https://alive2.llvm.org/ce/z/gALGmv

Author: andjo403

llvm/lib/Analysis/ValueTracking.cpp

@@ -797,10 +797,28 @@ static void computeKnownBitsFromCond(const Value *V, Value *Cond,
     else
       Known2 = Known2.intersectWith(Known3);
     Known = Known.unionWith(Known2);
+    return;
   }
 
-  if (auto *Cmp = dyn_cast<ICmpInst>(Cond))
+  if (auto *Cmp = dyn_cast<ICmpInst>(Cond)) {
     computeKnownBitsFromICmpCond(V, Cmp, Known, SQ, Invert);
+    return;
+  }
+
+  if (match(Cond, m_Trunc(m_Specific(V)))) {
+    KnownBits DstKnown(1);
+    if (Invert) {
+      DstKnown.setAllZero();
+    } else {
+      DstKnown.setAllOnes();
+    }
+    if (cast<TruncInst>(Cond)->hasNoUnsignedWrap()) {
+      Known = Known.unionWith(DstKnown.zext(Known.getBitWidth()));
+      return;
+    }
+    Known = Known.unionWith(DstKnown.anyext(Known.getBitWidth()));
+    return;
+  }
 
   if (Depth < MaxAnalysisRecursionDepth && match(Cond, m_Not(m_Value(A))))
     computeKnownBitsFromCond(V, A, Known, Depth + 1, SQ, !Invert);
@@ -10280,6 +10298,10 @@ void llvm::findValuesAffectedByCondition(
                                                            m_Value()))) {
       // Handle patterns that computeKnownFPClass() support.
       AddAffected(A);
+    } else if (!IsAssume && match(V, m_Trunc(m_Value(X)))) {
+      // Assume is checked here as X is already added above for assumes in
+      // addValueAffectedByCondition
+      AddAffected(X);
     } else if (!IsAssume && match(V, m_Not(m_Value(X)))) {
       // Assume is checked here to avoid issues with ephemeral values
       Worklist.push_back(X);

llvm/test/Transforms/InstCombine/known-bits.ll

@@ -2167,11 +2167,9 @@ define i8 @test_trunc_and_1(i8 %a) {
 ; CHECK-NEXT:    [[CAST:%.*]] = trunc i8 [[A:%.*]] to i1
 ; CHECK-NEXT:    br i1 [[CAST]], label [[IF_THEN:%.*]], label [[IF_ELSE:%.*]]
 ; CHECK:       if.then:
-; CHECK-NEXT:    [[B:%.*]] = and i8 [[A]], 1
-; CHECK-NEXT:    ret i8 [[B]]
+; CHECK-NEXT:    ret i8 1
 ; CHECK:       if.else:
-; CHECK-NEXT:    [[C:%.*]] = and i8 [[A]], 1
-; CHECK-NEXT:    ret i8 [[C]]
+; CHECK-NEXT:    ret i8 0
 ;
 entry:
   %cast = trunc i8 %a to i1
@@ -2192,11 +2190,9 @@ define i8 @test_not_trunc_and_1(i8 %a) {
 ; CHECK-NEXT:    [[CAST:%.*]] = trunc i8 [[A:%.*]] to i1
 ; CHECK-NEXT:    br i1 [[CAST]], label [[IF_ELSE:%.*]], label [[IF_THEN:%.*]]
 ; CHECK:       if.then:
-; CHECK-NEXT:    [[B:%.*]] = and i8 [[A]], 1
-; CHECK-NEXT:    ret i8 [[B]]
+; CHECK-NEXT:    ret i8 0
 ; CHECK:       if.else:
-; CHECK-NEXT:    [[C:%.*]] = and i8 [[A]], 1
-; CHECK-NEXT:    ret i8 [[C]]
+; CHECK-NEXT:    ret i8 1
 ;
 entry:
   %cast = trunc i8 %a to i1
@@ -2243,11 +2239,9 @@ define i8 @test_trunc_nuw_and_1(i8 %a) {
 ; CHECK-NEXT:    [[CAST:%.*]] = trunc nuw i8 [[A:%.*]] to i1
 ; CHECK-NEXT:    br i1 [[CAST]], label [[IF_ELSE:%.*]], label [[IF_THEN:%.*]]
 ; CHECK:       if.then:
-; CHECK-NEXT:    [[B:%.*]] = and i8 [[A]], 1
-; CHECK-NEXT:    ret i8 [[B]]
+; CHECK-NEXT:    ret i8 0
 ; CHECK:       if.else:
-; CHECK-NEXT:    [[C:%.*]] = and i8 [[A]], 1
-; CHECK-NEXT:    ret i8 [[C]]
+; CHECK-NEXT:    ret i8 1
 ;
 entry:
   %cast = trunc nuw i8 %a to i1
@@ -2268,11 +2262,9 @@ define i8 @test_trunc_nuw_or_2(i8 %a) {
 ; CHECK-NEXT:    [[CAST:%.*]] = trunc nuw i8 [[A:%.*]] to i1
 ; CHECK-NEXT:    br i1 [[CAST]], label [[IF_ELSE:%.*]], label [[IF_THEN:%.*]]
 ; CHECK:       if.then:
-; CHECK-NEXT:    [[B:%.*]] = or i8 [[A]], 2
-; CHECK-NEXT:    ret i8 [[B]]
+; CHECK-NEXT:    ret i8 2
 ; CHECK:       if.else:
-; CHECK-NEXT:    [[C:%.*]] = or i8 [[A]], 2
-; CHECK-NEXT:    ret i8 [[C]]
+; CHECK-NEXT:    ret i8 3
 ;
 entry:
   %cast = trunc nuw i8 %a to i1
@@ -2293,11 +2285,9 @@ define i8 @test_not_trunc_nuw_and_1(i8 %a) {
 ; CHECK-NEXT:    [[CAST:%.*]] = trunc nuw i8 [[A:%.*]] to i1
 ; CHECK-NEXT:    br i1 [[CAST]], label [[IF_ELSE:%.*]], label [[IF_THEN:%.*]]
 ; CHECK:       if.then:
-; CHECK-NEXT:    [[B:%.*]] = and i8 [[A]], 1
-; CHECK-NEXT:    ret i8 [[B]]
+; CHECK-NEXT:    ret i8 0
 ; CHECK:       if.else:
-; CHECK-NEXT:    [[C:%.*]] = and i8 [[A]], 1
-; CHECK-NEXT:    ret i8 [[C]]
+; CHECK-NEXT:    ret i8 1
 ;
 entry:
   %cast = trunc nuw i8 %a to i1
@@ -2319,8 +2309,7 @@ define i8 @test_trunc_cond_and(i8 %x, i1 %c) {
 ; CHECK-NEXT:    [[COND:%.*]] = and i1 [[C:%.*]], [[CMP]]
 ; CHECK-NEXT:    br i1 [[COND]], label [[IF:%.*]], label [[EXIT:%.*]]
 ; CHECK:       if:
-; CHECK-NEXT:    [[OR1:%.*]] = or i8 [[X]], -2
-; CHECK-NEXT:    ret i8 [[OR1]]
+; CHECK-NEXT:    ret i8 -1
 ; CHECK:       exit:
 ; CHECK-NEXT:    [[OR2:%.*]] = or i8 [[X]], -2
 ; CHECK-NEXT:    ret i8 [[OR2]]
@@ -2345,8 +2334,7 @@ define i8 @test_not_trunc_cond_and(i8 %x, i1 %c) {
 ; CHECK-NEXT:    [[COND:%.*]] = and i1 [[C:%.*]], [[NOT]]
 ; CHECK-NEXT:    br i1 [[COND]], label [[IF:%.*]], label [[EXIT:%.*]]
 ; CHECK:       if:
-; CHECK-NEXT:    [[OR1:%.*]] = or i8 [[X]], -2
-; CHECK-NEXT:    ret i8 [[OR1]]
+; CHECK-NEXT:    ret i8 -2
 ; CHECK:       exit:
 ; CHECK-NEXT:    [[OR2:%.*]] = or i8 [[X]], -2
 ; CHECK-NEXT:    ret i8 [[OR2]]