Index: llvm/lib/Support/KnownBits.cpp
===================================================================
--- llvm/lib/Support/KnownBits.cpp
+++ llvm/lib/Support/KnownBits.cpp
@@ -421,11 +421,25 @@
          "Self multiplication knownbits mismatch");
 
   // Compute a conservative estimate for high known-0 bits.
+  // TODO: This could be generalized to number of sign bits (negative numbers).
   unsigned LHSLeadZ = LHS.countMinLeadingZeros();
   unsigned RHSLeadZ = RHS.countMinLeadingZeros();
   unsigned LeadZ = std::max(LHSLeadZ + RHSLeadZ, BitWidth) - BitWidth;
   assert(LeadZ <= BitWidth && "More zeros than bits?");
 
+  if (LeadZ) {
+    // Special-case: if one of the operands is 0/1, then the result has at least
+    // as many leading zeros as the other op (X*0 = 0, X*1 = X). This is always
+    // an improvement of the above estimate.
+    if (LHSLeadZ == BitWidth - 1) {
+      assert(LeadZ < RHSLeadZ && "Specialization should only improve estimate");
+      LeadZ = RHSLeadZ;
+    } else if (RHSLeadZ == BitWidth - 1) {
+      assert(LeadZ < LHSLeadZ && "Specialization should only improve estimate");
+      LeadZ = LHSLeadZ;
+    }
+  }
+
   // The result of the bottom bits of an integer multiply can be
   // inferred by looking at the bottom bits of both operands and
   // multiplying them together.
Index: llvm/test/Transforms/InstCombine/icmp-mul.ll
===================================================================
--- llvm/test/Transforms/InstCombine/icmp-mul.ll
+++ llvm/test/Transforms/InstCombine/icmp-mul.ll
@@ -684,11 +684,7 @@
 
 define i1 @mul_of_bool(i32 %x, i8 %y) {
 ; CHECK-LABEL: @mul_of_bool(
-; CHECK-NEXT:    [[B:%.*]] = and i32 [[X:%.*]], 1
-; CHECK-NEXT:    [[Z:%.*]] = zext i8 [[Y:%.*]] to i32
-; CHECK-NEXT:    [[M:%.*]] = mul nuw nsw i32 [[B]], [[Z]]
-; CHECK-NEXT:    [[R:%.*]] = icmp ugt i32 [[M]], 255
-; CHECK-NEXT:    ret i1 [[R]]
+; CHECK-NEXT:    ret i1 false
 ;
   %b = and i32 %x, 1
   %z = zext i8 %y to i32
@@ -699,11 +695,7 @@
 
 define i1 @mul_of_bool_commute(i32 %x, i32 %y) {
 ; CHECK-LABEL: @mul_of_bool_commute(
-; CHECK-NEXT:    [[X1:%.*]] = and i32 [[X:%.*]], 1
-; CHECK-NEXT:    [[Y8:%.*]] = and i32 [[Y:%.*]], 255
-; CHECK-NEXT:    [[M:%.*]] = mul nuw nsw i32 [[Y8]], [[X1]]
-; CHECK-NEXT:    [[R:%.*]] = icmp ugt i32 [[M]], 255
-; CHECK-NEXT:    ret i1 [[R]]
+; CHECK-NEXT:    ret i1 false
 ;
   %x1 = and i32 %x, 1
   %y8 = and i32 %y, 255
@@ -714,11 +706,7 @@
 
 define i1 @mul_of_bools(i32 %x, i32 %y) {
 ; CHECK-LABEL: @mul_of_bools(
-; CHECK-NEXT:    [[X1:%.*]] = and i32 [[X:%.*]], 1
-; CHECK-NEXT:    [[Y1:%.*]] = and i32 [[Y:%.*]], 1
-; CHECK-NEXT:    [[M:%.*]] = mul nuw nsw i32 [[X1]], [[Y1]]
-; CHECK-NEXT:    [[R:%.*]] = icmp ult i32 [[M]], 2
-; CHECK-NEXT:    ret i1 [[R]]
+; CHECK-NEXT:    ret i1 true
 ;
   %x1 = and i32 %x, 1
   %y1 = and i32 %y, 1
@@ -727,6 +715,8 @@
   ret i1 %r
 }
 
+; negative test - not a mask of low bit
+
 define i1 @not_mul_of_bool(i32 %x, i8 %y) {
 ; CHECK-LABEL: @not_mul_of_bool(
 ; CHECK-NEXT:    [[Q:%.*]] = and i32 [[X:%.*]], 3
@@ -742,6 +732,8 @@
   ret i1 %r
 }
 
+; negative test - not a single low bit
+
 define i1 @not_mul_of_bool_commute(i32 %x, i32 %y) {
 ; CHECK-LABEL: @not_mul_of_bool_commute(
 ; CHECK-NEXT:    [[X30:%.*]] = lshr i32 [[X:%.*]], 30
@@ -757,6 +749,9 @@
   ret i1 %r
 }
 
+; negative test - no leading zeros for 's'
+; TODO: If analysis was generalized for sign bits, we could reduce this to false.
+
 define i1 @mul_of_bool_no_lz_other_op(i32 %x, i8 %y) {
 ; CHECK-LABEL: @mul_of_bool_no_lz_other_op(
 ; CHECK-NEXT:    [[B:%.*]] = and i32 [[X:%.*]], 1